iphone - 为什么我尝试在背景上显示图像会导致显示白色？

Question

我的背景来自 Default-568h@2x.png。我想在部分背景上显示缩小的 PNG，但调用:

[[CJSHCardView alloc] initWithScale:.1];

将显示屏变为白色。如果我评论这一行，这不会发生，但在函数调用中，即使我让它立即返回，它也会在半秒后将显示屏变为白色:

- (id)initWithScale:(float)scale
{
    UIImage *img = [UIImage imageNamed:@"note.png"];
    self = [super initWithImage:img];
    if (self != nil)
    {
        self.frame = CGRectMake(0, 0, img.size.width * scale, img.size.height * scale);
        UIImageView *myImage = [[UIImageView alloc] initWithFrame:self.frame];
        myImage.opaque = NO;
        [self addSubview:myImage];
    }
    return self;
}

将 return 语句移动/复制到 initWithScale 中的第一个与最后的 return 语句相比没有明显的变化:背景的简要 View ，然后是白色屏幕。 note.png 在“支持文件”中。

您是否看到我可以更改内容以显示缩小版本的笔记(保持纵横比)的任何陷阱？ note.jpg 图像没有白色像素。

谢谢，

--编辑--

关于第一条评论:

@implementation CJSHCardView : UIImageView

- (id)initWithFrame:(CGRect)frame
{
    NSAssert(NO, @"Call initWithHeight instead.");
    return self;
}

这是否回答了您的问题？

--第二次编辑--

尼克，感谢您的回复和代码。我稍微改变了它以适应 ARC 并最初设置了一个固定宽度的比例，但我有点不确定将它放入什么方法。我尝试了 ViewController 的 viewDidLoad() 方法，但这导致背景显示没有隐藏或发的说明。我现在的 viewDidLoad() 方法是这样写的:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIImage *backgroundImage = [UIImage imageNamed:@"Default-568h"];
    CGRect containerRect = CGRectZero;
    containerRect.size = [backgroundImage size];
    UIView *containerView = [[UIView alloc] initWithFrame:containerRect];
    float scale=.1;

    UIImageView *backgroundView = [[UIImageView alloc] initWithImage:backgroundImage];
    [containerView addSubview:backgroundView];
    [backgroundView sizeToFit];
    // [backgroundView release];

    UIImage *noteImage = [UIImage imageNamed:@"note"];
    CGSize noteSize = [noteImage size];
    UIImageView *noteView = [[UIImageView alloc] initWithImage:noteImage];
    [noteView setContentMode:UIViewContentModeScaleAspectFit];
    [noteView setFrame:CGRectMake(0, 0, noteSize.width * scale, noteSize.height * scale)];
    [containerView addSubview:noteView];
    // [noteView release];
}

谢谢，

Answer 1

子类化 UIImageView 不是必需的。只需创建一个容器 UIView 并添加 2 个 UIImageView subview 。

编辑 - 这应该适用于您的实现:

- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.

    UIImage *backgroundImage = [UIImage imageNamed:@"Default-568h"];
    CGRect containerRect = CGRectZero;
    containerRect.size = [backgroundImage size];
    UIView *containerView = [[UIView alloc] initWithFrame:containerRect];
    [[self view] addSubview:containerView];

    float scale=.1;

    UIImageView *backgroundView = [[UIImageView alloc] initWithImage:backgroundImage];
    [containerView addSubview:backgroundView];
    [backgroundView sizeToFit];

    UIImage *noteImage = [UIImage imageNamed:@"note"];
    CGSize noteSize = [noteImage size];
    UIImageView *noteView = [[UIImageView alloc] initWithImage:noteImage];
    [noteView setContentMode:UIViewContentModeScaleAspectFit];
    [noteView setFrame:CGRectMake(0, 0, noteSize.width * scale, noteSize.height * scale)];
    [containerView addSubview:noteView];
}