Android按返回键不退出

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
       moveTaskToBack(true);
       return true;
   }
return super.onKeyDown(keyCode, event);

}

Move the task containing this activity to the back of the activity stack. The activity's order within the task is unchanged.

Parameters
nonRoot  If false then this only works if the activity is the root of a task; if true it will work for any activity in a task. 

Returns
If the task was moved (or it was already at the back) true is returned, else false.