ios - UIView 的值为 YES 的不透明属性是否与其值为 [UIColor clearColor] 的 backgroundColor 属性冲突？

Question

如代码:

view.opaque = YES;

和

view.backgroundColor = [UIColor clearColor];

谁能解释一下？

编辑:

如文档所示:

Declare Views as Opaque Whenever Possible

UIKit uses the opaque property of each view to determine whether the view can optimize compositing operations. Setting the value of this property to YES for a custom view tells UIKit that it does not need to render any content behind your view. Less rendering can lead to increased performance for your drawing code and is generally encouraged. Of course, if you set the opaque property to YES, your view must fills its bounds rectangle completely with fully opaque content.

不透明属性用于判断 View 是否可以优化合成操作。

所以问题是:

如果我设置view.opaque = YES和view.backgroundColor = [UIColor clearColor]，前者提高了性能，后者呢？

Answer 1

不透明标志用于渲染优化。如果在 View 不应不透明时将其设置为 YES，如果您确实希望通过 View 可以看到事物，则可能会出现意外的渲染。

我的理解是，有时会检查不透明标志以查看是否应该检查 alpha 值。