java - How to resume Android Activity programmatically from background

Question

Situation:

1. Let's say I have currently working launched application Activity A.
2. After some time I am pressing "Home" button. Application A goes to background.
3. At this time, I am starting to use another app B - youtube for example or etc.
4. Something happens (doesn't matter what in this context, let's say timer finished calculating time) in the application A which currently is minimized to background.
5. On the event occurrence, application A activity automatically resumes from background.

Question:

How to accomplish step 5? Basically I need to know how to resume application from background programmatically.

I tried to launch intent to "restart" my application activity but it didn't worked:

Intent intent = new Intent(context, MainActivity.class);
            intent.setAction(Intent.ACTION_MAIN);
            intent.addCategory(Intent.CATEGORY_LAUNCHER);
            context.startActivity(intent);

My manifest file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.taxti"
    android:versionCode="43"
    android:versionName="1.5.3" >     

    <uses-sdk
        android:minSdkVersion="13"
        android:targetSdkVersion="21" />

    <permission
        android:name="com.example.taxti.permission.MAPS_RECEIVE"
        android:protectionLevel="signature" />

    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true" />

    <uses-permission android:name="com.example.taxti.permission.MAPS_RECEIVE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.GET_ACCOUNTS" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />       
    <permission android:name="com.taxti.permission.C2D_MESSAGE"
                android:protectionLevel="signature" />
    <uses-permission android:name="com.taxti.permission.C2D_MESSAGE" />     
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />   
    <uses-permission android:name="android.permission.CALL_PHONE" />  
    <uses-permission android:name="android.permission.EXPAND_STATUS_BAR" />
    <uses-permission android:name="android.permission.CLEAR_APP_CACHE" />

    <application
        android:allowBackup="true"        
        android:icon="@drawable/ic_launcher"
        android:hardwareAccelerated="true"
        android:label="@string/app_name"
        android:name="com.taxti.Globals"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.taxti.InitialActivity"
            android:label="@string/app_name"
            android:windowSoftInputMode="adjustPan"
            android:screenOrientation="sensorLandscape"
            android:theme="@style/MyTheme" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.taxti.MainActivity"
            android:label="@string/app_name"
            android:launchMode="singleTop"
            android:windowSoftInputMode="adjustPan"
            android:screenOrientation="sensorLandscape"
            android:theme="@style/MyTheme">
        </activity>

        <service android:name=".MainActivityForegroundService" />

        <intent-filter>
                <action android:name="android.net`enter code here`.conn.CONNECTIVITY_CHANGE" />                
        </intent-filter>

       <intent-filter>
            <action android:name="android.intent.action.CALL_PRIVILEGED" />
            <category android:name="android.intent.category.DEFAULT" />     
            <action android:name="android.intent.action.DIAL" />
            <action android:name="android.intent.action.CALL_BUTTON" />     
            <category android:name="android.intent.category.BROWSABLE" />           
            <data android:scheme="tel" />
       </intent-filter>

        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />
        <meta-data
            android:name="com.google.android.maps.v2.API_KEY"
            android:value="xxxx" />             
        <uses-library android:name="com.google.android.maps" />

        <receiver
            android:name=".GcmBroadcastReceiver"
            android:permission="com.google.android.c2dm.permission.SEND" >   
            <intent-filter>
                <action android:name="com.google.android.c2dm.intent.RECEIVE" />               
                <category android:name="com.taxti" />
            </intent-filter>

        </receiver>

    </application>

</manifest>

Answer 1

In order to bring your app to the foreground, you must call startActivity() from another context (either a Service or a BroadcastReceiver). Just calling startActivity() from within an Activity won't bring your app to the foreground.

You don't need the ACTION and CATEGORY in your Intent, but you do need to set Intent.FLAG_ACTIVITY_NEW_TASK.