ios - CGContextClearRect 导致背景颜色为黑色

Question

我有一个 UIButton 子类，我正在使用 drawRect: 绘制边框。选择按钮后，我希望更改背景颜色并删除边框。 (手动绘制边框，因为有时我只需要在一侧画一个边框)

出于某种原因，当我使用 CGContextClearRect 删除已经绘制的边框时，我得到的是黑色背景，而不是我设置的颜色:

- (void)setSelected:(BOOL)selected {
    [super setSelected:selected];

    if (selected) {
        self.allOff = YES;
        self.backgroundColor = self.selectedColor;
        [self setTitleColor:[UIColor whiteColor] forState:UIControlStateSelected];
    } else {
        self.allOff = NO;
        self.backgroundColor = self.defaultColor;
        [self setTitleColor:[OTAColors colorWithRed:163 green:163 blue:163] forState:UIControlStateNormal];
    }

}

- (void)_setup {

    self.opaque = NO;

    self.defaultColor = [[UIColor whiteColor] colorWithAlphaComponent:0.99];
    self.selectedColor = [[OTAColors colorWithRed:33 green:59 blue:70] colorWithAlphaComponent:0.99];

    self.backgroundColor = self.defaultColor;
    [self setTitleColor:[OTAColors colorWithRed:163 green:163 blue:163] forState:UIControlStateNormal];
    self.titleLabel.font = [UIFont fontWithName:OTAFontPFDinTextCondProMedium size:20];
    self.titleLabel.textAlignment = NSTextAlignmentCenter;

}

- (void)drawRect:(CGRect)rect {

    CGFloat borderWidth = 0.7f;
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(ctx, borderWidth);
    UIColor *borderColor = self.borderColor ? self.borderColor : [UIColor blackColor];
    CGContextSetStrokeColorWithColor(ctx, borderColor.CGColor);

    if (!self.allOff) {
        // Left
        if (self.left) {
            CGContextMoveToPoint(ctx, 0, 0);
            CGContextAddLineToPoint(ctx, 0,rect.size.height);
            CGContextStrokePath(ctx);
        }

        // Right
        if (self.right) {
            CGContextMoveToPoint(ctx, rect.size.width, 0);
            CGContextAddLineToPoint(ctx, rect.size.width,rect.size.height);
            CGContextStrokePath(ctx);
        }

        // Top
        if (self.top) {
            CGContextMoveToPoint(ctx, 0, 0);
            CGContextAddLineToPoint(ctx, rect.size.width,0);
            CGContextStrokePath(ctx);
        }

        // Bottom
        if (self.bottom) {
            CGContextMoveToPoint(ctx, 0, rect.size.height);
            CGContextAddLineToPoint(ctx, rect.size.width,rect.size.height);
            CGContextStrokePath(ctx);
        }
    } else {
        CGContextClearRect(ctx, rect);
    }

}

知道为什么会发生这种情况吗？ CGContextClearRect 似乎是导致此问题的原因。

Answer 1

调用 clear rect 会清除所有内容，因此它会恢复为默认的黑色内容。相反，您应该先用背景色填充矩形，然后再为边框绘制适当的线条。