Android：如何专门处理Back Press？

Question

Let me explain more detail.

First of all; I know that if user press back and returns the previous activity, the previous activity triggers onResume method properly. This is okay.

There is a root activity in my application and it's directing 4 different activities through the buttons. I want to learn, on which activity did user press back button? Is it possible to use something like Handler or similar?

Actually, I've found a solution verdantly. I've 4 different static Boolean vars an each one represents one Activity. Let me show in code:

public class MainActivity extends Activity { // This is root

    static Boolean activityA;
    static Boolean activityB;
    static Boolean activityC;
    static Boolean activityD;

    public void onClick(View v) {
        if(v == ActivitvyA) //of course psuedo 
             activityA = true
        //...there are similar controls
    }

    protected void onResume() {
        if(activitiyA) // If true, this means the user pressed back on ActivityA
    }

}

What do you think? Is there any diffent and effecient way?

Any helps would be great.

Answer 1

Basically, you want to know which activity the user is coming from when he lands on your root activity.

The best way I can see to carry this kind of information is to start your child activity using startActivityForResult .

public static final int CODE_A = 10;
public static final int CODE_B = 20;

public void goToA() {
  Intent i = new Intent(this,AActivity.class);
  startActivityForResult(i, CODE_A);
}

public void goToB() {
  Intent i = new Intent(this,BActivity.class);
  startActivityForResult(i, CODE_B);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
  if(resultCode==CODE_A) {
    // ...
  }
  else if(resultCode==CODE_B) {
    // ...
  }
}

Another way to do that is to store somewhere (for instance in a custom Application class) the last activity that had been visible to the user and update that in each activity's onPause method. Something like:

class MyApplication extends android.app.Application {
  public Class latestActivity;
}

class MyBaseActivity extends Activity {
  public void onPause() {
    ((MyApplication)getApplication()).latestActivity = this.getClass();
    super.onPause();
  }
}

Last way to do it is to store in your root activity the activity you have just launched.

class MyRootActivity extends Activity {
  private String latestUserAction;

  public void goToA() {
    latestUserAction = "goToA";
    startActivity(Intent.ACTION_VIEW, .........
  }

  // Don't forget to check that latestUserAction gets saved and restored when your activity is paused or stopped.
}

Answer 2

When you open your activities use startActivityForResult(intent, requestCode) and then.. You can override onBackPressed() in your activities by setting the activity name as a result..

@Override
public void onBackPressed() {
    super.onBackPressed();
    setResult(ActivityName);
}

then in your MainActivity check the result passed..