返回键退出程序的两种方式.zip
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在Android开发中,当用户按下设备的返回键时,通常会期望应用能够关闭或者返回到上一级界面。这里我们将深入探讨两种主要的方式,使应用程序在Android中响应返回键并实现退出程序的功能。 第一种方式是通过重写Activity的onBackPressed()方法。这个方法在用户点击返回键时默认被调用。我们可以在自定义的Activity类中覆盖此方法,加入退出程序的逻辑: ```java @Override public void onBackPressed() { // 提示用户是否确认退出 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { new AlertDialog.Builder(this) .setTitle("确认退出") .setMessage("确定要退出吗?") .setCancelable(false) .setPositiveButton("确定", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // 关闭所有活动并退出应用 finishAffinity(); } }) .setNegativeButton("取消", null) .show(); } else { // 旧版本的API处理方式 new AlertDialog.Builder(this) .setTitle("确认退出") .setMessage("确定要退出吗?") .setCancelable(false) .setPositiveButton("确定", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // 关闭当前Activity finish(); } }) .show(); } } ``` 上述代码首先创建了一个对话框来询问用户是否真的想要退出。如果用户在Android 3.0(HONEYCOMB)及以上版本的设备上,我们会使用finishAffinity()方法关闭所有活动,从而彻底退出应用。对于旧版本的Android,我们只需要调用finish()来关闭当前Activity即可。 第二种方式是通过监听系统的Back键事件。这需要我们在Activity中注册一个HardwareKeyListener,并在接收到返回键事件时执行退出操作: ```java @Override public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN) { if (event.getRepeatCount() == 0) { // 提示用户是否确认退出 new AlertDialog.Builder(this) .setTitle("确认退出") .setMessage("确定要退出吗?") .setCancelable(false) .setPositiveButton("确定", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // 关闭所有活动并退出应用 finishAffinity(); } }) .setNegativeButton("取消", null) .show(); return true; } } return super.onKeyDown(keyCode, event); } ``` 这种方式下,我们检查了按键事件的keyCode是否为KEYCODE_BACK,以及ACTION是否为ACTION_DOWN,这样可以确保只在用户首次按下返回键时触发对话框。同样,确认后我们使用finishAffinity()或finish()来结束应用。 这两种方法都可以有效地帮助开发者实现返回键退出程序的需求。然而,需要注意的是,通常情况下,Android鼓励提供一致的用户体验,这意味着应用不应该在没有明确提示的情况下突然退出。因此,在实际开发中,使用返回键退出应用之前,最好向用户显示一个确认对话框,以避免意外退出。
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