IOS setNeedsDisplay 和 setNeedsLayout

最新推荐文章于 2019-03-05 18:21:11 发布

最新推荐文章于 2019-03-05 18:21:11 发布 · 124 阅读

本文深入探讨iOS开发中视图管理的关键方法：setNeedsDisplay、drawRect、setNeedsLayout、layoutSubviews等，详细解释了它们的作用及用法，并提供实际应用场景，帮助开发者高效完成界面布局与渲染。

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setNeedsDisplay：

Marks the receiver’s entire bounds rectangle as needing to be redrawn.

drawRect:

This method is called when a view is first displayed or when an event occurs that invalidates a visible part of the view. You should never call this method directly yourself. To invalidate part of your view, and thus cause that portion to be redrawn, call the setNeedsDisplay orsetNeedsDisplayInRect: method instead.

setNeedsLayout：

Invalidates the current layout of the receiver and triggers a layout update during the next update cycle.

layoutIfNeeded

Use this method to force the layout of subviews before drawing.Lays out the subviews immediately.

layoutSubviews：

You should not call this method directly. If you want to force a layout update, call thesetNeedsLayout method instead to do so prior to the next drawing update. If you want to update the layout of your views immediately, call thelayoutIfNeeded method.

总之你要是排布子视图就在layoutSubviews：

你要是画一些东西就在drawRect: