UIImageView仅在我调用initWithImage时显示 [英] UIImageView only displays when I call initWithImage

问题描述

出于某种原因，我只能在每次迭代时使用不同的图像分配/初始化时显示UIImageView。奇怪的是我知道正在加载图像数据，因为我正在对图像运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：

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:

// 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

当我使用此方法 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：

When I use this method self.imageView = [[UIImageView alloc] initWithImage:testImg]; the ivw and ivh have valid values and the image is displayed. However, if I change the implementation to this:

// 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

我使用 self.imageView.image = testImg; 设置图像，值 ivw 和 ivh 均为零且未显示图像，但对图像的后续处理仍然准确。在这两种情况下，我都使用 [self doRecognizeImage：self.imageView.image]; 将图像发送到处理中。我无法弄清楚这是怎么可能的。如果在无法显示图像时处理失败，对我来说会更有意义。

Where I am setting the image using self.imageView.image = testImg;, the values ivw and ivh are 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.

想法？谢谢。

推荐答案

问题是当你设置图像属性时已初始化 UIImageView ，帧大小未更新以匹配新图像大小（与 initWithImage：不同） ）。

The problem is that when you set the image property on an already-init'd UIImageView, the frame size isn't updated to match the new image size (unlike initWithImage:).

每当遇到这样的问题时，总是值得查看 docs ，以防错过：

Whenever you have a problem like this, it's always worth checking out the docs in case you missed something:

设置image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。

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.

因此，添加对<$ c的调用$ c> sizeToFit 设置图像属性后：

So, add a call to sizeToFit after you've set the image property:

self.imageView.image = testImg;
[self.imageView sizeToFit];

作为附注，我只使用 self。当您写入属性，不读取或调用方法时，点符号。换句话说，你只需写一下就可以了：

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:

// 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];     

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