如何从活动中访问方法并将其用于Android中的另一个活动？

Question

I have the first class named iHave

public class iHave extends ActionBarActivity
{   

//below is the instance for calling the method from the other activity. 
(The name of the other activity is **iThank**)

**iThank thankYou = new iThank();**

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

    Button button = (Button) findViewById(R.id.button);

    button.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            **//this is the method I want to access from iThank class** **strong text**
            thankYou.display();
        }
    });       
} 

//The Next class is "iThank"

public class iThank extends ActionBarActivity
{

 @Override

protected void onCreate(Bundle savedInstanceState)
{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_i_thank);

        txtThank = (TextView) findViewById(R.id.textView3);

    //this is the method I want to access/use from iHave Activity 
    public void display()
    {
        txtThank.setText ("Shine");
    }
}

How can I use the method " public void display() " of iThank activity to the "iHave" activity? It always gives me an error of NullPointerException . Please help. Thank you very much!

Answer 1

How can I access a method from an activity and use it into another activity in Android?

By creating object for other to access method from Activity is right way.

Use LocalBroadcastManager for communicating between application components.

1. Send broadcast from iHave on Button click:

@Override
   public void onClick(View v)
     {
       Intent intent = new Intent("DISPLAY_EVENT");
       LocalBroadcastManager.getInstance(v.getContext()).sendBroadcast(intent);
     }

2. Register LocalBroadcastManager in iThank Activity:

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
    LocalBroadcastManager.getInstance(this).registerReceiver(ReceiveMessage,
            new IntentFilter("DISPLAY_EVENT"));
}

3. Create BroadcastReceiver object and call display() method in iThank Activity:

private BroadcastReceiver ReceiveMessage = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            // TODO Auto-generated method stub
             display();
        }
    };

Also add null check in display method for TextView:

public void display()
{   
   if(txtThank !=null)
    txtThank.setText ("Shine");
}

Answer 2

Please don't to this, it is not how activities are intended to work. You might want to have a look over the Activities Developer Guide to get started. If you want to launch a new activity (eg iThank ) from the current foreground activity (eg iHave ), you never instantiate the class yourself directly and always launch it using an intent . If you have data to pass along (such as a message to display), it needs to be bundled along with the intent as an extra (see same link).

Activities should never call methods on each other directly, because this requires them to have references to each other. The framework manages the life cycle of each activity independently, and those references can lead to leaks.