drawRect不想画任何东西 [英] drawRect Doesn't want to draw anything

问题描述

我在故事板上有一个ViewController.我已经使用界面生成器在屏幕底部设置了一个工具栏.我已经将自定义视图设置为覆盖drawRect的视图.但是，对于我一生来说，我无法任何事情出现在该drawRect调用的屏幕上. drawRect本身就很好，但是屏幕上什么都没显示.

I have a ViewController on storyboard. I have used the interface builder to set a toolbar at the bottom of the screen. I have set the custom view to a view overrides drawRect. However, for the life of me, I cannot get anything ever to show up on screen called from that drawRect. drawRect itself is called just fine, but nothing shows up on screen.

此外，我还有一个ViewController及其方法，该方法使用AVCaptureSession将其背景从摄像机输入切换为实时取景.我曾怀疑这可能是导致错误的原因，但是在删除所有AVCaptureSession的引用之后，我仍然无法使它正常工作.

Also, I have this ViewController with a method that uses AVCaptureSession to toggle its background to a live view from camera input. I had suspected that this might have been the cause for error, but after removing all references of AVCaptureSession, I still cannot get this to work.

抱歉，我的写作和/或缺乏逻辑，我现在没有任何睡眠.

Sorry for my writing and/or lack of logic, I don't have any sleep right now.

这是一个不起作用的小代码示例.里面的每个方法都被调用，但是什么也没显示.

Here is a small example of code that won't work. Every method inside gets called, but nothing is to show.

- (void)drawRect:(CGRect)rect {
    [super drawRect:rect];

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);

    // Draw them with a 2.0 stroke width so they are a bit more visible.
    CGContextSetLineWidth(context, 2.0);

    CGContextMoveToPoint(context, 0,0); //start at this point

    CGContextAddLineToPoint(context, 100, 100); //draw to this point

    // and now draw the Path!
    CGContextStrokePath(context);
}

推荐答案

UIView的文档说，如果您要覆盖UIView，请不要调用[super drawRect].删除该电话！众所周知，它会引起奇怪的行为.

The documentation for UIView says to not call [super drawRect] if you're overriding UIView. Remove that call! It's been known to cause strange behaviour.

根据文档:

如果直接子类化UIView，则此方法的实现 不需要调用超级.但是，如果您将一个子类 不同的视图类，您应该在您的某个时候调用super 实施.

If you subclass UIView directly, your implementation of this method does not need to call super. However, if you are subclassing a different view class, you should call super at some point in your implementation.

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