按键2次返回

public void click(View view){
    if (isBackActivated) {
        this.finish();
    }
    if (!isBackActivated) {
        isBackActivated = true;
        Toast.makeText(getApplicationContext(), "Again", Toast.LENGTH_SHORT).show();
        Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                isBackActivated = false;  // setting isBackActivated after 2 second
            }
        }, 2000);
    }

}

我认为这是你需要的，我的意思是，当我们想要显示这个吐司时，当堆栈中只有一个活动时用户从堆栈的最后一个活动中返回。

var exitOpened=false // Declare it globaly

在onBackPressed方法中修改如下:

override fun onBackPressed() {
        if (isTaskRoot && !exitOpened)
        {
            exitOpened=true
            toast("Please press back again to exit")
            return
        }
        super.onBackPressed()
    }

在这里，如果当前活动是堆栈的根活动(第一个活动)，isTaskRoot将返回true，如果不是，则返回false。

你可以在这里查看官方文件

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。

我已经尝试为此创建了一个utils类，因此任何活动或片段都可以实现这一点，从而变得更简单。

代码是用Kotlin编写的，并且具有java互操作。

我使用协程来延迟和重置标志变量。但是您可以根据自己的需要进行修改。

其他文件:SafeToast.kt

lateinit var toast: Toast

fun Context.safeToast(msg: String, length: Int = Toast.LENGTH_LONG, action: (Context) -> Toast = default) {
    toast = SafeToast.makeText(this@safeToast, msg, length).apply {
        // do anything new here
        action(this@safeToast)
        show()
    }
}

fun Context.toastSpammable(msg: String) {
    cancel()
    safeToast(msg, Toast.LENGTH_SHORT)
}

fun Fragment.toastSpammable(msg: String) {
    cancel()
    requireContext().safeToast(msg, Toast.LENGTH_SHORT)
}

private val default: (Context) -> Toast = { it -> SafeToast.makeText(it, "", Toast.LENGTH_LONG) }

private fun cancel() {
    if (::toast.isInitialized) toast.cancel()
}

ActivityUtils.kt

@file:JvmMultifileClass
@file:JvmName("ActivityUtils")
package your.company.com

import android.app.Activity
import your.company.com.R
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch


private var backButtonPressedTwice = false

fun Activity.onBackPressedTwiceFinish() {
    onBackPressedTwiceFinish(getString(R.string.msg_back_pressed_to_exit), 2000)
}

fun Activity.onBackPressedTwiceFinish(@StringRes message: Int, time: Long) {
    onBackPressedTwiceFinish(getString(message), time)
}

fun Activity.onBackPressedTwiceFinish(message: String, time: Long) {
    if (backButtonPressedTwice) {
        onBackPressed()
    } else {
        backButtonPressedTwice = true
        toastSpammable(message)
        GlobalScope.launch {
            delay(time)
            backButtonPressedTwice = false
        }
    }
}

Kotlin中的用法

// ActivityA.kt
override fun onBackPressed() {
    onBackPressedTwiceFinish()
}

在Java中使用

@Override 
public void onBackPressed() {
    ActivityUtils.onBackPressedTwiceFinish()
}

这段代码的灵感来自这里的@webserveis

工艺流程图:

Java代码:

private long lastPressedTime;
private static final int PERIOD = 2000;

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
        switch (event.getAction()) {
        case KeyEvent.ACTION_DOWN:
            if (event.getDownTime() - lastPressedTime < PERIOD) {
                finish();
            } else {
                Toast.makeText(getApplicationContext(), "Press again to exit.",
                        Toast.LENGTH_SHORT).show();
                lastPressedTime = event.getEventTime();
            }
            return true;
        }
    }
    return false;
}

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();
  }