View.OnKeyListener曾为我的活动工作过一次，不再工作了

Question

I have an Activity that implemented View.OnKeyListener so that it could catch when the user hit the back button and would pop up a dialog. Previously, it worked just fine. Recently, however, it has stopped working and the app would just pretend that there was no onKey method to catch the Back button. I can't seem to figure out why, as I've barely touched the onKey method since I made the changes. I tried just using OnBackPressed() instead, but that didn't solve anything and in fact created weird and unpredictable behavior. Can anyone help me figure out why it seems like my app is letting the system take the reigns on the back button?

Here's the important parts of my implementation:

import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.SherlockFragmentActivity;
import com.actionbarsherlock.view.Menu;
import com.actionbarsherlock.view.MenuItem;
import com.actionbarsherlock.view.MenuInflater;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.KeyEvent;
import android.view.View;

public class NagTasksAddTasksActivity extends SherlockFragmentActivity implements View.OnKeyListener {
    //various parameters
    public void onCreate(Bundle savedInstanceBundle)
    {
        super.onCreate(savedInstanceBundle);
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getBaseContext());
        String setTheme = prefs.getString("themeselect", "Dark Overflow");
        if (setTheme.toLowerCase().contentEquals("dark overflow")){
            setTheme(R.style.Theme_Sherlock_ForceOverflow);
        } else if (setTheme.toLowerCase().contentEquals("light overflow")){
            setTheme(R.style.Theme_Sherlock_Light_ForceOverflow);
            isDarkThemeUsed = false;
        } else if (setTheme.toLowerCase().contentEquals("dark menu")){
            setTheme(R.style.Theme_Sherlock);
        } else if (setTheme.toLowerCase().contentEquals("light menu")){
            setTheme(R.style.Theme_Sherlock_Light);
            isDarkThemeUsed = false;
        }
        setContentView(R.layout.createtasklayout);
        ActionBar actionBar = getSupportActionBar();
        setTitle(R.string.newTask);

    }
    ...
    @Override
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK)
        {
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setCancelable(true);
            builder.setTitle(R.string.wait);
            builder.setMessage(R.string.confirmbackkey);
            builder.setPositiveButton(R.string.save, new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    //stuff
                    dialog.dismiss();
                }
            });
            builder.setNegativeButton(R.string.discard, new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    AlertDialog.Builder subBuilder = new AlertDialog.Builder(getParent());
                    subBuilder.setCancelable(true);
                    subBuilder.setTitle(R.string.wait);
                    subBuilder.setMessage(R.string.confirmdiscard);
                    subBuilder.setPositiveButton(R.string.yes, new DialogInterface.OnClickListener() {

                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            //more stuff
                            dialog.dismiss();
                        }
                    });
                    subBuilder.setNegativeButton(R.string.no, new DialogInterface.OnClickListener() {

                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            dialog.cancel();
                        }
                    });
                    dialog.dismiss();
                    subBuilder.create().show();
                }
            });
            builder.setNeutralButton(R.string.cancel, new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    dialog.cancel();
                }
            });
            builder.create().show();
            return true;
        }
        return false;
    }
}

Answer 1

Another way to catch the back button is to use the dispatchKeyEvent method in the Activity (you don't need to implement View.OnKeyListener). This seems to work for me every time.

public class HomeActivity extends Activity
{
...

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) 
    {
        int action = event.getAction();
        int keyCode = event.getKeyCode();
        switch (keyCode) 
        {
            case KeyEvent.KEYCODE_BACK:
                if (action == KeyEvent.ACTION_DOWN)
                {
                    Log.v("myApp", "Back button pressed.");
                    return true;
                }
            default:
                return false;
        }
        return false;
    }
}

Answer 2

Try removing the return true under builder.create().show(); and change the return false into return true and see if it works. this should let them all to return results when a KeyEvent is initialized.

Answer 3

The simplest way to do this is to override OnBackPressed and fill in the code you want to have happen when someone presses the back button.

just make sure you delete the super.OnBackPressed line.