selectDialog.setOnCancelListener(new OnCancelListener() {
        
        @Override
        public void onCancel(DialogInterface dialog) {
          // TODO Auto-generated method stub
      
            // Toast.makeText(getBaseContext(), "点击了back", Toast.LENGTH_SHORT).show();
        }
      });

selectDialog.setOnKeyListener(new OnKeyListener() {
        
        @Override
        public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {
          // TODO Auto-generated method stub
          if(keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount()==0)
          {
            dialog.dismiss();
          }
          return false;
        }
      });
　　public boolean dispatchKeyEvent(KeyEvent event)
  {
    
    switch(event.getKeyCode())
    {
    case KeyEvent.KEYCODE_BACK:      
      Toast.makeText(getBaseContext(), "点击了back", Toast.LENGTH_SHORT).show();
      break;
    default:
      break;
    }
    return super.dispatchKeyEvent(event);
  }