Question

我创建了以下子类来做一些自定义绘图：

//  DocumentIconView.h

@interface DocumentIconView : UIView
{
    UIImageView     *documentIconView;
    CloseHandle     *closeHandle;
    UILabel         *filenameLabel;
}

@property (nonatomic, strong) UIImageView *documentIconView;
@property (nonatomic, strong) CloseHandle *closeHandle;
@property (nonatomic, strong) UILabel *filenameLabel;

+ (DocumentIconView *)documentIconWithFrame:(CGRect)viewFrame
                     previewImage:(UIImage *)previewImage
                            title:(NSString *)title;

这大部分都适用（我可以实例化对象，并进行自定义绘图），但是，我无法从其他类访问它的某些属性。

DocumentIconView *iconView = [DocumentIconView documentIconWithFrame:frame 
                                                      previewImage:[UIImage imageNamed:@"GenericDocumentIcon.png"] 
                                                             title:[NSString stringWithFormat:@"test"]];

iconView.backgroundColor = [UIColor lightGrayColor];  // this works
iconView.filenameLabel.backgroundColor = [UIColor darkGrayColor]; // this does not work - no error message
[documentsView addSubview:iconView];

我可以读写第一级属性，但不能深入钻取;尝试读取属性时，返回的值为(null)

我在子类化方面相当新，所以我觉得我错过了一些非常明显的东西。任何帮助将不胜感激。

编辑：实例化相关视图的方法：

+ (DocumentIconView *)documentIconWithFrame:(CGRect)viewFrame
                     previewImage:(UIImage *)previewImage
                            title:(NSString *)title
{
    DocumentIconView *view = [[DocumentIconView alloc] initWithFrame:viewFrame];

    // Close handle's size is assigned here
    CGSize closeHandleSize = CGSizeMake(27, 27);

    // The document preview image's frame is calculated by shrinking it by the close handle's size
    CGRect documentPreviewFrame = CGRectMake(closeHandleSize.width / 2, 
                                           closeHandleSize.height / 2, 
                                           viewFrame.size.width - closeHandleSize.width, 
                                             viewFrame.size.height - closeHandleSize.height - 20); // 20 points is the filenameLabel's height

    UIImageView *documentPreviewView = [[UIImageView alloc] initWithFrame:documentPreviewFrame];
    documentPreviewView.contentMode = UIViewContentModeScaleAspectFit;
    documentPreviewView.backgroundColor = [UIColor clearColor];
    documentPreviewView.image = previewImage;

    [view addSubview:documentPreviewView];

    CGRect closeHandleFrame = CGRectMake(0, 0, closeHandleSize.width, closeHandleSize.height);
    CloseHandle *closeHandleView = [[CloseHandle alloc] initWithFrame:closeHandleFrame];

    closeHandleView.alpha = 0.0;
    closeHandleView.tag = kCloseHandleTag;
    [view addSubview:closeHandleView];

    CGRect filenameFrame = CGRectMake(0, 
                                      viewFrame.size.height - 20, 
                                      viewFrame.size.width, 
                                      20);
    UILabel *filenameLabel = [[UILabel alloc] initWithFrame:filenameFrame];
    filenameLabel.backgroundColor = [UIColor clearColor];
    filenameLabel.text = title;
    filenameLabel.font = [UIFont boldSystemFontOfSize:17];
    filenameLabel.textColor = [UIColor whiteColor];
    filenameLabel.textAlignment = UITextAlignmentCenter; 
    [view addSubview:filenameLabel];

    view.tag = kDocumentIconTag;

    return view;
}

Answer 1

在documentIconWithFrame:...方法中，您使用的是您要添加到视图中的局部变量（filenameLabel）。这意味着您的实例变量从未实例化，始终为nil。

只需改变一下：

UILabel *filenameLabel = [[UILabel alloc] initWithFrame:filenameFrame];

到此：

filenameLabel = [[UILabel alloc] initWithFrame:filenameFrame];

和其他实例变量相同。

无法访问子类的属性

1 个答案: