Android部分手机通知权限关闭无法打出Toast

0.现象描述

比如华为，三星，魅族等一些手机，如果关闭某个应用的通知权限，然后应用类的toast就无法打出来了，表示很无解，难道要自己做一个view给用户提示吗？答案是当然不需要，还可以拯救一下。。。

1.导致无法弹出toast的原因

为了查一下原因，我们先去看看源码，下图是Toast的show方法

    /**
     * Show the view for the specified duration.
     */
    public void show() {
        if (mNextView == null) {
            throw new RuntimeException("setView must have been called");
        }
        INotificationManager service = getService();
        String pkg = mContext.getOpPackageName();
        TN tn = mTN;
        tn.mNextView = mNextView;
        try {
            service.enqueueToast(pkg, tn, mDuration);
        } catch (RemoteException e) {
            // Empty
        }
    }

Toast中的show()方法，show方法中调用 service.enqueueToast(pkg, tn, mDuration); 那么service是什么呢？下面看看getService()的方法。

 static private INotificationManager getService() {
        if (sService != null) {
            return sService;
        }
        sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));
        return sService;
    }

INotificationManager 是跨进程通信的 Binder 类，sService 是 NMS(NotificationManagerService) 在客户端的代理，发送通知要委托给 sService，由它传递给 NMS，这里获取了远程的一个服务，用来调用远程的enqueueToast方法。
接下来看看NotificationManagerService.java中的enqueueToast方法，源码如下：

public void enqueueToast(String pkg, ITransientNotification callback, int duration)
        {
            if (DBG) {
                Slog.i(TAG, "enqueueToast pkg=" + pkg + " callback=" + callback + " duration=" + duration);
            }
            if (pkg == null || callback == null) {
                Slog.e(TAG, "Not doing toast. pkg=" + pkg + " callback=" + callback);
                return ;
            }
            final boolean isSystemToast = isCallerSystem() || ("android".equals(pkg));
            final boolean isPackageSuspended = isPackageSuspendedForUser(pkg, Binder.getCallingUid());

            if (ENABLE_BLOCKED_TOASTS && (!noteNotificationOp(pkg, Binder.getCallingUid())
                    || isPackageSuspended)) {

                if (!isSystemToast) {
                    Slog.e(TAG, "Suppressing toast from package " + pkg
                            + (isPackageSuspended? " due to package suspended by administrator."  : " by user request."));
                    return;
                }
            }
            synchronized (mToastQueue) {
                int callingPid = Binder.getCallingPid();
                long callingId = Binder.clearCallingIdentity();
                try {
                    ToastRecord record;
                    int index = indexOfToastLocked(pkg, callback);
                    // If it's already in the queue, we update it in place, we don't
                    // move it to the end of the queue.
                    if (index >= 0) {
                        record = mToastQueue.get(index);
                        record.update(duration);
                    } else {
                        // Limit the number of toasts that any given package except the android
                        // package can enqueue.  Prevents DOS attacks and deals with leaks.
                        if (!isSystemToast) {
                            int count = 0;
                            final int N = mToastQueue.size();
                            for (int i=0; i<N; i++) {
                                final ToastRecord r = mToastQueue.get(i);
                                if (r.pkg.equals(pkg)) {
                                    count++;
                                    if (count >= MAX_PACKAGE_NOTIFICATIONS) {
                                        Slog.e(TAG, "Package has already posted " + count
                                                + " toasts. Not showing more. Package=" + pkg);
                                        return;
                                    }
                                }
                            }
                        }
                        record = new ToastRecord(callingPid, pkg, callback, duration);
                        mToastQueue.add(record);
                        index = mToastQueue.size() - 1;
                        keepProcessAliveLocked(callingPid);
                    }

                    // If it's at index 0, it's the current toast.  It doesn't matter if it's
                    // new or just been updated.  Call back and tell it to show itself.
                    // If the callback fails, this will remove it from the list, so don't
                    // assume that it's valid after this.

                    if (index == 0) {
                        showNextToastLocked();
                    }
                } finally {
                    Binder.restoreCallingIdentity(callingId);
                }
            }
        }

从以上代码可知，如果noteNotificationOp()方法返回了false，也就是这个包名的通知权限被禁用，那么就会return，致使无法弹出Toast！

2.怎么解决

参考网络上的一些解决方案, 如下方案是把pkg名字改成“android”，这样就不用管权限了。

/**
     * 显示系统Toast
     */
    private static void showSystemToast(Toast toast){
        try{
            Method getServiceMethod = Toast.class.getDeclaredMethod("getService");
            getServiceMethod.setAccessible(true);

            final Object iNotificationManager = getServiceMethod.invoke(null);
            Class iNotificationManagerCls = Class.forName("android.app.INotificationManager");
            Object iNotificationManagerProxy = Proxy.newProxyInstance(toast.getClass().getClassLoader(), new Class[]{iNotificationManagerCls}, new InvocationHandler() {
                @Override
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                    // 强制使用系统Toast
                    // 华为p20 pro上为enqueueToastEx
                    if("enqueueToast".equals(method.getName())
                            || "enqueueToastEx".equals(method.getName())){
                        args[0] = "android";
                    }
                    return method.invoke(iNotificationManager, args);
                }
            });
            Field sServiceFiled = Toast.class.getDeclaredField("sService");
            sServiceFiled.setAccessible(true);
            sServiceFiled.set(null, iNotificationManagerProxy);
            toast.show();

        }catch (Exception e){
            e.printStackTrace();
        }
    }