如果drawRect被覆盖，iOS子视图将显示为黑色矩形

Question

我有一个故事板，它加载并加载自定义UIView。此外，还会向情节提要中的视图添加一个子视图。它工作得很好，直到我覆盖了子视图的drawRect方法，然后我只看到了一个黑色矩形而不是子视图。这是代码：

#import <UIKit/UIKit.h>
#import "MySubview.h"
@interface MyView : UIView
@end

---

#import "MyView.h"
@implementation MyView
- (void) awakeFromNib
{
    CGRect frame = [self frame];
    MySubview* sv = [[MySubview alloc] initWithFrame:frame];
    [self addSubview:sv];
}
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}
@end

---

#import <UIKit/UIKit.h>
@interface MySubview : UIView
@property (retain, nonatomic) NSString* text;
@property (retain, nonatomic) UILabel* label;
@end

---

#import "MySubview.h"
@implementation MySubview
@synthesize text, label;

- (void)attachLabel
{
    text = @"Hello";
    label = [[UILabel alloc] init];
    [label setText:text];
    [label setFont:[UIFont fontWithName:@"Futura" size:18]];
    [label setBackgroundColor:[UIColor clearColor]];
    [label sizeToFit];
    CGRect labelFrame = label.frame;
    labelFrame.origin.x = (self.frame.size.width  - labelFrame.size.width) / 2;
    labelFrame.origin.y = (self.frame.size.height - labelFrame.size.height) / 2;
    label.frame = labelFrame;
    [self addSubview:label];
}
- (void)awakeFromNib
{
    [self attachLabel];
}
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self attachLabel];
    }
    return self;
}
// Works if I comment this out!
- (void)drawRect:(CGRect)rect
{
}
@end

更新-在下面添加了绘图代码：

- (void)drawRectWithRoundBorders:(CGRect)rect
{
    [super drawRect:rect];
    // Parameters used for drawing.
    const CGFloat lineWidth = 5;
    const CGFloat shadowOffset = 3;
    const CGFloat shadowBlur = 4;
    const CGFloat spaceToBB = 10;   // Space to the bounding box of this view.
    const CGFloat cornerRadii = 5;
    const CGFloat lineColor[4] = { 0, 0, 0, 1 };
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(ctx, lineWidth);
    CGContextSetStrokeColor(ctx, lineColor);
    CGContextSetShadow(ctx, CGSizeMake(shadowOffset, shadowOffset), shadowBlur);
    CGRect innerRect = rect;
    innerRect.size.width -= 2*spaceToBB;
    innerRect.size.height -= 2*spaceToBB;
    innerRect.origin.x += spaceToBB;
    innerRect.origin.y += spaceToBB;
    UIBezierPath *path = 
    [UIBezierPath bezierPathWithRoundedRect:innerRect 
                          byRoundingCorners:UIRectCornerAllCorners 
                                cornerRadii:CGSizeMake(cornerRadii, cornerRadii)
     ];
    CGContextAddPath(ctx, path.CGPath);
    CGContextStrokePath(ctx);
}

- (void)drawRect:(CGRect)rect
{
    [self drawRectWithRoundBorders:rect];
}

更新

当我首先用一些颜色填充子视图的边界框时，它似乎起作用。

CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat white[] = {1, 1, 1, 0.5};
CGContextSetFillColor(ctx, white);
CGContextAddRect(ctx, rect);
CGContextFillPath(ctx);

Answer 1

只需在initWithFrame:方法中添加[self setOpaque:NO]即可。

Answer 2

这是因为您的drawRect什么都没做。如果要进行自定义绘图，可以替代drawRect。因此：

• 如果不想进行自定义绘图，则不要替代drawRect
• 如果你真的想做自定义绘图，那么实际上在drawRect中做一些事情