安卓Activity的onkeydown事件没有执行是怎么回事？

Question

之前在4.2版本写的时候可以执行，搬到4.4后就不行了，log发现根本没有执行那一步

public boolean onKeyDown(int keyCode, KeyEvent event) {
if(keyCode==KeyEvent.KEYCODE_BACK){
AlertDialog.Builder alertDialog=new AlertDialog.Builder(MainActivity.this);
alertDialog.setTitle("温馨提示");
alertDialog.setMessage("确定要退出应用吗？");
alertDialog.setPositiveButton("确定",new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
MainActivity.this.finish();
}
});
alertDialog.setNegativeButton("取消", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub

            }
            });
            alertDialog.show();
            }
    return false;
}

Answer 1

没有return true吧