客觀C++從C訪問一個NSSlider ++回調

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

號

在這種情況下，即使myCallBackFunction()放置@implementation和@end之間它不在AppController的類範圍內。 int myAmount就像一個靜態的Class-Ish成員（我實際上不知道它的作用域是什麼。Global？），因爲你在Implementation文件中定義了它，它實際上並不是對象AppController的一部分。

沒有保證這將工作，但給它一個鏡頭。它假定只有一個（一個）AppController實例。閱讀關於Obj-C/C++中單例的更多信息。

@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