objective-c - 关于 View 层次结构，需要澄清

Question

在此代码示例中，我试图生成以下 View 层次结构

Window -> background image -> scroll view -> text view

不过我看到的是

Window -> background image

请问我错过了什么？

-(void) viewWillAppear:(BOOL)animated {

    UIScrollView *scrollWindow = [[UIScrollView alloc] 
                 initWithFrame:CGRectMake(30, 30, 440, 212)];

    UITextView *scrollableText = [[UITextView alloc] init];

    [scrollableText setEditable:NO];
    [scrollableText setText:@"Why, hello there"];

    [scrollWindow addSubview:scrollableText];

    UIImage *backgroundImage = [[UIImage alloc] initWithCGImage:
             [UIImage imageNamed:@"about_bg.png"].CGImage];
    UIImageView *backgroundView = [[UIImageView alloc] 
             initWithImage:backgroundImage];

    [backgroundView addSubview:scrollWindow];

    [[self view] addSubview:backgroundView];

}

Answer 1

Andrew 关于不让 ScrollView 成为背景 UIImageView View 的 subview 是正确的。但是 ScrollView 是不可见的。只有它的内容 (scrollableText) 会显示。而且您还没有设置 scrollableText 的框架，所以它实际上也是不可见的。像这样初始化:

[scrollableText setEditable:NO];
[scrollableText setText:@"Why, hello there"];
[scrollableText setFrame:CGRectMake(0, 0, 100, 100)];

你应该会看到它。