ios - UIImageview 不显示图像

Question

这是我用来显示 PGM 格式图像的代码，它早些时候可以工作，如果我将它作为一个单独的项目使用它也可以工作，但现在不工作，我无法弄清楚为什么它不工作。有人请帮助我。

- (void)viewDidLoad
{
[super viewDidLoad];

UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
CGPoint center = self.view.center;
activityIndicator.frame= CGRectMake(center.x, center.y, 37, 37);
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(center.x-30, center.y+40, 160, 30)];
[label setText:@"Calculating..."];
[self.view addSubview:activityIndicator];
[self.view addSubview:label];
[activityIndicator startAnimating];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
/////////////// read file ///////////
    FILE *file = fopen("/Users/Sumit/Desktop/test/out.pgm", "rb");
    if (file == NULL) {
        NSLog(@"File Not Found");
        return;
    }
    char name[20], secondline[10];
    int w=0, h=0, colors=0;
    fscanf(file, "%s", name);
    fscanf(file, "%s", secondline);
    fscanf(file, "%d %d %d", &w, &h, &colors);
    //printf("%d %d\n", w, h);
    unsigned char * imagedata = (unsigned char *) malloc(sizeof(unsigned char)*w*h);
    fseek(file, 1, SEEK_CUR);
    int i=0;
    while (!feof(file)) {
        int val = getc(file);
        imagedata[i] = val;
        i++;
    }
    fclose(file);
    ////////////////// end read file /////////////

    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceGray();
    CFDataRef rgbData = CFDataCreate(NULL, imagedata, w * h);
    CGDataProviderRef provider = CGDataProviderCreateWithCFData(rgbData);
    CGImageRef rgbImageRef = CGImageCreate(w, h, 8, 8, w , colorspace, kCGBitmapByteOrderDefault, provider, NULL, true, kCGRenderingIntentDefault);
    CFRelease(rgbData);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorspace);
    UIImageView *imageview = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, w, h)];
    UIImage * newimage = [UIImage imageWithCGImage:rgbImageRef];
    //imageview.frame = CGRectMake(imageview.frame.origin.x,imageview.frame.origin.y, w, h);
    [imageview setImage:newimage];
    [activityIndicator removeFromSuperview];
    [label removeFromSuperview];

    CGSize boundsSize = scrollview.bounds.size;
    CGRect frameToCenter = imageview.frame;

    // center horizontally
    if (frameToCenter.size.width < boundsSize.width)
        frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
    else
        frameToCenter.origin.x = 0;

    // center vertically
    if (frameToCenter.size.height < boundsSize.height)
        frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
    else
        frameToCenter.origin.y = 0;

    imageview.frame = frameToCenter;
    [scrollview addSubview:imageview];
    CGImageRelease(rgbImageRef);
    dispatch_async(dispatch_get_main_queue(), ^(void){
        //[alertView dismissWithClickedButtonIndex:0 animated:YES];
    });
});

// Do any additional setup after loading the view.
}

Answer 1

您必须在主线程上执行每个 UI 修改。您在另一个线程上设置图像 view.image。这是你的问题。

dispatch_async(dispatch_get_main_queue(), ^{
    imageview.image = newimage;
});

您的实际代码会影响，您的图像不会在 [imageview setImage:newimage] 之后立即设置；线，因为它在后台线程上。它会在稍后设置。