How to Make Android Apps 18

Posted by Derek Banas on Dec 20, 2014 in Android Development Tutorial | 0 comments

In this part of my Android tutorial we cover how to use Intent Services, Broadcasts, Broadcast Receivers, Intent Filters and how to download, save and read files.

I did my best to keep all of the code separated so that you can easily copy and paste out the functionality you need with your Android apps. All of the code follows the video with a ton of comments.

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Code From the Video

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Download File"
        android:id="@+id/startServiceButton"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:onClick="startFileService"/>

    <EditText
        android:layout_width="match_parent"
        android:layout_height="350dp"
        android:inputType="textMultiLine"
        android:ems="10"
        android:id="@+id/downloadedEditText"
        android:layout_below="@+id/startServiceButton"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="41dp" />

</RelativeLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"

android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Download File"

android:id="@+id/startServiceButton"

android:layout_alignParentTop="true"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:onClick="startFileService"/>

<EditText

android:layout_width="match_parent"

android:layout_height="350dp"

android:inputType="textMultiLine"

android:ems="10"

android:id="@+id/downloadedEditText"

android:layout_below="@+id/startServiceButton"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_marginTop="41dp" />

</RelativeLayout>

MainActivity.java

package com.newthinktank.derekbanas.serviceex;

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

// IntentService : Uses an intent to start a background service so as not to disturb the UI
// Android Broadcast : Triggers an event that a BroadcastReceiver can act on
// BroadcastReceiver : Acts when a specific broadcast is made

public class MainActivity extends Activity {

    EditText downloadedEditText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        downloadedEditText = (EditText) findViewById(R.id.downloadedEditText);

        // Allows use to track when an intent with the id TRANSACTION_DONE is executed
        // We can call for an intent to execute something and then tell use when it finishes
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(FileService.TRANSACTION_DONE);

        // Prepare the main thread to receive a broadcast and act on it
        registerReceiver(downloadReceiver, intentFilter);
    }

    public void startFileService(View view) {

        // Create an intent to run the IntentService in the background
        Intent intent = new Intent(this, FileService.class);

        // Pass the URL that the IntentService will download from
        intent.putExtra("url", "https://www.newthinktank.com/wordpress/lotr.txt");

        // Start the intent service
        this.startService(intent);

    }

    // Is alerted when the IntentService broadcasts TRANSACTION_DONE
    private BroadcastReceiver downloadReceiver = new BroadcastReceiver() {

        // Called when the broadcast is received
        @Override
        public void onReceive(Context context, Intent intent) {

            Log.e("FileService", "Service Received");

            showFileContents();

        }
    };

    // Will read our local file and put the text in the EditText
    public void showFileContents(){

        // Will build the String from the local file
        StringBuilder sb;

        try {
            // Opens a stream so we can read from our local file
            FileInputStream fis = this.openFileInput("myFile");

            // Gets an input stream for reading data
            InputStreamReader isr = new InputStreamReader(fis, "UTF-8");

            // Used to read the data in small bytes to minimize system load
            BufferedReader bufferedReader = new BufferedReader(isr);

            // Read the data in bytes until nothing is left to read
            sb = new StringBuilder();
            String line;
            while ((line = bufferedReader.readLine()) != null) {
                sb.append(line).append("\n");
            }

            // Put downloaded text into the EditText
            downloadedEditText.setText(sb.toString());


        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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package com.newthinktank.derekbanas.serviceex;

import android.app.Activity;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import android.os.Bundle;

import android.util.Log;

import android.view.View;

import android.widget.EditText;

import java.io.BufferedReader;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.UnsupportedEncodingException;

// IntentService : Uses an intent to start a background service so as not to disturb the UI

// Android Broadcast : Triggers an event that a BroadcastReceiver can act on

// BroadcastReceiver : Acts when a specific broadcast is made

public class MainActivity extends Activity {

EditText downloadedEditText;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

downloadedEditText = (EditText) findViewById(R.id.downloadedEditText);

// Allows use to track when an intent with the id TRANSACTION_DONE is executed

// We can call for an intent to execute something and then tell use when it finishes

IntentFilter intentFilter = new IntentFilter();

intentFilter.addAction(FileService.TRANSACTION_DONE);

// Prepare the main thread to receive a broadcast and act on it

registerReceiver(downloadReceiver, intentFilter);

}

public void startFileService(View view) {

// Create an intent to run the IntentService in the background

Intent intent = new Intent(this, FileService.class);

// Pass the URL that the IntentService will download from

intent.putExtra("url", "https://www.newthinktank.com/wordpress/lotr.txt");

// Start the intent service

this.startService(intent);

}

// Is alerted when the IntentService broadcasts TRANSACTION_DONE

private BroadcastReceiver downloadReceiver = new BroadcastReceiver() {

// Called when the broadcast is received

@Override

public void onReceive(Context context, Intent intent) {

Log.e("FileService", "Service Received");

showFileContents();

}

};

// Will read our local file and put the text in the EditText

public void showFileContents(){

// Will build the String from the local file

StringBuilder sb;

try {

// Opens a stream so we can read from our local file

FileInputStream fis = this.openFileInput("myFile");

// Gets an input stream for reading data

InputStreamReader isr = new InputStreamReader(fis, "UTF-8");

// Used to read the data in small bytes to minimize system load

BufferedReader bufferedReader = new BufferedReader(isr);

// Read the data in bytes until nothing is left to read

sb = new StringBuilder();

String line;

while ((line = bufferedReader.readLine()) != null) {

sb.append(line).append("\n");

}

// Put downloaded text into the EditText

downloadedEditText.setText(sb.toString());

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (UnsupportedEncodingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

FileService.java

package com.newthinktank.derekbanas.serviceex;

import android.app.IntentService;
import android.content.Context;
import android.content.Intent;
import android.util.Log;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

// We use an IntentService to handle long running processes off the UI thread
// Any new requests will wait for the 1st to end and it can't be interrupted

public class FileService extends IntentService {

    // Used to identify when the IntentService finishes
    public static final String TRANSACTION_DONE = "com.newthinktank.TRANSACTION_DONE";

    // Validates resource references inside Android XML files
    public FileService() {
        super(FileService.class.getName());
    }


    public FileService(String name) {
        super(name);
    }

    @Override
    protected void onHandleIntent(Intent intent) {

        Log.e("FileService", "Service Started");

        // Get the URL for the file to download
        String passedURL = intent.getStringExtra("url");

        downloadFile(passedURL);

        Log.e("FileService", "Service Stopped");

        // Broadcast an intent back to MainActivity when file is downloaded
        Intent i = new Intent(TRANSACTION_DONE);
        FileService.this.sendBroadcast(i);

    }

    protected void downloadFile(String theURL) {

        // The name for the file we will save data to
        String fileName = "myFile";

        try{

            // Create an output stream to write data to a file (private to everyone except our app)
            FileOutputStream outputStream = openFileOutput(fileName, Context.MODE_PRIVATE);

            // Get File
            URL fileURL = new URL(theURL);

            // Create a connection we can use to read data from a url
            HttpURLConnection urlConnection = (HttpURLConnection) fileURL.openConnection();

            // We are using the GET method
            urlConnection.setRequestMethod("GET");

            // Set that we want to allow output for this connection
            urlConnection.setDoOutput(true);

            // Connect to the url
            urlConnection.connect();

            // Gets an input stream for reading data
            InputStream inputStream = urlConnection.getInputStream();

            // Define the size of the buffer
            byte[] buffer = new byte[1024];
            int bufferLength = 0;

            // read reads a byte of data from the stream until there is nothing more
            while ( (bufferLength = inputStream.read(buffer)) > 0 ){

                // Write the data received to our file
                outputStream.write(buffer, 0, bufferLength);

            }

            // Close our connection to our file
            outputStream.close();

            // Get File Done

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

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package com.newthinktank.derekbanas.serviceex;

import android.app.IntentService;

import android.content.Context;

import android.content.Intent;

import android.util.Log;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.URL;

// We use an IntentService to handle long running processes off the UI thread

// Any new requests will wait for the 1st to end and it can't be interrupted

public class FileService extends IntentService {

// Used to identify when the IntentService finishes

public static final String TRANSACTION_DONE = "com.newthinktank.TRANSACTION_DONE";

// Validates resource references inside Android XML files

public FileService() {

super(FileService.class.getName());

}

public FileService(String name) {

super(name);

}

@Override

protected void onHandleIntent(Intent intent) {

Log.e("FileService", "Service Started");

// Get the URL for the file to download

String passedURL = intent.getStringExtra("url");

downloadFile(passedURL);

Log.e("FileService", "Service Stopped");

// Broadcast an intent back to MainActivity when file is downloaded

Intent i = new Intent(TRANSACTION_DONE);

FileService.this.sendBroadcast(i);

}

protected void downloadFile(String theURL) {

// The name for the file we will save data to

String fileName = "myFile";

try{

// Create an output stream to write data to a file (private to everyone except our app)

FileOutputStream outputStream = openFileOutput(fileName, Context.MODE_PRIVATE);

// Get File

URL fileURL = new URL(theURL);

// Create a connection we can use to read data from a url

HttpURLConnection urlConnection = (HttpURLConnection) fileURL.openConnection();

// We are using the GET method

urlConnection.setRequestMethod("GET");

// Set that we want to allow output for this connection

urlConnection.setDoOutput(true);

// Connect to the url

urlConnection.connect();

// Gets an input stream for reading data

InputStream inputStream = urlConnection.getInputStream();

// Define the size of the buffer

byte[] buffer = new byte[1024];

int bufferLength = 0;

// read reads a byte of data from the stream until there is nothing more

while ( (bufferLength = inputStream.read(buffer)) > 0 ){

// Write the data received to our file

outputStream.write(buffer, 0, bufferLength);

}

// Close our connection to our file

outputStream.close();

// Get File Done

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.newthinktank.derekbanas.serviceex" >

    <!-- We need permission to access the internet -->
    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        <!-- Declare the service -->
        <service
            android:name=".FileService"
            android:exported="false" />

    </application>

</manifest>

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.newthinktank.derekbanas.serviceex" >

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

<application

android:allowBackup="true"

android:icon="@drawable/ic_launcher"

android:label="@string/app_name"

android:theme="@style/AppTheme" >

<activity

android:name=".MainActivity"

android:label="@string/app_name" >

<intent-filter>

</intent-filter>

</activity>

<service

android:name=".FileService"

android:exported="false" />

</application>

</manifest>

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How to Make Android Apps 18

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