UIView框架，边界和中心 [英] UIView frame, bounds and center

问题描述

我想知道如何以正确的方式使用这些属性。

据我所知， frame 可以从我正在创建的视图的容器中使用。
它设置相对于容器视图的视图位置。它还设置了该视图的大小。

还可以从视图的容器中使用 center 创造。此属性更改视图相对于其容器的位置。

最后， bounds 相对于视图本身。它会更改视图的可绘制区域。

您能否提供有关 frame 之间关系的更多信息和界限？那么 clipsToBounds 和 masksToBounds 属性呢？

解决方案

由于我问过的问题多次出现，我会详细解答。如果你想添加更多正确的内容，请随意修改它。

首先回顾一下问题：框架，边界和中心及其关系。

框架视图的框架（ CGRect ）是矩形在 superview 的坐标系中的位置。默认情况下，它从左上角开始。

Bounds 视图的界限（ CGRect ）在自己的坐标系中表示一个视图矩形。

中心 A center 是以 superview 的坐标表示的 CGPoint 系统，它确定视图的确切中心点的位置。

取自

UIView框架和边界

关于 clipsToBounds （来源） Apple doc）

将此值设置为YES会导致子视图被剪切到接收器的边界
。如果设置为NO，则不会剪切其帧超出接收器的
可见边界的子视图。默认值为
NO。

换句话说，如果视图的框架是（0,0,100,100），其子视图是（90,90,30,30），您将只看到该子视图的一部分。后者不会超过父视图的界限。

masksToBounds 相当于 clipsToBounds 。而不是 UIView ，此属性应用于 CALayer 。引擎盖下， clipsToBounds 调用 masksToBounds 。如需进一步参考，请参阅如何关联UIView的clipsToBounds和CALayer的maskToBounds？。

I would like to know how to use these properties in the right manner.

As I understand, frame can be used from the container of the view I am creating. It sets the view position relative to the container view. It also sets the size of that view.

Also center can be used from the container of the view I'm creating. This property changes the position of the view relative to its container.

Finally, bounds is relative to the view itself. It changes the drawable area for the view.

Can you give more info about the relationship between frame and bounds? What about the clipsToBounds and masksToBounds properties?

解决方案

Since the question I asked has been seen many times I will provide a detailed answer of it. Feel free to modify it if you want to add more correct content.

First a recap on the question: frame, bounds and center and theirs relationships.

Frame A view's frame (CGRect) is the position of its rectangle in the superview's coordinate system. By default it starts at the top left.

Bounds A view's bounds (CGRect) expresses a view rectangle in its own coordinate system.

Center A center is a CGPoint expressed in terms of the superview's coordinate system and it determines the position of the exact center point of the view.

Taken from UIView + position these are the relationships (they don't work in code since they are informal equations) among the previous properties:

• frame.origin = center - (bounds.size / 2.0)

• center = frame.origin + (bounds.size / 2.0)

• frame.size = bounds.size

NOTE: These relationships do not apply if views are rotated. For further info, I will suggest you take a look at the following image taken from The Kitchen Drawer based on Stanford CS193p course. Credits goes to @Rhubarb.

Using the frame allows you to reposition and/or resize a view within its superview. Usually can be used from a superview, for example, when you create a specific subview. For example:

// view1 will be positioned at x = 30, y = 20 starting the top left corner of [self view]
// [self view] could be the view managed by a UIViewController
UIView* view1 = [[UIView alloc] initWithFrame:CGRectMake(30.0f, 20.0f, 400.0f, 400.0f)];    
view1.backgroundColor = [UIColor redColor];

[[self view] addSubview:view1];

When you need the coordinates to drawing inside a view you usually refer to bounds. A typical example could be to draw within a view a subview as an inset of the first. Drawing the subview requires to know the bounds of the superview. For example:

UIView* view1 = [[UIView alloc] initWithFrame:CGRectMake(50.0f, 50.0f, 400.0f, 400.0f)];    
view1.backgroundColor = [UIColor redColor];

UIView* view2 = [[UIView alloc] initWithFrame:CGRectInset(view1.bounds, 20.0f, 20.0f)];    
view2.backgroundColor = [UIColor yellowColor];

[view1 addSubview:view2];

Different behaviours happen when you change the bounds of a view. For example, if you change the bounds size, the frame changes (and vice versa). The change happens around the center of the view. Use the code below and see what happens:

NSLog(@"Old Frame %@", NSStringFromCGRect(view2.frame));
NSLog(@"Old Center %@", NSStringFromCGPoint(view2.center));    

CGRect frame = view2.bounds;
frame.size.height += 20.0f;
frame.size.width += 20.0f;
view2.bounds = frame;

NSLog(@"New Frame %@", NSStringFromCGRect(view2.frame));
NSLog(@"New Center %@", NSStringFromCGPoint(view2.center));

Furthermore, if you change bounds origin you change the origin of its internal coordinate system. By default the origin is at (0.0, 0.0) (top left corner). For example, if you change the origin for view1 you can see (comment the previous code if you want) that now the top left corner for view2 touches the view1 one. The motivation is quite simple. You say to view1 that its top left corner now is at the position (20.0, 20.0) but since view2's frame origin starts from (20.0, 20.0), they will coincide.

CGRect frame = view1.bounds;
frame.origin.x += 20.0f;
frame.origin.y += 20.0f;
view1.bounds = frame; 

The origin represents the view's position within its superview but describes the position of the bounds center.

Finally, bounds and origin are not related concepts. Both allow to derive the frame of a view (See previous equations).

View1's case study

Here is what happens when using the following snippet.

UIView* view1 = [[UIView alloc] initWithFrame:CGRectMake(30.0f, 20.0f, 400.0f, 400.0f)];
view1.backgroundColor = [UIColor redColor];

[[self view] addSubview:view1];

NSLog(@"view1's frame is: %@", NSStringFromCGRect([view1 frame]));
NSLog(@"view1's bounds is: %@", NSStringFromCGRect([view1 bounds]));
NSLog(@"view1's center is: %@", NSStringFromCGPoint([view1 center]));

The relative image.

This instead what happens if I change [self view] bounds like the following.

// previous code here...
CGRect rect = [[self view] bounds];
rect.origin.x += 30.0f;
rect.origin.y += 20.0f;
[[self view] setBounds:rect];

The relative image.

Here you say to [self view] that its top left corner now is at the position (30.0, 20.0) but since view1's frame origin starts from (30.0, 20.0), they will coincide.

Additional references (to update with other references if you want)

• UIView Geometry
• UIView Frames and Bounds

About clipsToBounds (source Apple doc)

Setting this value to YES causes subviews to be clipped to the bounds of the receiver. If set to NO, subviews whose frames extend beyond the visible bounds of the receiver are not clipped. The default value is NO.

In other words, if a view's frame is (0, 0, 100, 100) and its subview is (90, 90, 30, 30), you will see only a part of that subview. The latter won't exceed the bounds of the parent view.

masksToBounds is equivalent to clipsToBounds. Instead to a UIView, this property is applied to a CALayer. Under the hood, clipsToBounds calls masksToBounds. For further references take a look to How is the relation between UIView's clipsToBounds and CALayer's masksToBounds?.

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