最近我在许多Android应用和游戏中注意到这种模式:当点击后退按钮“退出”应用时，Toast会出现类似于“请再次点击后退退出”的消息。
我在想，当我越来越频繁地看到它时，这是一个内置的功能，你可以在某个活动中访问它吗?我已经看了很多类的源代码，但我似乎找不到任何关于这一点。
当然，我可以想到一些很容易实现相同功能的方法(最简单的可能是在活动中保留一个布尔值，指示用户是否已经单击过一次…)，但我想知道这里是否已经有一些东西。
编辑:正如@LAS_VEGAS所提到的，我并不是指传统意义上的“退出”。(即终止)我的意思是“回到应用程序启动活动启动之前打开的任何东西”，如果这有意义的话:)
当前回答
对于具有导航抽屉的活动，使用下面的OnBackPressed()代码
boolean doubleBackToExitPressedOnce = false;
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
if (doubleBackToExitPressedOnce) {
if (getFragmentManager().getBackStackEntryCount() ==0) {
finishAffinity();
System.exit(0);
} else {
getFragmentManager().popBackStackImmediate();
}
return;
}
if (getFragmentManager().getBackStackEntryCount() ==0) {
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);
} else {
getFragmentManager().popBackStackImmediate();
}
}
}
其他回答
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)
你可以使用小吃店而不是吐司，所以你可以依靠它们的可见性来决定是否关闭应用程序。举个例子:
Snackbar mSnackbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final LinearLayout layout = findViewById(R.id.layout_main);
mSnackbar = Snackbar.make(layout, R.string.press_back_again, Snackbar.LENGTH_SHORT);
}
@Override
public void onBackPressed() {
if (mSnackbar.isShown()) {
super.onBackPressed();
} else {
mSnackbar.show();
}
}
根据正确的答案和评论中的建议，我创建了一个演示，工作绝对很好，并在使用后删除处理程序回调。
MainActivity.java
package com.mehuljoisar.d_pressbacktwicetoexit;
import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.widget.Toast;
public class MainActivity extends Activity {
private static final long delay = 2000L;
private boolean mRecentlyBackPressed = false;
private Handler mExitHandler = new Handler();
private Runnable mExitRunnable = new Runnable() {
@Override
public void run() {
mRecentlyBackPressed=false;
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public void onBackPressed() {
//You may also add condition if (doubleBackToExitPressedOnce || fragmentManager.getBackStackEntryCount() != 0) // in case of Fragment-based add
if (mRecentlyBackPressed) {
mExitHandler.removeCallbacks(mExitRunnable);
mExitHandler = null;
super.onBackPressed();
}
else
{
mRecentlyBackPressed = true;
Toast.makeText(this, "press again to exit", Toast.LENGTH_SHORT).show();
mExitHandler.postDelayed(mExitRunnable, delay);
}
}
}
希望对大家有所帮助!!
下面是完整的工作代码。并且不要忘记删除回调，这样它就不会在应用程序中导致内存泄漏:)
private boolean backPressedOnce = false;
private Handler statusUpdateHandler;
private Runnable statusUpdateRunnable;
public void onBackPressed() {
if (backPressedOnce) {
finish();
}
backPressedOnce = true;
final Toast toast = Toast.makeText(this, "Press again to exit", Toast.LENGTH_SHORT);
toast.show();
statusUpdateRunnable = new Runnable() {
@Override
public void run() {
backPressedOnce = false;
toast.cancel(); //Removes the toast after the exit.
}
};
statusUpdateHandler.postDelayed(statusUpdateRunnable, 2000);
}
@Override
protected void onDestroy() {
super.onDestroy();
if (statusUpdateHandler != null) {
statusUpdateHandler.removeCallbacks(statusUpdateRunnable);
}
}
你也可以使用Toast的可见性，所以你不需要Handler/postDelayed超解决方案。
Toast doubleBackButtonToast;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
doubleBackButtonToast = Toast.makeText(this, "Double tap back to exit.", Toast.LENGTH_SHORT);
}
@Override
public void onBackPressed() {
if (doubleBackButtonToast.getView().isShown()) {
super.onBackPressed();
}
doubleBackButtonToast.show();
}
