Android中按两次返回退出应用

一、使用系统秒数

public class MainActivity extends AppCompatActivity {

    private long exitTime = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    //系统方法
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event){
        if(keyCode==KeyEvent.KEYCODE_BACK){
            exit();
            return false;
        }
        return super.onKeyDown(keyCode,event);
    }

    private void exit(){
        if((System.currentTimeMillis()-exitTime)>2000) {
            Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        }else{
            finish();
            System.exit(0);
        }
    }
}

二、使用Handler

public class MainActivity extends AppCompatActivity {

    private boolean isExit = false;
    
    Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            isExit = false;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            exit();
            return false;
        }
        return super.onKeyDown(keyCode, event);
    }

    private void exit() {
        if (!isExit) {
            isExit = true;
            Toast.makeText(getApplicationContext(), "再按一次退出程序",Toast.LENGTH_SHORT).show();
            mHandler.sendEmptyMessageDelayed(0, 2000);
        } else {
            finish();
            System.exit(0);
        }
    }
}