iphone - 设置 UILabel 背景颜色会导致应用崩溃

Question

我有以下代码：

UIImageView *photo = [[[UIImageView alloc] initWithFrame:CGRectMake(title_bar.titleView.frame.origin.x+130, title_bar.titleView.frame.origin.y-12, 22.0, 22.0)] autorelease];
UIImage *theImage = [UIImage imageNamed:@"question mark icon"];
photo.image = theImage;
UIView *new_view = [[UIView alloc] init];
[new_view addSubview:photo];
UILabel *new_label = [[UILabel alloc] initWithFrame:CGRectMake(title_bar.titleView.frame.origin.x-145, title_bar.titleView.frame.origin.y-12, 268.0, 22.0)];
[new_label setText:@"gregrgtg"];
[new_label setBackgroundColor:[UIColor clearColor]]; //COMMENTING THIS LINE OUT MAKES IT WORK
[new_view addSubview:new_label];
title_bar.titleView = new_view;

当背景颜色设置为清除时，程序 SIGABRTs。如果我注释掉那行，它工作正常（除了标签的背景只是白色）。另外，如果我只是初始化标签而不是 initWithFrame-ing 它，程序不会崩溃，但我的标签看不到。

Answer 1

UIImageView *photo = [[[UIImageView alloc] initWithFrame:CGRectMake(title_bar.titleView.frame.origin.x+130, title_bar.titleView.frame.origin.y-12, 22.0, 22.0)] autorelease];
UIImage *theImage = [UIImage imageNamed:@"question mark icon"];
photo.image = theImage;
UIView *new_view = [[UIView alloc] init];
[new_view addSubview:photo];

title_bar.titleView = new_view;//this line by madhu

UILabel *new_label = [[UILabel alloc] initWithFrame:CGRectMake(title_bar.titleView.frame.origin.x-145, title_bar.titleView.frame.origin.y-12, 268.0, 22.0)];
[new_label setText:@"gregrgtg"];
[new_label setBackgroundColor:[UIColor clearColor]]; //COMMENTING THIS LINE OUT MAKES IT WORK
[new_view addSubview:new_label];

原因 ：

你已经添加了你的标题栏的标题视图，但之前提到了它们。