如何通过代码更改UIImageView图像内容？

Question

I use this to assign image:

UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"myImage" ofType:@"png"]];
CGRect cropRect = CGRectMake(175, 0, 175, 175);
CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], cropRect);
imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 175, 175)];
imageView.image = [UIImage imageWithCGImage:imageRef];
[self addSubview:imageView];
CGImageRelease(imageRef);

Now, I want to change the image from myImage to myImage2, so I do that:

    UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"myImage2" ofType:@"png"]];
CGRect cropRect = CGRectMake(175, 0, 175, 175);
CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], cropRect);
imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 175, 175)];
imageView.image = [UIImage imageWithCGImage:imageRef];
[self addSubview:imageView];

It works, but not the way I want, I want to change the image, not add a imageView on top of the pervious one. How can I modify my code? thx u.

Answer 1

Alternatively, this can be done with tags.

//Set up the imageView in viewDidLoad or similar
UIImageView * imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 175, 175)];
[imageView setTag:123];
[self.view addSubview:imageView];
[imageView release];

Then any time you want to change the image, you just have to use:

[(UIImageView*)[self.view viewWithTag:123] setImage:[UIImage imageWithCGImage:imageRef]];

Just another option, the other answers will work just as well.

Answer 2

I just spent a day looking at this tricky issue, so I thought I would share how to change images on a UIImageView. Too many posts regarding this were not able to show a simple way of doing this so here goes...

If you want to change an image displayed on an imageView

In your .h

IBOutlet UIImageView *imageView;
@property (nonatomic, retain, readwrite) IBOutlet UIImageView *imgView;

and in your .m

-(void)viewDidLoad
{
    [super viewDidLoad];
    self.imageView = [[UIImageView alloc] initWithFrame:CGRectMake(133, 230, 60, 60)];
    self.imageView.image = [UIImage imageNamed:@"firstPicure.png"];
    [self.view addSubview:self.imageView];
}

Now change your image displayed in your imageView. One nice thing about this method is that imageNamed will return an autorelease instance of an image so you can avoid memory leaks and for simplicity sake you use performSelectorOnMainThread to handle the change

-(void)changeImage
{
    [self.imageView performSelectorOnMainThread:@selector(setImage:) withObject: [UIImage imageNamed:@"secondPicture.png"] waitUntilDone:YES];
}

Answer 3

I am not sure why you are bothering to crop the image; just set the contentMode property appropriately. Alternative approach:

UIImage *image = [UIImage imageNamed:@"myImage.png"];
UIImage *image2 = [UIImage imageNamed:@"myImage2.png"];
UIImageView *imageView = [[UIImageView alloc] initWithFrame:...];
imageView.contentMode = UIViewContentModeTopLeft;
imageView.image = image;
[self.view addSubView:imageView];
...
imageView.image = image2;

Answer 4

At the moment, you're creating a new UIImageView and adding it to the list of sub views. As you're seeing, you then end up with two image views. What you want is to just change the image displayed by the first view. Retain a handle to the UIImageView you create (probably as a member field), and when you want to change the image, just write

UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"myImage2" ofType:@"png"]];
imageView.image = [UIImage imageWithCGImage:imageRef];