How to declare the activity in manifest file?

How to declare the activity in manifest file?

The activity must be declared in the manifest file in order to access by the system. The manifest file is an xml file included in the application and default known as AndroidManifest.xml.

Open the file from project and edit the xml to add the activity in file.

The activity is the child node of the application node. The multiple activities can specify by multiple nodes of activity. 

Each node of activity will specify the name of the activity to recognize by the system. One activity must be declare as the main activity.

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

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

    package="com.creativeandroidapps.creativeapp"

    android:versionCode="1"

    android:versionName="1.0" >

    //add the minsdkVersion to support backward compatibility

    <uses-sdk android:minSdkVersion="4" android:targetSdkVersion="15" />

    <application

        android:icon="@drawable/ic_launcher"  //change your app icon here

        android:label="@string/app_name" >    //change your app name here

        <activity       //main activity

            android:name=".creativeappActivity"

            android:label="@string/app_name" >

            <intent-filter>

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

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

            </intent-filter>

        </activity>

         <activity      //add another activity

            android:name=".ChildActivity"

            android:label="@string/app_name" >

          </activity>

    </application>

</manifest>

How to manage the activity state in android?

How to manage the activity state in android?

The activity could go for destruction during its lifecycle by the system. If the system has enough memory the system allows the activities in memory otherwise send the activity to destroy. When user navigates the activity back the system recreate the activity object without notice of user.

In this case the state of the activity is lost. To manage the activity state and data before destroy the onSaveInstanceState Method will be called. All the activity objects can be saved by implementing the callback method.

The data can be resume and process back on onResumeInstanceState method. 

Tutorial - Activity Life Cycle (Android)

What is Activity ? - Activity is an application component provides the screen to interact with user on the device. Activity class provides the methods to create and manage the windows on the screen.

Activity Life Cycle

An android application consist a set of multiple activities. An activity in android application provides the user interface or object to interact with the device. One of the activities of the application is the main activity. Each activity has its own lifecycle and an activity can start another activity to perform some actions and is able to create a chain of activities.

Each time a new activity starts, the previous activity is stopped, but the system preserves the activity in a stack (the "back stack"). When a new activity starts, it is pushed onto the back stack and takes user focus. The back stack abides to the basic "last in, first out" stack mechanism, so, when the user is done with the current activity and presses the Back button, it is popped from the stack (and destroyed) and the previous activity resumes.

The activity in the application will implement by extending the class by Activity class. The activity life cycle is processed by callback methods.

The following are the callback methods need to implement to handle the activity lifecycle.

public class CreativeActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // The activity is being created.

        //here we can do the – UI initialization, Background threads

      }
    @Override
    protected void onStart() {
        super.onStart();
        // The activity is about to become visible.
    }
    @Override
    protected void onResume() {
        super.onResume();
        // The activity has become visible (it is now "resumed").
    }
    @Override
    protected void onPause() {
        super.onPause();
        // Another activity is taking focus (this activity is about to be "paused").
    }
    @Override
    protected void onStop() {
        super.onStop();
        // The activity is no longer visible (it is now "stopped")
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        // The activity is about to be destroyed.
    }
}

How to finish the parent activity from child activity

finishing a parent activity  from child activity can be implement by starting the child activity using the startActivityForResult and implement the onActivityResult to process the result return by the child activity.

For Example if you have two activities ParentActivity and ChildActivity

Implement the following code in Parent Activity

/*start the child activity for a result*/

//bundle your stuff to pass data from parent activity to child activity

Bundle bundle = new Bundle();
bundle.putInt("category", 1);
Intent done = new Intent(ParentActivity.this, ChildActivity.class);

done.putExtras(bundle);

//start the activity for result

startActivityForResult(done,1);

Now implement the onActivityResult in parent activity

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) 
{
     super.onActivityResult(requestCode, resultCode, data);
     //matches the result code passed from ChildActivity
     if(resultCode == 0)
     {
                       //kill self
         ParentActivity.this.finish();
     }
}

Implement the following code in ChildActivity

@Override
    public void onStop()
    {
        super.onStop();
        this.setResult(0);
    }


@Override
    public void onDestroy()
    {
        super.onDestroy();
        this.setResult(0);
    }

Enjoy Creative Android Apps

How to set the Background of the Main View of Activity?

You can set the background of the activity main view using the following code

   //get the root view of the activity
 View view = this.getWindow().getDecorView();
   //set the background color to BLUE
 view.setBackgroundColor(Color.BLUE);

getDecorView() retrieve the top-level window decor view (containing the standard window frame/decorations and the client's content inside of that).

if you want to draw a image on the background then use

view.setBackgroundDrawable(getResources().getDrawable(R.drawable.bgimage));

The bgimage need to add in res->drawable-mdpi.

drawable-mdpi stores medium density pixel independence on your phone screen.