上一节中，我们最终调用了Application的run方法。
在run方法中，调用了applicationDidFinishLaunching方法，这个方法在哪里呢？
可以看到在Application中并没有实现这个方法，这个方法来自Application的基类ApplicationProtocol。
ApplicationProtocol中，将applicationDidFinishLaunching声明为纯虚函数，最终的实现放到了AppDelegate中。
//AppDelegate.h
#ifndef __APP_DELEGATE__
#define __APP_DELEGATE__
#include "Application.h"
#include <iostream>
class AppDelegate: private Application {
public:
virtual bool applicationDidFinishLaunching() {
std::cout << "delegate applicationDidFinishLaunching" << std::endl;
return true;
}
};
#endif
添加了对纯虚函数applicationDidFinishLaunching的实现，在其中打印了一句话。
// Application.h
#ifndef __APPLICATION__
#define __APPLICATION__
#include "ApplicationProtocol.h"
#include <iostream>
class Application: public ApplicationProtocol {
public:
Application() {
sm_pSharedApplication = this;
}
static Application* getInstance() {
return sm_pSharedApplication;
}
int run() {
std::cout << "App run ..." << std::endl;
if (!applicationDidFinishLaunching()) {
return 1;
}
}
protected:
static Application * sm_pSharedApplication;
};
Application * Application::sm_pSharedApplication = 0;
#endif
在Application中添加了对applicationDidFinishLaunching的调用，并让他继承自抽象类ApplicationProtocol。
//ApplicationProtocol.h
class ApplicationProtocol {
public:
virtual ~ApplicationProtocol(){}
virtual bool applicationDidFinishLaunching() = 0;
}; 在这个抽象类中声明纯虚函数applicationDidFinishLaunching。
编译运行可以看到最终输出：
App run ...
delegate applicationDidFinishLaunching
附代码：demo2
