Android 重写返回键

下面是几种重写返回键 的方法

//第一种public boolean onKeyDown(int keyCode, KeyEvent event) {// 按下键盘上返回按钮  if (keyCode == KeyEvent.KEYCODE_BACK) {    new AlertDialog.Builder(this)    .setMessage("确定退出系统吗？")    .setNegativeButton("取消",     new DialogInterface.OnClickListener() {     public void onClick(DialogInterface dialog,     int which) {       }     })    .setPositiveButton("确定",     new DialogInterface.OnClickListener() {       public void onClick(DialogInterface dialog,     int whichButton) {   finish();       }     }).show();    return true;  } else {    return super.onKeyDown(keyCode, event);}  }     //直接退出程序@Override protected void onDestroy() {      super.onDestroy();      // 或者下面这种方式      //System.exit(0);      //建议用这种      android.os.Process.killProcess(android.os.Process.myPid());}//第二种@Override public boolean onKeyDown(int keyCode, KeyEvent event) {            if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {                     //TODO something                    return true;              }              return super.onKeyDown(keyCode, event); }//第三种@Override public void onBackPressed() {           //TODO something          super.onBackPressed(); }