Android7.0 MessageQueue

Posted

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了Android7.0 MessageQueue相关的知识,希望对你有一定的参考价值。

android中的消息处理机制大量依赖于Handler。每个Handler都有对应的Looper,用于不断地从对应的MessageQueue中取出消息处理。
一直以来,觉得MessageQueue应该是Java层的抽象,然而事实上MessageQueue的主要部分在Native层中。
自己对MessageQueue在Native层的工作不太熟悉,借此机会分析一下。

一、MessageQueue的创建
当需要使用Looper时,我们会调用Looper的prepare函数:

public static void prepare() {
    prepare(true);
}

private static void prepare(boolean quitAllowed) {
    if (sThreadLocal.get() != null) {
        throw new RuntimeException("Only one Looper may be created per thread");
    }
    //sThreadLocal为线程本地存储区;每个线程仅有一个Looper
    sThreadLocal.set(new Looper(quitAllowed));
}

private Looper(boolean quitAllowed) {
    //创建出MessageQueue
    mQueue = new MessageQueue(quitAllowed);
    mThread = Thread.currentThread();
}

1 NativeMessageQueue
我们看看MessageQueue的构造函数:

MessageQueue(boolean quitAllowed) {
    mQuitAllowed = quitAllowed;
    //mPtr的类型为long?
    mPtr = nativeInit();
}

MessageQueue的构造函数中就调用了native函数,我们看看android_os_MessageQueue.cpp中的实现:

static jlong android_os_MessageQueue_nativeInit(JNIEnv* env, jclass clazz) {
    //MessageQueue的Native层实体
    NativeMessageQueue* nativeMessageQueue = new NativeMessageQueue();
    ............
    //这里应该类似与将指针转化成long类型,放在Java层保存;估计Java层使用时,会在native层将long变成指针,就可以操作队列了
    return reinterpret_cast<jlong>(nativeMessageQueue);
}

我们跟进NativeMessageQueue的构造函数:

NativeMessageQueue::NativeMessageQueue() :
        mPollEnv(NULL), mPollObj(NULL), mExceptionObj(NULL) {
    //创建一个Native层的Looper,也是线程唯一的
    mLooper = Looper::getForThread();
    if (mLooper == NULL) {
        mLooper = new Looper(false);
        Looper::setForThread(mLooper);
    }
}

从代码来看,Native层和Java层均有Looper对象,应该都是操作MessageQueue的。MessageQueue在Java层和Native层有各自的存储结构,分别存储Java层和Native层的消息。

2 Native层的looper

我们看看Native层looper的构造函数:

Looper::Looper(bool allowNonCallbacks) :
        mAllowNonCallbacks(allowNonCallbacks), mSendingMessage(false),
        mPolling(false), mEpollFd(-1), mEpollRebuildRequired(false),
        mNextRequestSeq(0), mResponseIndex(0), mNextMessageUptime(LLONG_MAX) {
    //此处创建了个fd
    mWakeEventFd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
    .......
    rebuildEpollLocked();
}

在native层中,MessageQueue中的Looper初始化时,还调用了rebuildEpollLocked函数,我们跟进一下:

void Looper::rebuildEpollLocked() {
    // Close old epoll instance if we have one.
    if (mEpollFd >= 0) {
        close(mEpollFd);
    }

    // Allocate the new epoll instance and register the wake pipe.
    mEpollFd = epoll_create(EPOLL_SIZE_HINT);
    ............
    struct epoll_event eventItem;
    memset(& eventItem, 0, sizeof(epoll_event)); // zero out unused members of data field union
    eventItem.events = EPOLLIN;
    eventItem.data.fd = mWakeEventFd;
    //在mEpollFd上监听mWakeEventFd上是否有数据到来
    int result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeEventFd, & eventItem);
    ...........
    for (size_t i = 0; i < mRequests.size(); i++) {
        const Request& request = mRequests.valueAt(i);
        struct epoll_event eventItem;
        request.initEventItem(&eventItem);
        //监听request对应fd上数据的到来
        int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, request.fd, & eventItem);
        ............
    }
}

从native层的looper来看,我们知道Native层依赖于epoll来驱动事件处理。此处我们先保留一下大致的映像,后文详细分析。

二、使用MessageQueue
1 写入消息
Android中既可以在Java层向MessageQueue写入消息,也可以在Native层向MessageQueue写入消息。我们分别看一下对应的操作流程。

1.1 Java层写入消息
Java层向MessageQueue写入消息,依赖于enqueueMessage函数:

boolean enqueueMessage(Message msg, long when) {
    if (msg.target == null) {
        throw new IllegalArgumentException("Message must have a target.");
    }
    if (msg.isInUse()) {
        throw new IllegalStateException(msg + " This message is already in use.");
    }

    synchronized (this) {
        if (mQuitting) {
            .....
            return false;
        }

        msg.markInUse();
        msg.when = when;
        Message p = mMessages;
        boolean needWake;
        if (p == null || when == 0 || when < p.when) {
            // New head, wake up the event queue if blocked.
            msg.next = p;
            mMessages = msg;
            //在头部插入数据,如果之前MessageQueue是阻塞的,那么现在需要唤醒
            needWake = mBlocked;
        } else {
            // Inserted within the middle of the queue.  Usually we don‘t have to wake
            // up the event queue unless there is a barrier at the head of the queue
            // and the message is the earliest asynchronous message in the queue.
            needWake = mBlocked && p.target == null && msg.isAsynchronous();
            Message prev;
            for (;;) {
                prev = p;
                p = p.next;
                if (p == null || when < p.when) {
                    break;
                }
                //不是第一个异步消息时,needWake置为false
                if (needWake && p.isAsynchronous()) {
                    needWake = false;
                }
            }
            msg.next = p; // invariant: p == prev.next
            prev.next = msg;
        }
        // We can assume mPtr != 0 because mQuitting is false.
        if (needWake) {
            nativeWake(mPtr);
        }
    }
    return true;
}

上述代码比较简单,主要就是将新加入的Message按执行时间插入到原有的队列中,然后根据情况调用nativeAwake函数。

我们跟进一下nativeAwake:

void NativeMessageQueue::wake() {
    mLooper->wake();
}

void Looper::wake() {
    uint64_t inc = 1;
    //就是向mWakeEventFd写入数据
    ssize_t nWrite = TEMP_FAILURE_RETRY(write(mWakeEventFd, &inc, sizeof(uint64_t)));
    .............
}

在native层的looper初始化时,我们提到过native层的looper将利用epoll来驱动事件,其中构造出的epoll句柄就监听了mWakeEventFd。
实际上从MessageQueue中取出数据时,若没有数据到来,就会利用epoll进行等待;因此当Java层写入消息时,将会将唤醒处于等待状态的MessageQueue。
在后文介绍从MessageQueue中提取消息时,将再次分析这个问题。

1.2 Native层写入消息
Native层写入消息,依赖于Native层looper的sendMessage函数:

void Looper::sendMessage(const sp<MessageHandler>& handler, const Message& message) {
    nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
    sendMessageAtTime(now, handler, message);
}

void Looper::sendMessageAtTime(nsecs_t uptime, const sp<MessageHandler>& handler,
        const Message& message) {
    size_t i = 0;
    {
        AutoMutex _l(mLock);

        //同样需要按时间插入
        size_t messageCount = mMessageEnvelopes.size();
        while (i < messageCount && uptime >= mMessageEnvelopes.itemAt(i).uptime) {
            i += 1;
        }

        //将message包装成一个MessageEnvelope对象
        MessageEnvelope messageEnvelope(uptime, handler, message);
        mMessageEnvelopes.insertAt(messageEnvelope, i, 1);

        // Optimization: If the Looper is currently sending a message, then we can skip
        // the call to wake() because the next thing the Looper will do after processing
        // messages is to decide when the next wakeup time should be.  In fact, it does
        // not even matter whether this code is running on the Looper thread.
        if (mSendingMessage) {
            return;
        }
    }
    // Wake the poll loop only when we enqueue a new message at the head.
    if (i == 0) {
        //若插入在队列头部,同样利用wake函数触发epoll唤醒
        wake();
    }
}

以上就是向MessageQueue中加入消息的主要流程,接下来我们看看从MessageQueue中取出消息的流程。

2、提取消息
当Java层的Looper对象调用loop函数时,就开始使用MessageQueue提取消息了:

public static void loop() {
    final Looper me = myLooper();
    .......
    for (;;) {
        Message msg = queue.next(); // might block
        .......
        try {
            //调用Message的处理函数进行处理
            msg.target.dispatchMessage(msg);
        }........
    }
}

此处我们看看MessageQueue的next函数:

Message next() {
    //mPtr保存了NativeMessageQueue的指针
    final long ptr = mPtr;
    .......
    int pendingIdleHandlerCount = -1; // -1 only during first iteration
    int nextPollTimeoutMillis = 0;

    for (;;) {
        if (nextPollTimeoutMillis != 0) {
            //会调用Native函数,最终调用IPCThread的talkWithDriver,将数据写入Binder驱动或者读取一次数据
            //不知道在此处进行这个操作的理由?
            Binder.flushPendingCommands();
        }

        //处理native层的数据,此处会利用epoll进行blocked
        nativePollOnce(ptr, nextPollTimeoutMillis);

        synchronized (this) {
            final long now = SystemClock.uptimeMillis();
            Message prevMsg = null;
            Message msg = mMessages;
            //下面其实就是找出下一个异步处理类型的消息;异步处理类型的消息,才含有对应的执行函数
            if (msg != null && msg.target == null) {
                // Stalled by a barrier.  Find the next asynchronous message in the queue.
                do {
                    prevMsg = msg;
                    msg = msg.next;
                } while (msg != null && !msg.isAsynchronous());
            }

            if (msg != null) {
                if (now < msg.when) {
                    // Next message is not ready.  Set a timeout to wake up when it is ready.
                    nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);
                } else {
                    // Got a message.
                    mBlocked = false;
                    //完成next记录的存储
                    if (prevMsg != null) {
                        prevMsg.next = msg.next;
                    } else {
                        mMessages = msg.next;
                    }
                    msg.next = null;
                    if (DEBUG) Log.v(TAG, "Returning message: " + msg);
                    msg.markInUse();
                    return msg;
                }
            } else {
                // No more messages.
                nextPollTimeoutMillis = -1;
            }

            // Process the quit message now that all pending messages have been handled.
            if (mQuitting) {
                dispose();
                return null;
            }

            //MessageQueue中引入了IdleHandler接口,即当MessageQueue没有数据处理时,调用IdleHandler进行一些工作

            //pendingIdleHandlerCount表示待处理的IdleHandler,初始为-1
            if (pendingIdleHandlerCount < 0
                    && (mMessages == null || now < mMessages.when)) {
                //mIdleHandlers的size默认为0,调用接口addIdleHandler才能增加
                pendingIdleHandlerCount = mIdleHandlers.size();
            }

            if (pendingIdleHandlerCount <= 0) {
                // No idle handlers to run.  Loop and wait some more.
                mBlocked = true;
                continue;
            }

            //将待处理的IdleHandler加入到PendingIdleHandlers中
            if (mPendingIdleHandlers == null) {
                mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
            }
            //调用ArrayList.toArray(T[])节省每次分配的开销;毕竟对于Message.Next这样调用频率较高的函数,能省一点就是一点
            mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
        }

        for (int i = 0; i < pendingIdleHandlerCount; i++) {
            final IdleHandler idler = mPendingIdleHandlers[i];
            mPendingIdleHandlers[i] = null; // release the reference to the handler

            boolean keep = false;
            try {
                //执行实现类的queueIdle函数,返回值决定是否继续保留
                keep = idler.queueIdle();
            } catch (Throwable t) {
                Log.wtf(TAG, "IdleHandler threw exception", t);
            }

            if (!keep) {
                synchronized (this) {
                    mIdleHandlers.remove(idler);
                }
            }
        }
        pendingIdleHandlerCount = 0;
        nextPollTimeoutMillis = 0;
    }
}

技术分享

整个提取消息的过程,大致上如上图所示。
可以看到在Java层,Looper除了要取出MessageQueue的消息外,还会在队列空闲期执行IdleHandler定义的函数。

2.1 nativePollOnce
现在唯一的疑点是nativePollOnce是如何处理Native层数据的,我们看看对应的native函数:

static void android_os_MessageQueue_nativePollOnce(JNIEnv* env, jobject obj,
        jlong ptr, jint timeoutMillis) {
    //果然Java层调用native层MessageQueue时,将long类型的ptr变为指针
    NativeMessageQueue* nativeMessageQueue = reinterpret_cast<NativeMessageQueue*>(ptr);
    nativeMessageQueue->pollOnce(env, obj, timeoutMillis);
}

void NativeMessageQueue::pollOnce(JNIEnv* env, jobject pollObj, int timeoutMillis) {
    mPollEnv = env;
    mPollObj = pollObj;
    //最后还是进入到Native层looper的pollOnce函数
    mLooper->pollOnce(timeoutMillis);
    mPollObj = NULL;
    mPollEnv = NULL;

    if (mExceptionObj) {
        .........
    }
}

看看native层looper的pollOnce函数:

//timeoutMillis为超时等待时间。值为-1时,表示无限等待直到有事件到来;值为0时,表示无需等待
//outFd此时为null,含义是:存储产生事件的文件句柄
//outEvents此时为null,含义是:存储outFd上发生了哪些事件,包括可读、可写、错误和中断
//outData此时为null,含义是:存储上下文数据,其实调用时传入的参数
int Looper::pollOnce(int timeoutMillis, int* outFd, int* outEvents, void** outData) {
    int result = 0;
    for (;;) {
        //处理response,目前我们先不关注response的内含
        while (mResponseIndex < mResponses.size()) {
            const Response& response = mResponses.itemAt(mResponseIndex++);
            int ident = response.request.ident;
            if (ident >= 0) {
                int fd = response.request.fd;
                int events = response.events;
                void* data = response.request.data;

                if (outFd != NULL) *outFd = fd;
                if (outEvents != NULL) *outEvents = events;
                if (outData != NULL) *outData = data;
                return ident;
            }
        }

        //根据pollInner的结果,进行操作
        if (result != 0) {
            if (outFd != NULL) *outFd = 0;
            if (outEvents != NULL) *outEvents = 0;
            if (outData != NULL) *outData = NULL;
            return result;
        }

        //主力还是靠pollInner
        result = pollInner(timeoutMillis);
    }
}

跟进一下pollInner函数:

int Looper::pollInner(int timeoutMillis) {
    // Adjust the timeout based on when the next message is due.
    //timeoutMillis是Java层事件等待事件
    //native层维持了native message的等待时间
    //此处其实就是选择最小的等待时间
    if (timeoutMillis != 0 && mNextMessageUptime != LLONG_MAX) {
         nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
         int messageTimeoutMillis = toMillisecondTimeoutDelay(now, mNextMessageUptime);
         if (messageTimeoutMillis >= 0
                && (timeoutMillis < 0 || messageTimeoutMillis < timeoutMillis)) {
            timeoutMillis = messageTimeoutMillis;
        }
    }

    int result = POLL_WAKE;
    //pollInner初始就清空response
    mResponses.clear();
    mResponseIndex = 0;

    // We are about to idle.
    mPolling = true;

    //利用epoll等待mEpollFd监控的句柄上事件到达
    struct epoll_event eventItems[EPOLL_MAX_EVENTS];
    int eventCount = epoll_wait(mEpollFd, eventItems, EPOLL_MAX_EVENTS, timeoutMillis);

    // No longer idling.
    mPolling = false;

    // Acquire lock.
    mLock.lock();

    //重新调用rebuildEpollLocked时,将使得epoll句柄能够监听新加入request对应的fd
    if (mEpollRebuildRequired) {
        mEpollRebuildRequired = false;
        rebuildEpollLocked();
        goto Done;
    }

    // Check for poll error.
    if (eventCount < 0) {
        if (errno == EINTR) {
            goto Done;
        }
        ......
        result = POLL_ERROR;
        goto Done;
    }

    // Check for poll timeout.
    if (eventCount == 0) {
        result = POLL_TIMEOUT;
        goto Done;
    }

    for (int i = 0; i < eventCount; i++) {
        if (fd == mWakeEventFd) {
            if (epollEvents & EPOLLIN) {
                //前面已经分析过,当java层或native层有数据写入队列时,将写mWakeEventFd,以触发epoll唤醒
                //awoken将读取并清空mWakeEventFd上的数据
                awoken();
            } else {
                .........
            }
        } else {
            //epoll同样监听的request对应的fd
            ssize_t requestIndex = mRequests.indexOfKey(fd);
            if (requestIndex >= 0) {
                int events = 0;
                if (epollEvents & EPOLLIN) events |= EVENT_INPUT;
                if (epollEvents & EPOLLOUT) events |= EVENT_OUTPUT;
                if (epollEvents & EPOLLERR) events |= EVENT_ERROR;
                if (epollEvents & EPOLLHUP) events |= EVENT_HANGUP;
                //存储这个fd对应的response
                pushResponse(events, mRequests.valueAt(requestIndex));
            } else {
                ..........
            }
        }
    }

Done:
    // Invoke pending message callbacks.
    mNextMessageUptime = LLONG_MAX;
    //处理Native层的Message
    while (mMessageEnvelopes.size() != 0) {
        nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
        const MessageEnvelope& messageEnvelope = mMessageEnvelopes.itemAt(0);
        if (messageEnvelope.uptime <= now) {
            // Remove the envelope from the list.
            // We keep a strong reference to the handler until the call to handleMessage
            // finishes.  Then we drop it so that the handler can be deleted *before*
            // we reacquire our lock.
            {
                sp<MessageHandler> handler = messageEnvelope.handler;
                Message message = messageEnvelope.message;
                mMessageEnvelopes.removeAt(0);
                mSendingMessage = true;
                mLock.unlock();

                //处理Native Message
                handler->handleMessage(message);
            }
            mLock.lock();
            mSendingMessage = false;
            result = POLL_CALLBACK;
        } else {
            // The last message left at the head of the queue determines the next wakeup time.
            mNextMessageUptime = messageEnvelope.uptime;
            break;
        }
    }

    // Release lock.
    mLock.unlock();

    //处理带回调函数的response
    for (size_t i = 0; i < mResponses.size(); i++) {
        Response& response = mResponses.editItemAt(i);
        if (response.request.ident == POLL_CALLBACK) {
            int fd = response.request.fd;
            int events = response.events;
            void* data = response.request.data;

            //调用response的callback
            int callbackResult = response.request.callback->handleEvent(fd, events, data);
            if (callbackResult == 0) {
                removeFd(fd, response.request.seq);
            }

            response.request.callback.clear();
            result = POLL_CALLBACK;
        }
    }
    return result;
}

技术分享

说实话native层的代码写的很乱,该函数的功能比较多。
如上图所示,在nativePollOnce中利用epoll监听是否有数据到来,然后处理native message、native response。

最后,我们看看如何在native层中加入request。

3 添加监控请求
native层增加request依赖于looper的接口addFd:

//fd表示需要监听的句柄
//ident的含义还没有搞明白
//events表示需要监听的事件,例如EVENT_INPUT、EVENT_OUTPUT、EVENT_ERROR和EVENT_HANGUP中的一个或多个
//callback为事件发生后的回调函数
//data为回调函数对应的参数
int Looper::addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data) {
    return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : NULL, data);
}

结合上文native层轮询队列的操作,我们大致可以知道:addFd的目的,就是让native层的looper监控新加入的fd上是否有指定事件发生。
如果发生了指定的事件,就利用回调函数及参数构造对应的response。
native层的looper处理response时,就可以执行对应的回调函数了。

看看实际的代码:

int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {
    ........
    {
        AutoMutex _l(mLock);

        //利用参数构造一个request
        Request request;
        request.fd = fd;
        request.ident = ident;
        request.events = events;
        request.seq = mNextRequestSeq++;
        request.callback = callback;
        request.data = data;
        if (mNextRequestSeq == -1) mNextRequestSeq = 0; // reserve sequence number -1

        struct epoll_event eventItem;
        request.initEventItem(&eventItem);

        //判断之前是否已经利用该fd构造过Request
        ssize_t requestIndex = mRequests.indexOfKey(fd);
        if (requestIndex < 0) {
            //mEpollFd新增一个需监听fd
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
            .......
            mRequests.add(fd, request);
        } else {
            //mEpollFd修改旧的fd对应的监听事件
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_MOD, fd, & eventItem);
            if (epollResult < 0) {
                if (errno == ENOENT) {
                    // Tolerate ENOENT because it means that an older file descriptor was
                    // closed before its callback was unregistered and meanwhile a new
                    // file descriptor with the same number has been created and is now
                    // being registered for the first time. 
                    epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
                    .......
                }
                //发生错误重新加入时,安排EpollRebuildLocked,将让epollFd重新添加一次待监听的fd
                scheduleEpollRebuildLocked();
            }
            mRequests.replaceValueAt(requestIndex, request);
        }
    }
}

对加入监控请求的处理,在上文介绍pollInner函数时已做分析,此处不再赘述。

三、总结

1、流程总结
技术分享

MessageQueue的整个流程包括了Java部分和Native部分,从图中可以看出Native层的比重还是很大的。我们结合上图回忆一下整个MessageQueue对应的处理流程:
1、Java层创建Looper对象时,将会创建Java层的MessageQueue;Java层的MessageQueue初始化时,将利用Native函数创建出Native层的MessageQueue。

2、Native层的MessageQueue初始化后,将创建对应的Native Looper对象。Native对象初始化时,将创建对应epollFd和WakeEventFd。其中,epollFd将作为epoll的监听句柄,初始时epollFd仅监听WakeEventFd。

3、图中红色线条为Looper从MessageQueue中取消息时,处理逻辑的流向。
3.1、当Java层的Looper开始循环时,首先需要通过JNI函数调用Native Looper进行pollOnce的操作。

3.2、Native Looper开始运行后,需要等待epollFd被唤醒。当epollFd等待超时或监听的句柄有事件到来,Native Looper就可以开始处理事件了。

3.3、在Native层,Native Looper将先处理Native MessageQueue中的消息,再调用Response对应的回调函数。

3.4、本次循环中,Native层事件处理完毕后,才开始处理Java层中MessageQueue的消息。若MessageQueue中没有消息需要处理,并且MessageQueue中存在IdleHandler时,将调用IdleHandler定义的处理函数。

图中蓝色部分为对应的函数调用:
在Java层:
利用MessageQueue的addIdleHandler,可以为MessageQueue增加IdleHandler;
利用MessageQueue的enqueueMessage,可以向MessageQueue增加消息;必要时将利用Native函数向Native层的WakeEventFd写入消息,以唤醒epollFd。

在Native层:
利用looper:sendMessage,可以为Native MessageQueue增加消息;同样,要时将向Native层的WakeEventFd写入消息,以唤醒epollFd;
利用looper:addFd,可以向Native Looper注册监听请求,监听请求包含需监听的fd、监听的事件及对应的回调函数等,监听请求对应的fd将被成为epollFd监听的对象。当被监听的fd发生对应的事件后,将会唤醒epollFd,此时将生成对应response加入的response List中,等待处理。一旦response被处理,就会调用对应的回调函数。

2、注意事项
MessageQueue在Java层和Native层有各自的存储结构,可以分别增加消息。从处理逻辑来看,会优先处理native层的Message,然后处理Native层生成的response,最后才是处理Java层的Message。



























以上是关于Android7.0 MessageQueue的主要内容,如果未能解决你的问题,请参考以下文章

Android7.0打开sdacrd图片问题

Android7.0新特性,及Android N适配

Android7.0多窗口实现原理

Android7.0新特性,及Android N适配

Android7.0新特性,及Android N适配

Android 升级安装APK兼容Android7.0,解决FileUriExposedException