Question

我正在参与Big Nerd Ranch的iOS编程指南中关于UIView子类化的一章中的挑战。

下面我有一些代码用随机颜色绘制同心圆。并且，在摇晃之后，它应该将它们全部变为红色。它不是因为设置红色后，再次调用drawRect并重做随机颜色循环。

实现这个的正确方法是将随机颜色循环移出drawRect吗？我是否设置了一个信号量（凌乱）以确保循环只运行一次？

感谢您的建议。

- (void)setCircleColor:(UIColor *)clr
{
    circleColor = clr;
    [self setNeedsDisplay];
}

- (BOOL) canBecomeFirstResponder
{
    return YES;
}

- (void)motionBegan:(UIEventSubtype)motion withEvent:(UIEvent *)event
{
    if (motion == UIEventSubtypeMotionShake) {
        [self setCircleColor:[UIColor redColor]];
    }
}

-(void)drawRect:(CGRect)dirtyRect
{
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect bounds = [self bounds];

    // Figure out the center of the bounds rectangle
    CGPoint center;
    center.x = bounds.origin.x + bounds.size.width / 2.0;
    center.y = bounds.origin.y + bounds.size.height / 2.0;

    float maxRadius = hypot(bounds.size.width, bounds.size.height) / 2.0;

    CGContextSetLineWidth(ctx, 10);

    // Set up an array of colors
    UIColor *red = [UIColor redColor];
    UIColor *green = [UIColor greenColor];
    UIColor *yellow = [UIColor yellowColor];

    NSArray *colors = [[NSArray alloc]initWithObjects:red, green, yellow, nil];

    // Draw concentric circles from the outside in

    for (float currentRadius = maxRadius; currentRadius > 0; currentRadius -= 20) {
        CGContextAddArc(ctx, center.x, center.y, currentRadius, 0.0, M_PI * 2, YES);

        // Random index for colors array
        NSUInteger randomIndex = arc4random() % [colors count];
        [self setCircleColor:[colors objectAtIndex:randomIndex]];

        [[self circleColor] setStroke];

        // Perform drawing; remove path
        CGContextStrokePath(ctx);
    }

    NSString *text = @"You are getting sleepy.";
    UIFont *font = [UIFont boldSystemFontOfSize:28];

    CGRect textRect;

    textRect.size = [text sizeWithFont:font];

    // Let's put that string in the center of the view
    textRect.origin.x = center.x - textRect.size.width / 2.0;
    textRect.origin.y = center.y - textRect.size.height / 2.0;

    [[UIColor blackColor] setFill];

    // Draw a shadow
    CGSize offset = CGSizeMake(4, 3);
    CGColorRef color = [[UIColor darkGrayColor] CGColor];
    CGContextSetShadowWithColor(ctx, offset, 2.0, color);

    [text drawInRect:textRect withFont:font];



}

-(id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setBackgroundColor:[UIColor clearColor]];
        [self setCircleColor:[UIColor lightGrayColor]];
    }
    return self;
}
@end

Answer 1

制作一个 BOOL isshake 并在摇动设备后取消随机颜色，圆圈将保持红色，您可以在另一个动作时将其重置。

motionBegan，setStroke和drawRect正确用法

1 个答案: