从 UIImageView 中删除最后一个绘图上下文答案

【问题标题】：Remove last drawing context from UIImageView从 UIImageView 中删除最后一个绘图上下文
【发布时间】：2012-11-20 17:38:25
【问题描述】：

我有这个在UIImageView 上绘图的代码，我想将绘图保存到一个数组中并添加一个删除最后一个绘图的按钮。

我该怎么做？

这是我的代码：

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

    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];

    lastPoint = [touch locationInView:self.view];
    lastPoint.y -= 10;
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    mouseSwiped = YES;

    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];
    currentPoint.y -= 10;

    UIGraphicsBeginImageContext(self.view.frame.size);
    [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10.0);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;
}

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

    if(!mouseSwiped) {
        UIGraphicsBeginImageContext(self.view.frame.size);
        [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10.0);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        drawImage.backgroundColor = [UIColor clearColor];
    }
}

谢谢。

【问题讨论】：

您认为每次收到触摸时都绘制图像是一个好主意。我认为创建一次绘图然后将其保存到磁盘并稍后在收到触摸时使用相同的图像可能是更好和更有效的方法。

标签： iphone objective-c ios uiimageview cgcontext

【解决方案1】：

       Declare on NSMutableArray object in .h file
         // in .h file
           NSMutableArray *storage;

        // in .m file and initialize in view did load
           storage = [[NSMutableArray alloc]init];

 - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
                if ([self.storage count] < MAX_LINE) {
                if(!mouseSwiped) {
                    UIGraphicsBeginImageContext(self.view.frame.size);
                    [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
                    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
                    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10.0);
                    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
                    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                    CGContextStrokePath(UIGraphicsGetCurrentContext());
                    CGContextFlush(UIGraphicsGetCurrentContext());
                    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
                    UIGraphicsEndImageContext();
                    drawImage.backgroundColor = [UIColor clearColor];
                }
                NSString *path = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString      stringWithFormat:@"%d_drawslide__.png", [self.storage count]]];
                        [self.storage addObject:path];
                        NSMutableDictionary *params = [[NSMutableDictionary alloc] initWithObjectsAndKeys:drawImage.image, path, nil];
                    [NSThread detachNewThreadSelector:@selector(backuppmage:) toTarget:self withObject:params];
                        [params release];
            }

 }

-(void) backuppmage:(NSMutableDictionary *) params
  {
        NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
        for (NSString *key in params) {
              UIImage *image = (UIImage *)[params objectForKey:key];
              [UIImagePNGRepresentation(image) writeToFile:key atomically:YES];
              }
         [pool drain];


  }

        // add this method to button click
-(IBAction) undoEraseDrawing:(id) sender {

            if (!isErased && [self.storage count] > 0) {

                [self.storage removeObject:[self.storage lastObject]];

            }

            if ([self.storage count] > 0 && [self.storage lastObject] != nil) {
                drawImage.image = [self getImageWithURL:(NSString *)[self.storage lastObject]];
            } else {
                drawImage.image = nil;
            }
            isErased = NO;

    }


-(UIImage *) getImageWithURL:(NSString *)url
    {
            return [UIImage imageWithContentsOfFile:url];
    }

【讨论】：