绘图应用程序的颜色

Question

对于我的应用，我需要实现一个绘图空间。在在线教程的帮助下，我成功绘图。但现在的挑战是用不同的颜色来绘制。我在下面编写了代码，但它不起作用，我不明白为什么它不起作用。它只涂成黑色。 我的 UIView.m 中有以下内容

    - (void)drawBitmap
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, 0.0);

    if (!incrementalImage) // first time; paint background white
    {
        UIBezierPath *rectpath = [UIBezierPath bezierPathWithRect:self.bounds];
        [[UIColor whiteColor] setFill];
        [rectpath fill];
    }
    [incrementalImage drawAtPoint:CGPointZero];
    [color setStroke];
    [path stroke];
    incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}

- (void)color1 {
    color = [UIColor greenColor];
}

- (void)color2 {
    color = [UIColor yellowColor];
}

我从 ViewController.m 调用函数

- (IBAction)drawGreen:(id)sender {
    SmoothedBIView *smoothView = [[SmoothedBIView alloc]init];
    [smoothView color1];
}

- (IBAction)drawYellow:(id)sender {
    SmoothedBIView *smoothView = [[SmoothedBIView alloc] init];
    [smoothView color2];
}

感谢您的帮助！

Answer 1

我怀疑虽然您创建了一个位图上下文，但您实际上并没有绘制它.. 试试这个

    - (void)drawBitmap
    {

       CGContextRef ctx = UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, 0.0);//changed

       UIGraphicsPushContext(ctx);//changed

        if (!incrementalImage) // first time; paint background white
        {
            UIBezierPath *rectpath = [UIBezierPath bezierPathWithRect:self.bounds];
            [[UIColor whiteColor] setFill];
            [rectpath fill];
        }
        [incrementalImage drawAtPoint:CGPointZero];
        [color setStroke];
        [path stroke];
        incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsPopContext(ctx); //changed

        UIGraphicsEndImageContext();
    }