xcode UIImageView 仅在我调用 initWithImage 时显示
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UIImageView only displays when I call initWithImage
提问by Kevin_TA
For some reason, I can only display a UIImageView when I alloc/init it each iteration with a different image. What's strange is I know the image data is being loaded because I am running processing on the image and the processing is working as expected. In short, here are the two methods I was trying:
出于某种原因，我只能在每次迭代使用不同的图像分配/初始化 UIImageView 时显示它。奇怪的是我知道正在加载图像数据，因为我正在对图像进行处理并且处理按预期工作。简而言之，这是我尝试的两种方法：
// interface
@interface ViewController : UIViewController <UIAlertViewDelegate>
{
UIImageView *imageView;
}
@property (nonatomic, retain) UIImageView *imageView;
@end
// implementation
@implementation ViewController
@synthesize imageView;
//...
- (void) loadAndDisplayImage {
// Load testing image
UIImage *testImg;
testImg = [UIImage imageNamed:@"Test.png"];
self.imageView = [[UIImageView alloc] initWithImage:testImg];
//size of imageView rect
CGRect frame = self.imageView.frame;
int ivw = frame.size.width;
int ivh = frame.size.height;
//...
}
@end
When I use this method self.imageView = [[UIImageView alloc] initWithImage:testImg];the ivwand ivhhave valid values and the image is displayed. However, if I change the implementation to this:
当我使用此方法时self.imageView = [[UIImageView alloc] initWithImage:testImg];，ivw和ivh具有有效值并显示图像。但是，如果我将实现更改为：
// implementation
@implementation ViewController
@synthesize imageView;
//...
- (void) viewDidLoad {
self.imageView = [[UIImageView alloc] init];
[self loadAndDisplayImage];
}
- (void) loadAndDisplayImage {
// Load testing image
UIImage *testImg;
testImg = [UIImage imageNamed:@"Test.png"];
self.imageView.image = testImg;
//size of imageView rect
CGRect frame = self.imageView.frame;
int ivw = frame.size.width;
int ivh = frame.size.height;
//...
}
@end
Where I am setting the image using self.imageView.image = testImg;, the values ivwand ivhare both zero and no image is displayed but the subsequent processing on the image is still accurate. In both cases, I am sending the image to processing using [self doRecognizeImage:self.imageView.image];. I can't figure out how this is possible. It would make a lot more sense to me if the processing failed when the image could not be shown.
在我使用 设置图像的地方self.imageView.image = testImg;，值ivw和ivh都为零并且不显示图像，但对图像的后续处理仍然准确。在这两种情况下，我都将图像发送到使用[self doRecognizeImage:self.imageView.image];. 我无法弄清楚这怎么可能。如果在无法显示图像时处理失败，对我来说会更有意义。
Ideas? Thanks.
想法？谢谢。
回答by occulus
The problem is that when you set the imageproperty on an already-init'd UIImageView, the frame size isn't updated to match the new image size (unlike initWithImage:).
问题在于，当您image在已经初始化的 d 上设置属性时UIImageView，帧大小不会更新以匹配新的图像大小（与 不同initWithImage:）。
Whenever you have a problem like this, it's always worth checking out the docsin case you missed something:
每当您遇到这样的问题时，总是值得查看文档以防您遗漏某些内容：
Setting the image property does not change the size of a UIImageView. Call sizeToFit to adjust the size of the view to match the image.
设置图像属性不会改变 UIImageView 的大小。调用 sizeToFit 来调整视图的大小以匹配图像。
So, add a call to sizeToFitafter you've set the image property:
因此，sizeToFit在设置图像属性后添加调用：
self.imageView.image = testImg;
[self.imageView sizeToFit];
As a side note, I'd only use the self.dot notation when you're writing to a property, not reading it, or calling a method. In other words, you can get away with just writing:
作为旁注，我只会self.在写入属性时使用点符号，而不是读取它或调用方法。换句话说，你可以只写：
// we are not setting imageView itself here, only a property on it
imageView.image = testImg;
// this is a method call, so "self." not needed
[imageView sizeToFit];
回答by Stoph
It might be possible that your image view isn't resizing for the image, so you're loading an image into a UIImageView with a frame of zero size. Try manually setting the frame of the image view to some other value. Something along the lines of:
您的图像视图可能没有为图像调整大小，因此您将图像加载到 UIImageView 中，框架大小为零。尝试手动将图像视图的框架设置为其他值。类似的东西：
UIImageView* test = [[UIImageView alloc] init];
[test setFrame:CGRectMake(0, 0, 100, 100)];
