private int back = 0;//===============back两次退出=====================@Overridepublic boolean onCreateOptionsMenu(Menu menu) {//必要的改变menu.add(0, 2, 2, "退出");return super.onCreateOptionsMenu(menu);}@Overridepublic boolean onOptionsItemSelected(MenuItem item) {switch (item.getItemId()) {case 2:Myback();break;}return super.onOptionsItemSelected(item);}@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {//两次back退出if (keyCode == KeyEvent.KEYCODE_BACK) {back++;switch (back) {case 1:Toast.makeText(MainActivity.this, "再按一次退出",Toast.LENGTH_SHORT).show();break;case 2:back = 0;// 初始化back值Myback();break;}return true;// 设置成false让back失效 ，true表示 不失效} else {return super.onKeyDown(keyCode, event);}}public void Myback() { // 关闭程序MainActivity.this.finish();android.os.Process.killProcess(android.os.Process.myPid());// 关闭进程}

private int tDifference = 2000;//等待的时间
private boolean isExit = false;   //状态
private Timer mTicker = null;//定义Timer时间器
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {// 两次back退出
if (keyCode == KeyEvent.KEYCODE_BACK) {
Myback();
return true;
} else {
return super.onKeyDown(keyCode, event);
}}public void Myback() { // 关闭程序
if(isExit){
MainActivity.this.finish();
android.os.Process.killProcess(android.os.Process.myPid());// 关闭进程
}else{
Toast.makeText(MainActivity.this, "再按一次退出", Toast.LENGTH_SHORT).show();
isExit = !isExit;
if(null == mTicker){
mTicker = new Timer();
}
mTicker.schedule(new TimerTask() {
@Override
public void run() {//改变标识
isExit = false;}
},tDifference );
}
}