1

我正在为 iOS 创建绘图应用程序。为了画一些东西，我使用了本教程中的代码：http ://www.raywenderlich.com/18840/how-to-make-a-simple-drawing-app-with-uikit

我用于绘图的代码如下：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];
    lastPoint = [touch locationInView:self.view];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = YES;
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];

    UIGraphicsBeginImageContext(self.view.frame.size);
    [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush );
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
    CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeNormal);

    CGContextStrokePath(UIGraphicsGetCurrentContext());
    self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    [self.tempDrawImage setAlpha:opacity];
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;

    NSLog(@"Moved");
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    if(!mouseSwiped) {
        UIGraphicsBeginImageContext(self.view.frame.size);
        [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, opacity);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }

    UIGraphicsBeginImageContext(self.mainImage.frame.size);
    [self.mainImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
    [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:opacity];
    self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext();
    self.tempDrawImage.image = nil;
    UIGraphicsEndImageContext();
}

我的问题如下：这段代码在模拟器和我的 iPhone 5 上运行良好，但是当我在 iPad 2 上运行它时，它运行不佳。我的意思是当触摸被移动时，它只会每 3 秒或类似的东西在屏幕上绘制一次（它不是连续的）。此外，当我在不抬起手指的情况下继续移动手指时，应用程序会在一段时间后崩溃。

我想这是一个性能问题。但为什么？你知道我该如何解决吗？

4

2 回答 2

3

问题是你一直在打电话[self.tempDrawImage.image drawInRect:]。此调用在 CPU 上渲染图像并且非常慢。您不必要地开始和结束图像上下文。请改用此代码，我在 iPad 2 上对其进行了测试，并且运行顺畅。

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];
    lastPoint = [touch locationInView:self.view];

    UIGraphicsBeginImageContext(self.view.frame.size);
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = YES;
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];

    CGContextRef ctxt = UIGraphicsGetCurrentContext();
    CGContextMoveToPoint(ctxt, lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(ctxt, currentPoint.x, currentPoint.y);
    CGContextSetLineCap(ctxt, kCGLineCapRound);
    CGContextSetLineWidth(ctxt, brush );
    CGContextSetRGBStrokeColor(ctxt, red, green, blue, 1.0);
    CGContextSetBlendMode(ctxt,kCGBlendModeNormal);

    CGContextStrokePath(ctxt);
    self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    [self.tempDrawImage setAlpha:opacity];

    lastPoint = currentPoint;
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesCancelled:touches withEvent:event];

    UIGraphicsEndImageContext();

    if(!mouseSwiped)
    {
        self.tempDrawImage.image = nil;
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    if(!mouseSwiped) {
        UIGraphicsEndImageContext();

        UIGraphicsBeginImageContext(self.view.frame.size);
        [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, opacity);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        self.tempDrawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }

    UIGraphicsBeginImageContext(self.mainImage.frame.size);
    [self.mainImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
    [self.tempDrawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height) blendMode:kCGBlendModeNormal alpha:opacity];
    self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext();
    self.tempDrawImage.image = nil;
    UIGraphicsEndImageContext();
}
于 2013-10-14T17:16:02.110 回答
2

是的，但是这样你会遇到内存问题......内存警告和崩溃。

如果你想尝试，画 50 到 150 条线，你可以看到它是如何导致内存问题的。

如果要解决此问题，请在 touchesEnded 方法中将其更改为：

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {




UIGraphicsEndImageContext();        //<----this is correct 
if(!mouseSwiped) {

    //UIGraphicsEndImageContext();  <--- this is the issue

然后完美！

于 2013-10-19T08:41:20.717 回答