在CGRectZero中使用autoResizingMask [英] Using autoResizingMask with CGRectZero

问题描述

我正在为tableview的部分建立页脚.页脚的高度将在heightForFooterInSection中指定，因此在viewForFooterInSection中，我只想添加子视图并指定页脚视图应填充指定的任何页脚高度(此页脚大小将是动态的).因此，我将CGRectZero用作初始框架，并告诉页脚视图展开以填充其父视图.

I am building a footer for a tableview's section. The height of the footer will be specified in heightForFooterInSection, so in viewForFooterInSection I would like to just add the subview and specify that the footer view should fill whatever footer height is specified (this footer size will be dynamic). So, I am using CGRectZero as the initial frame and telling the footer view to expand to fill its parent view.

- (UIView *)tableView:(UITableView *)tableView viewForFooterInSection:(NSInteger)section
{
    UIView *footerView = [[UIView alloc] initWithFrame:CGRectZero];
    footerView = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    footerView = [UIColor greenColor];
    return footerView;
}

这可以按预期工作-表格视图的页脚完全用绿色视图填充.

This works as expected - the footer of the table view is filled completely with the green view.

但是现在我想在页脚中添加UITextView.文本视图应填充相同的空间，但保留5点边框:

But now I want to add a UITextView to the footer. The text view should fill the same space, but leave a 5-point border:

{
    UIView *footerView = [[UIView alloc] initWithFrame:CGRectZero];
    footerView = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    footerView = [UIColor greenColor];

    UITextView *textView = [[UITextView alloc] initWithFrame:CGRectInset(footerView.frame, 5, 5)];
    textView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    textView.backgroundColor = [UIColor redColor];

    [footerView addSubview:textView];
    return footerView;
}

不是填充页脚视图(具有5磅的边距)，而是完全不显示文本视图.它可能具有CGRectZero的帧(甚至可能是-5 x -5?).但是，如果将插图设置为0、0，则它会按预期扩展.

Instead of filling the footer view (with a 5 point margin), the text view does not appear at all. It likely has a frame of CGRectZero (or maybe even -5 x -5?). If I set the inset to 0, 0, however, it expands as expected.

对此有何解释?并且如果我不能在初始帧中使用CGRectZero的插图，那么当footerView的帧未知时，我应该使用什么?

What is the explanation for this? And If I can't use an inset of CGRectZero for the initial frame, what am I expected to use when the frame of the footerView can not be known?

推荐答案

CGRectInset将基于现有矩形创建一个矩形.它不再引用页脚视图:仅当它正在计算一次时.在这种情况下，由于您要插入大小为零的矩形，因此适用于文档:

CGRectInset will create a rectangle based on the existing rectangle. It doesn't refer to the footer view ever again: only when it is calculating it this one time. In this case, since you are trying to inset a rectangle with a zero size, this applies from the docs:

讨论. 矩形已标准化，然后插入参数为 应用.如果所得矩形的高度为负，或 宽度，则返回一个空矩形.

Discussion. The rectangle is standardized and then the inset parameters are applied. If the resulting rectangle would have a negative height or width, a null rectangle is returned.

因此，您正在使用一个空矩形创建标签.

Therefore, you are creating your label with a null rectangle.

我将创建典型"尺寸的页脚，然后使用所需的autoResizingMask创建适当尺寸的标签，然后然后将footerView设置为零(如果您希望将其设置为零)

I would create the footer with a "typical" size, then an appropriately sized label with the autoResizingMask that you want, and then set your footerView to zero if that is what you want it set to.

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