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7. 观察者Observer模式的代码实现并使用IDemux进行测试~1

发布时间：2021-06-09 14:50:56编辑：雪饮阅读（）

 先实现观察者服务好吧。

cpp/CMakeLists.txt:
# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.10.2)

# Declares and names the project.

project("xplay")

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.
#添加頭文件路徑(括號中的include是相對於本文件路徑)
include_directories(../../../include)
#設置ffmpeg庫所在路徑的變量，這裏的FF是自定義的一個名字
set(FF ${CMAKE_CURRENT_SOURCE_DIR}/../../../libs/${ANDROID_ABI})
#avcodec這個是自定義的一個名字
add_library(avcodec SHARED IMPORTED)
set_target_properties(avcodec PROPERTIES IMPORTED_LOCATION ${FF}/libavcodec.so)

add_library(avformat SHARED IMPORTED)
set_target_properties(avformat PROPERTIES IMPORTED_LOCATION ${FF}/libavformat.so)

add_library(avutil SHARED IMPORTED)
set_target_properties(avutil PROPERTIES IMPORTED_LOCATION ${FF}/libavutil.so)

add_library(swscale SHARED IMPORTED)
set_target_properties(swscale PROPERTIES IMPORTED_LOCATION ${FF}/libswscale.so)

add_library(swresample SHARED IMPORTED)
set_target_properties(swresample PROPERTIES IMPORTED_LOCATION ${FF}/libswresample.so)
add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
            #src/main/cpp/native-lib.cpp
            IDemux
            FFDemux
            XData
            XLog
            native-lib.cpp
            XThread
            IObserver
        )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       native-lib
                       GLESv2 EGL
                       OpenSLES
                       android
                       avcodec avformat avutil swscale swresample
                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )
然后在入口native-lib.cpp中实例化一个观察者服务：

#include <jni.h>
#include <string>
#include "FFDemux.h"
#include "XLog.h"
class TestObs:public IObserver
{
public:
    void Update(XData d)
    {
        XLOGI("TestObs Update data size is %d",d.size);
    }
};
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_xplay_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    TestObs *tobs = new TestObs();
    IDemux *de = new FFDemux();
    de->AddObs(tobs);
    de->Open("/sdcard/1080.mp4");
    de->Start();
    XSleep(3000);
    de->Stop();
    return env->NewStringUTF(hello.c_str());
}

然后在观察者的应用实体中每读取一帧数据就进行通知：IDemux.cpp： #include "IDemux.h"
#include "XLog.h"

void IDemux::Main()
{
    while(!isExit)
    {

        XData d = Read();
        if(d.size > 0)
            Notify(d);
        //XLOGI("IDemux Read %d",d.size);
        //if(d.size<=0)break;
    }
}

那么实体自然要继承自观察者：IDemux.h： #ifndef XPLAY_IDEMUX_H
#define XPLAY_IDEMUX_H

#include "XData.h"
#include "XThread.h"
#include "IObserver.h"

//解封装接口
class IDemux: public IObserver {
public:
    //打开文件，或者流媒体 rmtp http rtsp
    virtual bool Open(const char *url) = 0;

    //读取一帧数据，数据由调用者清理
    virtual XData Read() = 0;

    //总时长（毫秒）
    int totalMs = 0;
protected:
    virtual void Main();

};


#endif //XPLAY_IDEMUX_H

然后是观察者服务的具体实现cpp/IObserver.cpp: #include "IObserver.h"


//主体函数添加观察者
void IObserver::AddObs(IObserver *obs)
{
    if(!obs)return;
    mux.lock();
    obss.push_back(obs);
    mux.unlock();
}

//通知所有观察者
void IObserver::Notify(XData data)
{

    mux.lock();
    for(int i =0; i < obss.size(); i++)
    {
        obss[i]->Update(data);
    }
    mux.unlock();

}

虽然这里obss.push_back可能会报红，意思是push_back在obss中不存在该函数，但是该函数是c++中的，个人认为这里没有问题，可能是因为vector导致的android studio不太识别。但是实际编译运行是没有问题的。

然后观察者和主体的声明于cpp/IObserver.h:
#ifndef XPLAY_IOBSERVER_H
#define XPLAY_IOBSERVER_H

#include "XData.h"
#include "XThread.h"
#include <vector>
#include <mutex>

//观察者和主体
class IObserver:public XThread
{
public:
    //观察者接收数据函数
    virtual void Update(XData data) {}

    //主体函数添加观察者(线程安全)
    void AddObs(IObserver *obs);

    //通知所有观察者(线程安全)
    void Notify(XData data);

protected:
    std::vector<IObserver *>obss;
    std::mutex mux;
};


#endif //XPLAY_IOBSERVER_H

最后编译运行如在魅族16T中是没有问题的。