iphone - iOS 指针问题

Question

我似乎有一个指针问题，而且我似乎无法修复它。有人可以帮帮我吗？

-(void) connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"Finished Downloading Image: %@" ,[connection.originalRequest.URL absoluteString]);
    UIImage *CompiledImage=[UIImage imageWithData:ImageData];
    SEL selector=@selector(ImageDownloadingCompleted:Image:);
    if([[self Delegate] respondsToSelector:selector]){
        [[self Delegate] ImageDownloadingCompleted:self Image:CompiledImage];
    }
    else{
        if(Target){
            *Target=CompiledImage;
        }
    }
    // NSLog(@"Image Size:%i", [ImageData length]);
}

Target 是 UIImage 类型的私有(private)变量(声明:UIImage *Target;) CompiledImage 也是一个 UIImage。我要做的是将目标地址的内容设置为 CompiledTarget 的内容。这会导致以下错误:

Assigning to 'UIImage' from incompatible type 'UIImage *__strong'

我试过了:

memccpy(__bridge Target, &CompiledImage, sizeof(Target),sizeof(Target));

我得到这个错误:

Expected expression

Answer 1

你只需要将它设置为，

Target = CompiledImage;

不需要*。由于两者都是指针，如果您使用上述代码，基本上您是在分配内存地址而不是复制内容。

附带说明，请以小写字母开头变量名。 Target 通常表示一个类名。根据 Apple 编码约定，它应该是 target。

根据您的意见，您可以执行以下操作，

在ViewController类中，声明一个UIImage为@property，

@property (nonatomic, retain) UIImage *downloadedImage;

在进行 URL 调用时，

NSImageLoader *imageLoader = [[NSImageLoader alloc] init];
[imageLoader setTarget:self];//setting current viewController as target instead of UIImage

下载图片时，

-(void) connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"Finished Downloading Image: %@" ,[connection.originalRequest.URL absoluteString]);
    UIImage *CompiledImage=[UIImage imageWithData:ImageData];
    SEL selector=@selector(ImageDownloadingCompleted:Image:);
    if([[self Delegate] respondsToSelector:selector]){
        [[self Delegate] ImageDownloadingCompleted:self Image:CompiledImage];
    }
    else{
        if(Target){
            Target.downloadedImage = CompiledImage;//or [Target setDownloadedImage:CompiledImage];
        }
    }
    // NSLog(@"Image Size:%i", [ImageData length]);
}

在您的 ViewController 类中，现在您可以通过 self.downloadedImage 访问图像，它与 CompiledImage 中的相同，具有指向相同位置的相同内存地址。

另一种方法是在 NSImageLoader 类中将 UIImage *Target 声明为 UIImage **Target。在调用 setTarget 方法时，使用 [imageLoader setTarget:&Target];。在此方法中，您需要将目标设置为 Target = Target;

更新: 根据您的意见，它应该是这样的，

for( NSDictionary *CurrentActivity in [Profile UserActivities]) {
        ...
        UIImage *WineImage = [UIImage imageNamed:@"loader.gif"];
        NSImageLoader *loader=[[NSImageLoader alloc] initWithURLString:[NSString stringWithFormat:@"%@%@",[TempSettings URL],[CurrentActivity objectForKey:@"ImageURL"]]];
        [loader setTarget:&WineImage];
        [loader startDownloading];
        [self addSubview:Activity];
        Counter++;
    }

然后在NSImageLoader.h文件中@interface,

 __strong UIImage **Target; //This should be strong not autoreleasing

在 NSImageLoader.m 文件中，

- (void)setTarget:(UIImage *__strong *)iTarget{ //change here also
     Target = target; 
} 


-(void) connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"Finished Downloading Image: %@" ,[connection.originalRequest.URL absoluteString]);
    UIImage *CompiledImage=[UIImage imageWithData:ImageData];
    SEL selector=@selector(ImageDownloadingCompleted:Image:);
    if([[self Delegate] respondsToSelector:selector]){
        [[self Delegate] ImageDownloadingCompleted:self Image:CompiledImage];
    }
    else{
        if(Target){
            *Target = CompiledImage;
        }
    }
    // NSLog(@"Image Size:%i", [ImageData length]);
}

更新2:

使用传递 UIImageView 的方法，您可以执行以下操作，

    for( NSDictionary *CurrentActivity in [Profile UserActivities]) {
        ...
        UIImage *WineImage = [UIImage imageNamed:@"loader.gif"];
        NSImageLoader *loader=[[NSImageLoader alloc] initWithURLString:[NSString stringWithFormat:@"%@%@",[TempSettings URL],[CurrentActivity objectForKey:@"ImageURL"]]];
        [loader setTarget:Activity];//pass imageview and let the delegate method set image
        [loader startDownloading];
        [self addSubview:Activity];
        Counter++;
    }

-(void) connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"Finished Downloading Image: %@" ,[connection.originalRequest.URL absoluteString]);
    UIImage *CompiledImage=[UIImage imageWithData:ImageData];
    SEL selector=@selector(ImageDownloadingCompleted:Image:);
    if([[self Delegate] respondsToSelector:selector]){
        [[self Delegate] ImageDownloadingCompleted:self Image:CompiledImage];
    }
    else{
        if(Target){
            Target.image = CompiledImage;
        }
    }
    // NSLog(@"Image Size:%i", [ImageData length]);
}

此处传递 imageview 并让委托(delegate)方法在您下载图像后在其中设置图像。