在Sudheesh B Nair的回答中有一些改进，我注意到它会等待处理程序，即使在立即按回两次，所以取消处理程序如下所示。我已经取消吐司也防止它显示后应用程序退出。

 boolean doubleBackToExitPressedOnce = false;
        Handler myHandler;
        Runnable myRunnable;
        Toast myToast;

    @Override
        public void onBackPressed() {
            if (doubleBackToExitPressedOnce) {
                myHandler.removeCallbacks(myRunnable);
                myToast.cancel();
                super.onBackPressed();
                return;
            }

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

            myHandler = new Handler();

            myRunnable = new Runnable() {

                @Override
                public void run() {
                    doubleBackToExitPressedOnce = false;
                }
            };
            myHandler.postDelayed(myRunnable, 2000);
        }

我用这个

import android.app.Activity;
import android.support.annotation.StringRes;
import android.widget.Toast;

public class ExitApp {

    private static long lastClickTime;

    public static void now(Activity ctx, @StringRes int message) {
        now(ctx, ctx.getString(message), 2500);
    }

    public static void now(Activity ctx, @StringRes int message, long time) {
        now(ctx, ctx.getString(message), time);
    }

    public static void now(Activity ctx, String message, long time) {
        if (ctx != null && !message.isEmpty() && time != 0) {
            if (lastClickTime + time > System.currentTimeMillis()) {
                ctx.finish();
            } else {
                Toast.makeText(ctx, message, Toast.LENGTH_SHORT).show();
                lastClickTime = System.currentTimeMillis();
            }
        }
    }

}

使用到事件onBackPressed

@Override
public void onBackPressed() {
   ExitApp.now(this,"Press again for close");
}

或ExitApp.now(这个,R.string.double_back_pressed)

对于需要关闭的更改秒，指定毫秒

ExitApp.now (R.string.double_back_pressed, 5000)

private static final int TIME_INTERVAL = 2000;
private long mBackPressed;
    @Override
        public void onBackPressed() {

            if (mBackPressed + TIME_INTERVAL > System.currentTimeMillis()) {
                super.onBackPressed();
                Intent intent = new Intent(FirstpageActivity.this,
                        HomepageActivity.class);
                startActivity(intent);
                finish();

                return;
            } else {

                Toast.makeText(getBaseContext(),
                        "Tap back button twice  to go Home.", Toast.LENGTH_SHORT)
                        .show();

                mBackPressed = System.currentTimeMillis();

            }

        }

我只是想分享一下我是如何做到的，我只是在我的活动中添加了:

private boolean doubleBackToExitPressedOnce = false;

@Override
protected void onResume() {
    super.onResume();
    // .... other stuff in my onResume ....
    this.doubleBackToExitPressedOnce = false;
}

@Override
public void onBackPressed() {
    if (doubleBackToExitPressedOnce) {
        super.onBackPressed();
        return;
    }
    this.doubleBackToExitPressedOnce = true;
    Toast.makeText(this, R.string.exit_press_back_twice_message, Toast.LENGTH_SHORT).show();
}

它就像我想要的那样工作。包括每当活动恢复时对状态的重置。

最近，我需要在我的一个应用程序中实现这个后退按钮功能。对最初问题的回答是有用的，但我必须考虑到另外两点:

在某些时间点，返回按钮被禁用 主要的活动是将片段与反向堆栈结合使用

根据回答和评论，我创建了以下代码:

private static final long BACK_PRESS_DELAY = 1000;

private boolean mBackPressCancelled = false;
private long mBackPressTimestamp;
private Toast mBackPressToast;

@Override
public void onBackPressed() {
    // Do nothing if the back button is disabled.
    if (!mBackPressCancelled) {
        // Pop fragment if the back stack is not empty.
        if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
            super.onBackPressed();
        } else {
            if (mBackPressToast != null) {
                mBackPressToast.cancel();
            }

            long currentTimestamp = System.currentTimeMillis();

            if (currentTimestamp < mBackPressTimestamp + BACK_PRESS_DELAY) {
                super.onBackPressed();
            } else {
                mBackPressTimestamp = currentTimestamp;

                mBackPressToast = Toast.makeText(this, getString(R.string.warning_exit), Toast.LENGTH_SHORT);
                mBackPressToast.show();
            }
        }
    }
}

上面的代码假设使用了支持库。如果您使用片段而不是支持库，则需要用getFragmentManager()替换getSupportFragmentManager()。

如果后退按钮从未取消，则删除第一个if。删除第二个if，如果你不使用片段或片段返回堆栈

另外，重要的是要知道onBackPressed方法从Android 2.0开始就被支持了。查看本页详细描述。为了使背按功能也适用于旧版本，将以下方法添加到您的活动中:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)  {
    if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.ECLAIR
            && keyCode == KeyEvent.KEYCODE_BACK
            && event.getRepeatCount() == 0) {
        // Take care of calling this method on earlier versions of
        // the platform where it doesn't exist.
        onBackPressed();
    }

    return super.onKeyDown(keyCode, event);
}

在这里，我已经概括编写了N个点击计数的代码。代码类似地为android设备中的启用开发人员选项编写。甚至你可以在开发人员测试应用程序时使用它来启用功能。

 private Handler tapHandler;
 private Runnable tapRunnable;
 private int mTapCount = 0;
 private int milSecDealy = 2000;

onCreate(){
 ...
tapHandler = new Handler(Looper.getMainLooper());

 }

在退按或注销选项时调用askToExit()。

private void askToExit() {
   if (mTapCount >= 2) {
    releaseTapValues();
    /* ========= Exit = TRUE  =========  */
   }

   mTapCount++;
   validateTapCount();
  }


  /* Check with null to avoid create multiple instances of the runnable */
  private void validateTapCount() {
   if (tapRunnable == null) {
    tapRunnable = new Runnable() {
     @Override
     public void run() {
      releaseTapValues();
      /* ========= Exit = FALSE  =========  */
     }
    };
    tapHandler.postDelayed(tapRunnable, milSecDealy);
   }
  }

  private void releaseTapValues() {
   /* Relase the value  */
   if (tapHandler != null) {
    tapHandler.removeCallbacks(tapRunnable);
    tapRunnable = null; /* release the object */
    mTapCount = 0; /* release the value */
   }
  }


  @Override
  protected void onDestroy() {
   super.onDestroy();
   releaseTapValues();
  }