[转载]在uiview上画线.写字(转)

#import "WhiteBoardView.h"

@implementation WhiteBoardView

- (id)initWithFrame:(CGRect)frame {        //1
    if (self = [super initWithFrame:frame]) {        //2

        self.backgroundColor = [UIColor clearColor];        //3
        self.opaque=0.5;

        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        whiteBoardContext = CGBitmapContextCreate(NULL, self.frame.size.width, self.frame.size.height, 8,
                                                  4 *self.frame.size.width, colorSpace, kCGImageAlphaPremultipliedFirst);
        CGColorSpaceRelease(colorSpace) ;

        whiteBoardLayer = CGLayerCreateWithContext(whiteBoardContext, self.frame.size, NULL);
        CGContextRef layerContext = CGLayerGetContext(whiteBoardLayer);

        CGContextSetLineWidth(layerContext, 20);
        CGContextSetLineCap(layerContext, kCGLineCapRound);
        CGContextSetRGBStrokeColor(layerContext, 0.0,0.0,0.0,1);

        //UIImageView *imgView=[[UIImageView alloc]initWithImage:[UIImage imageNamed:@"1.jpg"]];
//        imgView.frame=CGRectMake(150, 150, 150, 150);
//        [self insertSubview:imgView atIndex:0];

    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    CGContextRef currentContext = UIGraphicsGetCurrentContext();

    CGImageRef image = CGBitmapContextCreateImage(whiteBoardContext);
    CGContextDrawImage(currentContext, [self bounds], image);
    CGContextDrawLayerInRect(currentContext    , [self bounds], whiteBoardLayer);

}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *theTouch = [touches anyObject];
    if ([theTouch tapCount] == 2)
    {
        CGContextClearRect(whiteBoardContext, [self bounds]);
        [self setNeedsDisplay];
    }else
    {
        [self touchesMoved:touches withEvent:event];
    }
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *theTouch = [touches anyObject];
    CGPoint currentTouchLocation = [theTouch locationInView:self];
    CGPoint lastTouchLoacation = [theTouch previousLocationInView:self];
    CGContextRef layerContext = CGLayerGetContext(whiteBoardLayer);
    CGContextBeginPath(layerContext);
    CGContextMoveToPoint(layerContext, lastTouchLoacation.x, lastTouchLoacation.y);
    CGContextAddLineToPoint(layerContext, currentTouchLocation.x, currentTouchLocation.y);
    CGContextStrokePath(layerContext);

    [self setNeedsDisplay];

}

- (void)dealloc {
    CGContextRelease(whiteBoardContext);                                    //35
    CGLayerRelease(whiteBoardLayer);                                        //46
    [super dealloc];
}

@end