客观C++从C访问一个NSSlider ++回调

Question

AppController.h

@interface AppController : NSObject { 

} 

@property (retain) IBOutlet NSSlider * mySlider; 

void setMySlider (NSSlider *ns);// c function 

AppController.m

@implementation AppController 

int myAmount=0; 
@synthesize mySlider; 


void setMySlider(NSSlider *mySlider){ 

    [ns setIntValue:10]; //ok 
    ns.intValue =myAmount;//ok 
} 

myCallBackFunction(double delta,std::vector<unsigned char>*myData,void *userData){ 

myAmount=50; 
NSLog(@"%i", myAmount); // ok does display value of myAmount 

// should move my slider the value of my amount by calling the following C function: 

changeSliderVelocity(mySlider);// error message mySlider was not declared in this scope 

} 

Answer 1

号

在这种情况下，即使myCallBackFunction()放置@implementation和@end之间它不在AppController的类范围内。 int myAmount就像一个静态的Class-Ish成员（我实际上不知道它的作用域是什么。Global？），因为你在Implementation文件中定义了它，它实际上并不是对象AppController的一部分。

没有保证这将工作，但给它一个镜头。它假定只有一个（一个）AppController实例。阅读关于Obj-C/C++中单例的更多信息。

@implementation AppController 

static AppController *sharedAppInstance = nil; 

- (void) init 
{ 
    // ... whatever other code you have 
    if (sharedAppInstance == nil) 

    sharedAppController = self; //error message sharedAppController was not declared in //this scope. So I replaced the line sharedAppController = self; by: 

     sharedAppInstance= self; 

} 

myCallBackFunction(double delta,std::vector<unsigned char>*myData,void *userData){ 

changeSliderVelocity([[AppController sharedAppInstance] mySlider]); // Replace this line with to make it work: 
changeSliderVelocity([sharedAppInstance mySlider]);//ok does work. 

} 

@end