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说下什么情况下会触发布局的自动更新，怎么手动更新布局 #131

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tbfungeek opened this issue Feb 19, 2020 · 0 comments
Open

说下什么情况下会触发布局的自动更新，怎么手动更新布局 #131

tbfungeek opened this issue Feb 19, 2020 · 0 comments

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@tbfungeek
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tbfungeek commented Feb 19, 2020 •
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和约束一样，布局分为自动更新布局和手动更新布局，自动更新布局会在如下场景下发生：

1、init初始化不会触发layoutSubviews，但是用initWithFrame进行初始化的时候，当rect的值不是CGRectZero时也会触发
2、addSubview会触发layoutSubviews。
3、设置view的frame会触发layoutSubviews，当然前提是frame的值设置前后发生了变化。
4、改变一个UIView大小的时候也会触发父UIView上的layoutSubviews事件。
5、滚动一个UIScrollView会触发layoutSubviews。
6、旋转屏幕会触发父UIView上的layoutSubviews事件。

如果我们需要手动更新布局可以调用：

- (void)setNeedsLayout;

这样会在RunLoop进入休眠之前更新布局，如果想要立刻生效，可以调用：

- (void)layoutIfNeeded;

当更新布局的时候

- (void)layoutSubviews;

方法将会被触发。
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