android 中back两种退出app的方法

连续点击退出app

• 思路:双击时间差小于某个定值触发事件
• 代码：

public class MainActivity extends AppCompatActivity {    private long lastTime=0; //记录上次点击的时间    @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&&event.getAction()==KeyEvent.ACTION_DOWN){            if((System.currentTimeMillis()-lastTime)>2000){            Toast.makeText(MainActivity.this, "在按一次退出程序", Toast.LENGTH_SHORT).show();              lastTime=System.currentTimeMillis();            }else {                System.exit(0);            }            return  true;        }        return super.onKeyDown(keyCode, event);    }}

单击弹出dialog退出app

• 单击back弹出dialog,强制禁止back取消dialog的消失

public class Main2Activity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main2);    }    @Override    public boolean onKeyDown(int keyCode, KeyEvent event) {        if (keyCode == KeyEvent.KEYCODE_BACK) {            AlertDialog exitDialog = new AlertDialog.Builder(this).create();            exitDialog.setTitle("系统提示");            exitDialog.setMessage("你确定要退出吗");            exitDialog.setButton(DialogInterface.BUTTON_POSITIVE, "确定", new DialogInterface.OnClickListener() {                @Override                public void onClick(DialogInterface dialog, int which) {                    finish();                }            });            exitDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "取消", new DialogInterface.OnClickListener() {                @Override                public void onClick(DialogInterface dialog, int which) {                    Toast.makeText(Main2Activity.this, "我已经取消了", Toast.LENGTH_SHORT).show();                }            });    //onKeyListener用于设置监听手机back键的操作            exitDialog.setOnKeyListener(new DialogInterface.OnKeyListener() {                @Override                public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {                    if (keyCode == KeyEvent.KEYCODE_BACK) {                        return true;// false时dialog会消失                    }                    return true;                }            });            exitDialog.show();        }        return super.onKeyDown(keyCode, event);    }}

验证

以上两种方法全部经过试验，可以拿来使用