UIView 绘画

最近的一个项目是与画画相关的 在这里简单总结下UIView的绘画方面的东西吧

首先必须写的方法肯定是drawRect,但是我们在代码中并不会直接去调用这个方法,因为这个方法是UIView在重绘的时候,自己调用的.

我们可以在代码中通过调用 setNeedsDisplayInRect 来强制View刷新.

下面说一下怎么在View上面画线,首先是要在响应用户在屏幕上滑动过程的三个方法

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{        UITouch *touch = [touches anyObject];        previousPoint1 = [touch locationInView:self];    previousPoint2 = [touch locationInView:self];    currentPoint = [touch locationInView:self];    //NSLog(@"pre %f %f",currentPoint.x,currentPoint.y);        [bufferArray removeAllObjects];     [self touchesMoved:touches withEvent:event];}-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{        UITouch *touch  = [touches anyObject];        previousPoint2  = previousPoint1;    previousPoint1  = currentPoint;    currentPoint    = [touch locationInView:self];        if(drawStep == REDO || drawStep == UNDO)    {        if(isDraw)            drawStep = DRAW;        else            drawStep = ERASE;    }    [self calculateMinImageArea:previousPoint1 :previousPoint2 :currentPoint];    }-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{    UIGraphicsBeginImageContext(self.bounds.size);    [self.layer renderInContext:UIGraphicsGetCurrentContext()];    curImage = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();        NSDictionary *lineInfo = [NSDictionary dictionaryWithObjectsAndKeys:curImage, @"IMAGE",                              nil];        if(lineArray.count == 20)    {        [lineArray removeObjectAtIndex:0];    }    [lineArray addObject:lineInfo];}- (void) calculateMinImageArea:(CGPoint)pp1 :(CGPoint)pp2 :(CGPoint)cp{        // calculate mid point    CGPoint mid1    = midPoint(pp1, pp2);    CGPoint mid2    = midPoint(cp, pp1);        CGMutablePathRef path = CGPathCreateMutable();    CGPathMoveToPoint(path, NULL, mid1.x, mid1.y);    CGPathAddQuadCurveToPoint(path, NULL, pp1.x, pp1.y, mid2.x, mid2.y);    CGRect bounds = CGPathGetBoundingBox(path);    CGPathRelease(path);        CGRect drawBox = bounds;            //Pad our values so the bounding box respects our line width    drawBox.origin.x        -= self.lineWidth * 1;    drawBox.origin.y        -= self.lineWidth * 1;    drawBox.size.width      += self.lineWidth * 2;    drawBox.size.height     += self.lineWidth * 2;        UIGraphicsBeginImageContext(drawBox.size);    [self.layer renderInContext:UIGraphicsGetCurrentContext()];    curImage = UIGraphicsGetImageFromCurrentImageContext();    //[curImage retain];    UIGraphicsEndImageContext();        [self setNeedsDisplayInRect:drawBox];        //http://stackoverflow.com/a/4766028/489594    [[NSRunLoop currentRunLoop] runMode: NSDefaultRunLoopMode beforeDate: [NSDate date]];}

- (void)drawRect:(CGRect)rect{        switch (drawStep) {        case DRAW:        {            [curImage drawAtPoint:CGPointMake(0, 0)];            CGPoint mid1 = midPoint(previousPoint1, previousPoint2);            CGPoint mid2 = midPoint(currentPoint, previousPoint1);            CGContextRef context = UIGraphicsGetCurrentContext();                        [self.layer renderInContext:context];            CGContextMoveToPoint(context, mid1.x, mid1.y);            CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);            if(previousPoint1.x == previousPoint2.x && previousPoint1.y == previousPoint2.y && previousPoint1.x == currentPoint.x && previousPoint1.y == currentPoint.y)            {                CGContextSetLineCap(context, kCGLineCapRound);                            }            else            {                CGContextSetLineCap(context, kCGLineCapRound);                            }            CGContextSetLineWidth(context, self.lineWidth);            CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);            CGContextSetAlpha(context, self.lineAlpha);            CGContextStrokePath(context);            [super drawRect:rect];            //[curImage release];            break;        }}

上面就是画线的代码片段 最基本的步骤就是 在move的时候 需要创建CGMutablePathRef 来保存移动的路径 并且调用下面这段代码来将当前的画面保存在curImg变量中,但是这个时候还看不到,因为View并没有刷新 在调用了 setNeedsDisplay之后 需要对curImg进行绘制 让用户看到刷新后的View

    UIGraphicsBeginImageContext(drawBox.size);    [self.layer renderInContext:UIGraphicsGetCurrentContext()];    curImage = UIGraphicsGetImageFromCurrentImageContext();    //[curImage retain];    UIGraphicsEndImageContext();

上面这段代码 可以看作是截图功能,在很多地方都可以用

好困 暂时没兴趣写了