如果启用了自动布局，则不会调用drawRect

Question

XCode 5, Mac OS 10.9.4, iOS 7.

I'm working on a project that uses a lot of view “cells” that go into Scroll and Table Views. Each “cell” View is in separate .xib file and is loaded something like this:

+(instancetype) newViewOfKind:(NSString*) theViewKind withItemInfo:(LTWItemInfo*) theItemInfo
{
NSString*   myClassName;
LTWItemView*    myNewCell;

myClassName = NSStringFromClass([self class]);
myNewCell = [[super class] newViewOfKind:theViewKind withItemInfo:theItemInfo andNIBBaseName:myClassName];

if (myNewCell.pItemActivityIndicator != nil)
    myNewCell.pItemActivityIndicator.hidesWhenStopped = YES;

myNewCell.pItemDownloadImageLoadedFlag = NO;
myNewCell.pItemDownloadImage = nil;
[myNewCell setItemInfo:theItemInfo];

return myNewCell;
}

This works well and is being used in lots of places in the App.

This project was originated before Auto-Layout was around and it is off in all the cell .xib files.

The .xib file for each of these views has a “standard” layout that looks like this:

LTWItemView.xib — Auto-Layout off.

LTWItemView - The View Class Itself.

Subview of LTWItemView: “FrameRect” - View of Class “LTWDrawFrameView” (this is a normal view, but drawRect overridden to draw a frame around the view).

Subviews of “FrameRect” view, other views UILabels, UIImageView's, UIButton's, etc.

The problem is that the drawRect method in “FrameRect” does not get called and its background colour doesn't get set either. When I first created this view, I had Auto-Layout enabled by mistake and in this case the background colour is set ok and drawRect is called. I've verified this.

The problem is that if I enable Auto-Layout, it causes problems elsewhere and it's too big a job to convert the project to use it.

Also, inside some of “FrameRect” views, there are other, smaller LTWDrawFrameView's and these draw their frame and set their background colours ok. It seems like it just doesn't work with the first subview inside the view loaded from the nib.

Any ideas on how to solve this would be greatly appreciated.

---

I've worked around the problem by adding a "dummy" view as the first subview of the Cell View in the .xib file and putting the "FrameRect" (and all its subviews) inside this view. This seems to work fine and solves my immediate problem, but I'd love to know if there is a better fix for this.

Answer 1

我没有完全解决您的问题，但是通常需要调用其drawRectFunction的视图应该将其contentMode设置为UIViewContentModeRedraw

yourView.contentMode = UIViewContentModeRedraw;

Answer 2

Disambigous layout can cause that. For example, you specified NSLayoutConstraint's about the vertical placement of the view, but didn't say anything about horizontal. The situation can be treacherous as UIKit tries it's best and places the view at least somewhere, but drawRect: is not called.