Android Firebase => GridView MasterDetail - Save,Read,Show

android crud

This is an android firebase tutorial. The aim is to write, read and show data in a GridView.

User can then click a particular gridview item and move to a new activity transferring data over there.

Let's go.

Project Summary

No. File Major Responsibility
1. Spacecraft.java Represents a single Spacecraft and it's properties like name,propellant and description.
2. FirebaseHelper.java This class has allows us perform Firebase CRUD operations.
3. CustomAdapter.java Our adapter class
4. DetailActivity.java Our Detail Activity to show a single spacecraft's details.
5. MainActivity.java Our Master Activity. It shows the grid of Spacecrafts
6. activity_main.xml Our Master Activity's layout.
7. content_main.xml Our Master Activity's content detail.
8. activity_detail.xml Our Detail Activity's main layout.
9. content_detail.xml Our Detail Activity's content layout.
10. input_dialog.xml Our input dialog layout.
11. model.xml Each GridView's grid model.

1. Create Basic Activity Project

  1. First create an empty project in android studio. Go to File --> New Project.

  2. Type the application name and choose the company name. New Project Dialog

  3. Choose minimum SDK. Choose minimum SDK

  4. Choose Basic activity. Choose Empty Activity

  5. Click Finish. Finish

Basic activity will have a toolbar and floating action button already added in the layout

Normally two layouts get generated with this option:

No. Name Type Description
1. activity_main.xml XML Layout Will get inflated into MainActivity Layout.Typically contains appbarlayout with toolbar.Also has a floatingactionbutton.
2. content_main.xml XML Layout Will be included into activity_main.xml.You add your views and widgets here.
3. MainActivity.java Class Main Activity.

In this example I used a basic activity.

The activity will automatically be registered in the android_manifest.xml. Android Activities are components and normally need to be registered as an application component.

If you've created yours manually then register it inside the <application>...<application> as following, replacing the MainActivity with your activity name:


        <activity android:name=".MainActivity">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

You can see that one action and category are specified as intent filters. The category makes our MainActivity as launcher activity. Launcher activities get executed first when th android app is run.

Advantage of Creating Basic Activity project

You can optionally choose empty activity over basic activity for this project.

However basic activity has the following advantages:

No. Advantage
1. Provides us a readymade toolbar which gives us actionbar features yet easily customizable
2. Provides us with appbar layout which implements material design appbar concepts.
3. Provides a FloatinActionButton which we can readily use to initiate quick actions especially in examples like these.
4. Decouples our custom content views and widgets from the templating features like toolbar.

Generated Project Structure

AndroidStudio will generate for you a project with default configurations via a set of files and directories.

Here are the most important of them:

No. File Major Responsibility
1. build/ A directory containing resources that have been compiled from the building of application and the classes generated by android tools. Such a tool is the R.java file. R.java file normally holds the references to application resources.
2. libs/ To hold libraries we use in our project.
3. src/main/ To hold the source code of our application.This is the main folder you work with.
4. src/main/java/ Contains our java classes organized as packages.
5. src/main/res/ Contains our project resources folders as follows.
6. src/main/res/drawable/ Contains our drawable resources.
7. src/main/res/layout/ Contains our layout resources.
8. src/main/res/menu/ Contains our menu resources XML code.
9. src/main/res/values/ Contains our values resources XML code.These define sets of name-value pairs and can be strings, styles and colors.
10. AndroidManifest.xml This file gets autogenerated when we create an android project.It will define basic information needed by the android system like application name,package name,permissions,activities,intents etc.
11. build.gradle Gradle Script used to build the android app.

2. Add Firebase Configurations

Go ahead create you Firebase Database realtime in your Firebase account.

Then download the google.json file and add it to your project at the app level:

3. Add Dependencies

In your dependencies add Firebase dependencies then apply the googleservices plugin as below:

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.3.0'
    compile 'com.android.support:design:23.3.0'
    compile 'com.android.support:cardview-v7:23.3.0'

    compile 'com.google.firebase:firebase-core:9.0.2'
    compile 'com.google.firebase:firebase-database:9.0.2'
}
apply plugin: 'com.google.gms.google-services'

4. Create Second Activity

Go ahead create a SecondActivity that will be used as the Detail View.

It will display selected Spacecraft details.

We'll look at its source later. However note that it will add two XML layouts: activity_detail and content_detail to our layout resources.

5. Our Layouts

User interfaces are typically created in android using XML layouts as opposed by direct java coding.

This is an example fo declarative programming.

Advantages of Using XML over Java
No. Advantage
1. Declarative creation of widgets and views allows us to use a declarative language XML which makes is easier.
2. It's easily maintanable as the user interface is decoupled from your Java logic.
3. It's easier to share or download code and safely test them before runtime.
4. You can use XML generated tools to generate XML

Here are our layouts for this project:

(a). activity_main.xml
  • This layout gets inflated to MainActivity user interface.
  • It includes the content_main.xml.
  • MainActivity is our Master View.

Here are some of the widgets, views and viewgroups that get employed"

No. View/ViewGroup Package Role
1. CordinatorLayout android.support.design.widget Super-powered framelayout that provides our application's top level decoration and is also specifies interactions and behavioros of all it's children.
2. AppBarLayout android.support.design.widget A LinearLayout child that arranges its children vertically and provides material design app bar concepts like scrolling gestures.
3. ToolBar <android.support.v7.widget A ViewGroup that can provide actionbar features yet still be used within application layouts.
4. FloatingActionButton android.support.design.widget An circular imageview floating above the UI that we can use as buttons.
(b). content_main.xml

This layout gets included in your activity_main.xml. We define our GridView here.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.tutorials.hp.firebasegridviewmdetail.MainActivity"
    tools:showIn="@layout/activity_main">

    <GridView
        android:id="@+id/gv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:numColumns="2"
         />
</RelativeLayout>
(c). activity_detail.xml

Our SecondActivity's layout. Virtually the same as the activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.tutorials.hp.firebasegridviewmdetail.DetailActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_detail" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:src="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>
(d). content_detail.xml

The SecondActivity's content layout.

Will be included into the activity_detail.xml.

We add a CardView with an imageview and TextView that will be used to show the details of our Spacecraft.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.tutorials.hp.firebasegridviewmdetail.DetailActivity"
    tools:showIn="@layout/activity_detail">

    <android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="horizontal" android:layout_width="match_parent"
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:layout_margin="5dp"
        card_view:cardCornerRadius="10dp"
        card_view:cardElevation="5dp"

        android:layout_height="match_parent">

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:weightSum="1">

            <LinearLayout
                android:orientation="horizontal"
                android:layout_width="match_parent"
                android:layout_height="wrap_content">

                <ImageView
                    android:id="@+id/articleDetailImg"
                    android:layout_width="320dp"
                    android:layout_height="wrap_content"
                    android:paddingLeft="10dp"
                    android:layout_alignParentTop="true"
                    android:scaleType="centerCrop"
                    android:src="@drawable/spitzer" />

                <LinearLayout
                    android:orientation="vertical"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content">

                    <TextView
                        android:id="@+id/nameDetailTxt"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:textAppearance="?android:attr/textAppearanceLarge"
                        android:padding="5dp"
                        android:minLines="1"
                        android:textStyle="bold"
                        android:textColor="@color/colorAccent"
                        android:text="Title" />

                    <TextView
                        android:id="@+id/descDetailTxt"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:textAppearance="?android:attr/textAppearanceLarge"
                        android:padding="5dp"
                        android:textColor="#0f0f0f"
                        android:minLines="4"
                        android:text="Space craft details...." />

                </LinearLayout>
            </LinearLayout>

            <LinearLayout
                android:layout_width="fill_parent"
                android:layout_height="match_parent"
                android:layout_marginTop="?attr/actionBarSize"
                android:orientation="vertical"
                android:paddingLeft="5dp"
                android:paddingRight="5dp"
                android:paddingTop="5dp">

                <TextView
                    android:id="@+id/propellantDetailTxt"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textAppearance="?android:attr/textAppearanceLarge"
                    android:padding="5dp"
                    android:minLines="1"
                    android:text="DATE" />

                <TextView
                    android:id="@+id/linkDetailTxt"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textAppearance="?android:attr/textAppearanceMedium"
                    android:padding="5dp"
                    android:textColor="@color/colorPrimaryDark"
                    android:textStyle="italic"
                    android:text="Link" />
            </LinearLayout>
        </LinearLayout>
    </android.support.v7.widget.CardView>
</RelativeLayout>
(e). input_dialog.xml

This layout will be inflated into a dialog. Our input dialog.

Users can then perform CRUD via this layout.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="?attr/actionBarSize"
        android:orientation="vertical"
        android:paddingLeft="15dp"
        android:paddingRight="15dp"
        android:paddingTop="50dp">

        <android.support.design.widget.TextInputLayout
            android:id="@+id/nameLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <EditText
                android:id="@+id/nameEditText"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:singleLine="true"
                android:hint= "Name" />
        </android.support.design.widget.TextInputLayout>

        <android.support.design.widget.TextInputLayout
            android:id="@+id/propLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <EditText
                android:id="@+id/propellantEditText"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:singleLine="true"
                android:hint= "Propellant" />

        <android.support.design.widget.TextInputLayout
            android:id="@+id/descLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <EditText
                android:id="@+id/descEditText"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:singleLine="true"
                android:hint= "Description" />
        </android.support.design.widget.TextInputLayout>

       </android.support.design.widget.TextInputLayout>

        <Button android:id="@+id/saveBtn"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Save"
            android:clickable="true"
            android:background="@color/colorAccent"
            android:layout_marginTop="40dp"
           android:textColor="@android:color/white"/>
    </LinearLayout>
</LinearLayout>
(f). model.xml

Our GridView will have images and text from our Firebase. We therefore need to create a custom model layout for each Grid.

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_margin="10dp"
    card_view:cardCornerRadius="5dp"
    card_view:cardElevation="5dp"
    android:layout_height="200dp">

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceLarge"
                android:text="Name"
                android:id="@+id/nameTxt"
                android:padding="10dp"
                android:textColor="@color/colorAccent"
                android:textStyle="bold"
                android:layout_alignParentLeft="true"
                />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceLarge"
                android:text="Description....................."
                android:lines="3"
                android:id="@+id/descTxt"
                android:padding="10dp"
                android:layout_alignParentLeft="true"
                />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:text="Propellant"
                android:textStyle="italic"
                android:id="@+id/propellantTxt" />
    </LinearLayout>
</android.support.v7.widget.CardView>

6. Java Classes

Android projects get written in Java so let's write some Java code for our Firebase project.

(a). Spacecraft.java

This is our data object class. Here's its responsibilities:

No. Responsibility
1. Represents a Single Spacecraft
2. Set Spacecraft properties: name,propellant and description.
3. Get Spacecraft properties: name,propellant and description.
package com.tutorials.hp.firebasegridviewmdetail.m_Model;

/
 * 1. OUR MODEL CLASS
 */
public class Spacecraft {

    String name,propellant,description;

    public Spacecraft() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPropellant() {
        return propellant;
    }

    public void setPropellant(String propellant) {
        this.propellant = propellant;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}
(b). FirebaseHelper.java

This class allows us perform save and retrieve data to Firebase Realtime database.

No. Responsibility
1. Keep hold of three Objects: DatabaseReference,a Boolean saved value, and an ArrayList of Spacecrafts.
2. Obtain a DatabaseReference object via the constructor and Assign it to our local db data member.
3. Take a Spacecraft object and save it to Firebase this returning a Boolean indicating success or failure.
4. Loop through DataSnapshot children nodes obtaining all the Spacecraft objects from Firebase and fill our local arraylist with those objects.
5. Listen to Firebase Children mutation events like when a DataSnapshot child has been added, moved, removed, changed or cancelled. This allows us to fetch data in realtime.
package com.tutorials.hp.firebasegridviewmdetail.m_FireBase;

import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseException;
import com.google.firebase.database.DatabaseReference;
import com.tutorials.hp.firebasegridviewmdetail.m_Model.Spacecraft;

import java.util.ArrayList;

/
 * 1.SAVE DATA TO FIREBASE
 * 2. RETRIEVE
 * 3.RETURN AN ARRAYLIST
 */
public class FirebaseHelper {

    DatabaseReference db;
    Boolean saved=null;
    ArrayList<Spacecraft> spacecrafts=new ArrayList<>();

    public FirebaseHelper(DatabaseReference db) {
        this.db = db;
    }
    //WRITE IF NOT NULL
    public Boolean save(Spacecraft spacecraft)
    {
        if(spacecraft==null)
        {
            saved=false;
        }else
        {
            try
            {
                db.child("Spacecraft").push().setValue(spacecraft);
                saved=true;

            }catch (DatabaseException e)
            {
                e.printStackTrace();
                saved=false;
            }
        }

        return saved;
    }
    //IMPLEMENT FETCH DATA AND FILL ARRAYLIST
    private void fetchData(DataSnapshot dataSnapshot)
    {
        spacecrafts.clear();

        for (DataSnapshot ds : dataSnapshot.getChildren())
        {
            Spacecraft spacecraft=ds.getValue(Spacecraft.class);
            spacecrafts.add(spacecraft);
        }
    }
    //READ BY HOOKING ONTO DATABASE OPERATION CALLBACKS
    public ArrayList<Spacecraft> retrieve() {
       db.addChildEventListener(new ChildEventListener() {
           @Override
           public void onChildAdded(DataSnapshot dataSnapshot, String s) {
               fetchData(dataSnapshot);
           }
           @Override
           public void onChildChanged(DataSnapshot dataSnapshot, String s) {
               fetchData(dataSnapshot);

           }
           @Override
           public void onChildRemoved(DataSnapshot dataSnapshot) {

           }

           @Override
           public void onChildMoved(DataSnapshot dataSnapshot, String s) {

           }

           @Override
           public void onCancelled(DatabaseError databaseError) {

           }
       });

        return spacecrafts;
    }
}
(c). CustomAdapter.java

This is our adapter class. It derives from BaseAdapter.

No. Responsibility
1. This class will maintain a Context object that will be used to during layout inflation. Furthermore we declare an ArrayList of Spacecrafts that will be bound to our GridView.
2. Receive a Context and ArrayList of Spacecrafts from outside and assign them to our local instance fields.
3. Return data list count,Item and Item Identifier.
4. Inflate our model.xml layout and return it as a View when the getView() is called.
5. Listen to the inflated View click event and open our Master activity.
6. Pass the clicked spacecraft's details to the Detail Activity.
package com.tutorials.hp.firebasegridviewmdetail.m_UI;

import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.tutorials.hp.firebasegridviewmdetail.DetailActivity;
import com.tutorials.hp.firebasegridviewmdetail.R;
import com.tutorials.hp.firebasegridviewmdetail.m_Model.Spacecraft;

import java.util.ArrayList;

/
 * 1. where WE INFLATE OUR MODEL LAYOUT INTO VIEW ITEM
 * 2. THEN BIND DATA
 */
public class CustomAdapter extends BaseAdapter {
    Context c;
    ArrayList<Spacecraft> spacecrafts;

    public CustomAdapter(Context c, ArrayList<Spacecraft> spacecrafts) {
        this.c = c;
        this.spacecrafts = spacecrafts;
    }

    @Override
    public int getCount() {
        return spacecrafts.size();
    }

    @Override
    public Object getItem(int position) {
        return spacecrafts.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(convertView==null)
        {
            convertView= LayoutInflater.from(c).inflate(R.layout.model,parent,false);
        }

        TextView nameTxt= (TextView) convertView.findViewById(R.id.nameTxt);
        TextView propTxt= (TextView) convertView.findViewById(R.id.propellantTxt);
        TextView descTxt= (TextView) convertView.findViewById(R.id.descTxt);

        final Spacecraft s= (Spacecraft) this.getItem(position);

        nameTxt.setText(s.getName());
        propTxt.setText(s.getPropellant());
        descTxt.setText(s.getDescription());

        convertView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //OPEN DETAIL
                openDetailActivity(s.getName(),s.getDescription(),s.getPropellant());
            }
        });

        return convertView;
    }

    //OPEN DETAIL ACTIVITY
    private void openDetailActivity(String...details)
    {
        Intent i=new Intent(c,DetailActivity.class);

        i.putExtra("NAME_KEY",details[0]);
        i.putExtra("DESC_KEY",details[1]);
        i.putExtra("PROP_KEY",details[2]);

        c.startActivity(i);
    }
}
(d). SecondActivity.java

This is our DetailActivity. It will show the details of our Spacecraft.

Here's it's responsibilities and how it works:

No. Responsibility
1. Maintain three TextView objects as private instance fields that will be used to show Spacecraft details.
2. Override the onCreate() method. Call the super class version of onCreate() as well.
3. Inflate the activity_detail via the setContentView() to a View object and set it as the detail Activity's main UI.
4. Find the toolbar from activity_detail and set it as the actionbar of our SecondActivity.
5. Find TextViews defined in the content_detail.xml and assign them to our local TextView objects.
6. Retrieve the Intent assoicated with our SecondActivity via the getIntent() call.
7. Obtain name, description and propellant of our Spacecraft via the getExtras() method calls of our Intent.Then set those values to our TextView objects.
package com.tutorials.hp.firebasegridviewmdetail;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.TextView;

public class DetailActivity extends AppCompatActivity {

    TextView nameTxt,descTxt, propTxt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);

        nameTxt = (TextView) findViewById(R.id.nameDetailTxt);
        descTxt= (TextView) findViewById(R.id.descDetailTxt);
        propTxt = (TextView) findViewById(R.id.propellantDetailTxt);

        //get intent
        Intent i=this.getIntent();

        //RECEIVE DATA
        String name=i.getExtras().getString("NAME_KEY");
        String desc=i.getExtras().getString("DESC_KEY");
        String propellant=i.getExtras().getString("PROP_KEY");

        //BIND DATA
        nameTxt.setText(name);
        descTxt.setText(desc);
        propTxt.setText(propellant);

        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
    }
}
(e). MainActivity.java

This is our MainActivity. Our project has two activities and this is the main one. It will be the one launched when we launch our application.

It is also our Master View and will contain a grid of Spacecraft objects.

No. Responsibility
1. It will maintain a couple of objects as instance fields including: DatabaseReference,FirebaseHelper,CustomAdapter, GridView and three EditTexts.
2. Define a method to instantiate our Dialog object, set it's title, set its ConteView and finally show it.This dialog is our input dialog with edittexts and save/retrieve buttons.
3. Search all the input widgets defined in input_dialog.xml and assign them to their respective instance objects.These include EditTexts and Buttons.
4. Listen to Save button click events, then obtain edittext values, assign those values to a Spacecraft object and with the help of FirebaseHelper instance send that object to Firebase realtime database.
5. Override the onCreate() method,call it's super equivalence.
6. Find Toolbar in our layout and use it as our actionbar.
7. Get FirebaseDatabase instance then it's reference and pass it to our FirebaseHelper constructor.
8. Instantiate CustomAdapter, find Gridview from our layout, then assign the adapter to the Gridview.
9. Listen to FAB button click event and show the input dialog.
package com.tutorials.hp.firebasegridviewmdetail;

import android.app.Dialog;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.EditText;
import android.widget.GridView;
import android.widget.Toast;

import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.tutorials.hp.firebasegridviewmdetail.m_FireBase.FirebaseHelper;
import com.tutorials.hp.firebasegridviewmdetail.m_Model.Spacecraft;
import com.tutorials.hp.firebasegridviewmdetail.m_UI.CustomAdapter;

/*
1.INITIALIZE FIREBASE DB
2.INITIALIZE UI
3.DATA INPUT
 */
public class MainActivity extends AppCompatActivity {

    DatabaseReference db;
    FirebaseHelper helper;
    CustomAdapter adapter;
    GridView gv;
    EditText nameEditTxt,propTxt,descTxt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        gv= (GridView) findViewById(R.id.gv);

        //INITIALIZE FIREBASE DB
        db= FirebaseDatabase.getInstance().getReference();
        helper=new FirebaseHelper(db);

        //ADAPTER
        adapter=new CustomAdapter(this,helper.retrieve());
        gv.setAdapter(adapter);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                displayInputDialog();
            }
        });
    }

    //DISPLAY INPUT DIALOG
    private void displayInputDialog()
    {
        Dialog d=new Dialog(this);
        d.setTitle("Save To Firebase");
        d.setContentView(R.layout.input_dialog);

        nameEditTxt= (EditText) d.findViewById(R.id.nameEditText);
        propTxt= (EditText) d.findViewById(R.id.propellantEditText);
        descTxt= (EditText) d.findViewById(R.id.descEditText);
        Button saveBtn= (Button) d.findViewById(R.id.saveBtn);

        //SAVE
        saveBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //GET DATA
                String name=nameEditTxt.getText().toString();
                String propellant=propTxt.getText().toString();
                String desc=descTxt.getText().toString();

                //SET DATA
                Spacecraft s=new Spacecraft();
                s.setName(name);
                s.setPropellant(propellant);
                s.setDescription(desc);

                //SIMPLE VALIDATION
                if(name != null && name.length()>0)
                {
                    //THEN SAVE
                    if(helper.save(s))
                    {
                        //IF SAVED CLEAR EDITXT
                        nameEditTxt.setText("");
                        propTxt.setText("");
                        descTxt.setText("");
                        adapter=new CustomAdapter(MainActivity.this,helper.retrieve());
                        gv.setAdapter(adapter);
                    }
                }else
                {
                    Toast.makeText(MainActivity.this, "Name Must Not Be Empty", Toast.LENGTH_SHORT).show();
                }
            }
        });

        d.show();
    }
}

7. AndroidManifest.xml

Finally add internet permission in your AndroidManifest.xml as we will be accessing internet:

<manifest>
....
    <uses-permission android:name="android.permission.INTERNET" />
....
</manifest>

And that's it.

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