在中国，大多数App会通过“点击两次”确认退出:

boolean doubleBackToExitPressedOnce = false;

@Override
public void onBackPressed() {
    if (doubleBackToExitPressedOnce) {
        super.onBackPressed();
        return;
    }

    this.doubleBackToExitPressedOnce = true;
    Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();

    new Handler().postDelayed(new Runnable() {

        @Override
        public void run() {
            doubleBackToExitPressedOnce=false;                       
        }
    }, 2000);
} 

在中国，大多数App会通过“点击两次”确认退出:

boolean doubleBackToExitPressedOnce = false;

@Override
public void onBackPressed() {
    if (doubleBackToExitPressedOnce) {
        super.onBackPressed();
        return;
    }

    this.doubleBackToExitPressedOnce = true;
    Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();

    new Handler().postDelayed(new Runnable() {

        @Override
        public void run() {
            doubleBackToExitPressedOnce=false;                       
        }
    }, 2000);
} 

另一种选择是在第一次回按时显示一个Toast/Snackbar，要求再次返回退出，这比显示一个AlertDialog来确认用户是否想退出应用程序要少得多。

你可以使用DoubleBackPress Android库来实现这一点，只需几行代码。示例GIF显示类似的行为。

首先，将依赖项添加到应用程序中:

dependencies {
    implementation 'com.github.kaushikthedeveloper:double-back-press:0.0.1'
}

接下来，在您的活动中，实现所需的行为。

// set the Toast to be shown on FirstBackPress (ToastDisplay - builtin template)
// can be replaced by custom action (new FirstBackPressAction{...})
FirstBackPressAction firstBackPressAction = new ToastDisplay().standard(this);

// set the Action on DoubleBackPress
DoubleBackPressAction doubleBackPressAction = new DoubleBackPressAction() {
    @Override
    public void actionCall() {
        // TODO : Exit the application
        finish();
        System.exit(0);
    }
};

// setup DoubleBackPress behaviour : close the current Activity
DoubleBackPress doubleBackPress = new DoubleBackPress()
        .withDoublePressDuration(3000)     // msec - wait for second back press
        .withFirstBackPressAction(firstBackPressAction)
        .withDoubleBackPressAction(doubleBackPressAction);

最后，将此设置为背压的行为。

@Override
public void onBackPressed() {
    doubleBackPress.onBackPressed();
}

我更喜欢双击后退按钮退出，而不是退出对话框。

在这个解决方案中，当第一次返回时，它会显示一个吐司，警告另一个回按将关闭应用程序。在这个例子中，不到4秒。

private Toast toast;
private long lastBackPressTime = 0;

@Override
public void onBackPressed() {
  if (this.lastBackPressTime < System.currentTimeMillis() - 4000) {
    toast = Toast.makeText(this, "Press back again to close this app", 4000);
    toast.show();
    this.lastBackPressTime = System.currentTimeMillis();
  } else {
    if (toast != null) {
    toast.cancel();
  }
  super.onBackPressed();
 }
}

令牌来自:http://www.androiduipatterns.com/2011/03/back-button-behavior.html

Just put this code in your first activity 

@Override
    public void onBackPressed() {
        if (drawerLayout.isDrawerOpen(GravityCompat.END)) {
            drawerLayout.closeDrawer(GravityCompat.END);
        }
        else {
// if your using fragment then you can do this way
            int fragments = getSupportFragmentManager().getBackStackEntryCount();
            if (fragments == 1) {
new AlertDialog.Builder(this)
           .setMessage("Are you sure you want to exit?")
           .setCancelable(false)
           .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                    finish();
               }
           })
           .setNegativeButton("No", null)
           .show();


            } else {
                if (getFragmentManager().getBackStackEntryCount() > 1) {
                    getFragmentManager().popBackStack();
                } else {

           super.onBackPressed();
                }
            }
        }
    }

@Override
public void onBackPressed() {
    new AlertDialog.Builder(this)
           .setMessage("Are you sure you want to exit?")
           .setCancelable(false)
           .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                   ExampleActivity.super.onBackPressed();
               }
           })
           .setNegativeButton("No", null)
           .show();
}