UIView性能:不透明，backgroundColor，clearsContextBeforeDrawing?

问题描述

我正在用白色背景色的超级视图中显示带有UIImageView的不透明PNG.最好的性能是什么?

I'm displaying opaque PNGs with UIImageViews inside of a superview with a white background color. What's best for performance?

opaque = NO，backgroundColor = nil，clearsContextBeforeDrawing = YES.

1. UIView类参考:backgroundColor 说，"[nil]产生透明的背景色.如果我设置 UIView的opaque属性设置为YES，我是否还必须将其backgroundColor设置为[UIColor clearColor]，还是这是多余的代码行&处理不必要吗?即[UIColor clearColor]是否被认为是不透明的(不透明)?

1. UIView Class Reference: backgroundColor says, "[nil] results in a transparent background color." If I set a UIViews opaque property to YES, must I also set its backgroundColor to [UIColor clearColor], or is that extra line of code & processing unnecessary? I.e., is [UIColor clearColor] considered opaque (not transparent)?

clearsContextBeforeDrawing的值对不透明视图有影响吗?

Does the value of clearsContextBeforeDrawing matter for opaque views?

在UIView.h中对clearsContextBeforeDrawing的注释说，对于不透明的视图，它将被忽略.

The comments for clearsContextBeforeDrawing in UIView.h say it's ignored for opaque views.

但是， UIView类参考:clearsContextBeforeDrawing 说:

是哪个?

类似问题

• 是值为YES的UIView的opaque属性与其值为[UIColor clearColor]的backgroundColor属性冲突?
• Cocoa/iPhone:BackgroundColor和不透明属性

Similar Questions

• Is UIView's opaque property with a value of YES in conflict with its backgroundColor property with a value of [UIColor clearColor]?
• Cocoa/iPhone: BackgroundColor and Opaque Properties

推荐答案

假定您的PNG始终填充整个UIImageView，则应使用以下方法获得最佳性能:

Assuming that your PNGs always fills the entire UIImageView, you should get the best performance using:

opaque = YES，clearsContextBeforeDrawing = NO.在此模式下，backgroundColor无关紧要.像素只需替换为新的图像数据即可.

opaque = YES, clearsContextBeforeDrawing = NO. In this mode backgroundColor is irrelevant. The pixels are simply replaced with the new image data.

对于单色背景上的透明PNG，最快的是:

For transparent PNGs on a single-color background, the fastest will be:

opaque = YES，clearsContextBeforeDrawing = YES和backgroundColor匹配您需要的任何内容.在这种情况下[UIColor whiteColor].

opaque = YES, clearsContextBeforeDrawing = YES, and backgroundColor matching whatever you need. In this case [UIColor whiteColor].

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