ios - 如果 sizeToFit 依赖于 layoutSubviews，如何实现？
<p><p>在 <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIView_Class/#//apple_ref/occ/instm/UIView/layoutSubviews" rel="noreferrer noopener nofollow">layoutSubviews</a> 的文档中，苹果说:</p>
<blockquote>
<p>You should not call this method directly.</p>
</blockquote>
<p>我正在尝试实现 <code>sizeToFit</code>。我希望它在所有 subview 上放置一个紧密的边界框。在确定这样的边界框之前，我必须布局 subview 。这意味着我必须调用 Apple 不赞成的 <code>layoutSubviews</code>。如何在不违反 Apple 规则的情况下解决这个难题？</p>
<pre><code>- (void)layoutSubviews
{
;
self.view0.frame = something;
self.view1.frame = somethingElse;
}
- (void)sizeToFit
{
;
self.frame = CGRectMake(
self.frame.origin.x,
self.frame.origin.y,
MAX(
self.view0.frame.origin.x + self.view0.frame.size.width,
self.view1.frame.origin.x + self.view1.frame.size.width
),
MAX(
self.view0.frame.origin.y + self.view0.frame.size.height,
self.view1.frame.origin.y + self.view1.frame.size.height
)
);
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>不应覆盖 <code>-sizeToFit</code>。而是用 View 的当前边界大小覆盖 <code>-sizeThatFits:</code>，它由 <code>-sizeToFit</code> 内部调用。</p>
<blockquote>
<p>You should not override this method. If you want to change the default sizing information for your view, override the sizeThatFits: instead. That method performs any needed calculations and returns them to this method, which then makes the change. – <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIView_Class/#//apple_ref/occ/instm/UIView/sizeToFit" rel="noreferrer noopener nofollow">UIView Class Reference</a></p>
</blockquote>
<hr/>
<p>同样，即使您将覆盖 <code>-sizeToFit</code>，也很可能没有理由立即执行布局。您只需调整 View 的大小，即设置其边界大小。这会触发对<code>-setNeedsLayout</code> 的调用，将 View 标记为<em>需要布局</em>。但除非您想为 View 设置动画，否则不必立即应用新布局。</p>
<p>这种延迟更新模式的要点是，如果您执行多次连续更新，它会节省大量时间，因为实际更新只执行一次。</p>
<hr/>
<p>我通常这样做。它就像一个魅力。</p>
<pre><code>#pragma mark - Layout & Sizing
- (void)layoutSubviews
{
;
}
- (CGSize)sizeThatFits:(CGSize)size
{
CGFloat const width = size.width;
CGFloat const height = ;
return CGSizeMake(width, height);
}
- (CGFloat)calculateHeightForWidth:(CGFloat)width applyLayout:(BOOL)apply
{
CGRect const topViewFrame = ({
CGRect frame = CGRectZero;
...
frame;
});
CGRect const bottomViewFrame = ({
CGRect frame = CGRectZero;
...
frame;
});
if (apply) {
self.topView.frame = topViewFrame;
self.bottomView.frame = bottomViewFrame;
}
return CGRectGetMaxY(bottomViewFrame);
}
</code></pre>
<p>请注意，示例代码适用于可以以任何宽度显示的 View ，并且容器会要求特定宽度的首选高度。</p>
<p>不过，您可以轻松地调整其他布局样式的代码。</p></p>
<p style="font-size: 20px;">关于ios - 如果 sizeToFit 依赖于 layoutSubviews，如何实现？，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/29287431/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/29287431/
</a>
</p>
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