android中连续点击返回键退出整个应用的实现

package com.zp.demo; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.KeyEvent; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast; public class MainActivity extends Activity { private long firstClick; private Button button; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); button = (Button)findViewById(R.id.button); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(); intent.setClass(MainActivity.this, SecondActivity.class); startActivity(intent); } }); MyApplication.getInstance().addActivity(this); } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { if(keyCode == KeyEvent.KEYCODE_BACK) { long secondClick = System.currentTimeMillis(); if(secondClick - firstClick > 1000) { Toast.makeText(MainActivity.this, "再次点击退出", Toast.LENGTH_SHORT).show(); firstClick = secondClick; return true; }else{ MyApplication.getInstance().exitApp(); return true; } } return super.onKeyDown(keyCode, event); } }