在iOS 7中，在UIButton子类上不断调用layoutSubviews方法 [英] In iOS 7, layoutSubviews method is called constantly on UIButton subclass

问题描述

我在视图上有一个UIButton的子类。适用于iOS 6,5等。但在iOS 7中，当我尝试更改标题时，我注意到延迟（使用setTitle：forState :)。我已经将问题追溯到这样一个事实：基金会不断在我的控件上调用layoutSubviews，这导致CPU使用率在应用程序的生命周期内徘徊在100％左右。

I have a subclass of UIButton on a view. Works great in iOS 6, 5, etc. But in iOS 7, I'm noticing delays when I try to change the title (using setTitle:forState:). I've tracked down the issue to the fact that the foundation is constantly calling layoutSubviews on my control, and this causing the CPU usage to hover around 100% for the lifetime of the app.

在我的子类中，我覆盖了layoutSubviews并添加了一个断点来诊断问题。回溯仅显示从基础中的[UIView layoutSublayersOfLayer]方法调用的方法。

In my subclass, I overrode layoutSubviews and added a breakpoint to diagnose the problem. The backtrace only shows the method called from the [UIView layoutSublayersOfLayer] method in the foundation.

请注意，如果我注释掉这一行：

Note that if I comment out this line:

[super layoutSubviews];

CPU问题消失了，但当然，其他问题出现。

the CPU problem goes away, but, of course, other problems arise.

有没有人见过这个？为什么iOS 7会不断调用layoutSubviews？

Has anyone seen this? Why is iOS 7 calling layoutSubviews constantly?

推荐答案

发现问题。在我的setEnabled：方法（首先是子类的部分原因）中，我有以下几行：

Found the problem. In my setEnabled: method (part of the reason for the subclass in the first place), I had the following line:

self.titleLabel.alpha = enabled ? 1.0 : 0.8;

显然在iOS 7中，这会导致UIButton开始一个永远不会完成的标题更改动画。结果是一个无限循环，其中layoutSubviews被重复调用。

And apparently in iOS 7, this causes UIButton to begin a title-change animation that it never finishes. The result is an infinite loop in which layoutSubviews is repeatedly called.

当titleColor改变时，修复是包括这一行：

The fix was to include this line when the titleColor is changed:

[self setTitleColor:[[self titleColorForState:UIControlStateNormal] colorWithAlphaComponent:0.8] forState:UIControlStateDisabled];

避免无限循环！

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