在UIImageView问题中画一条线 [英] draw a line in UIImageView problem

问题描述

在我的应用程序中，我可以通过下面的代码在UIImageView中绘制一条线，我想重新绘制线甚至更长的时间，当我调用该函数，但是，输出不是预期的，它只会绘制一个新的行和删除旧的，长度保持不变jus y位置不同，我不知道我的代码是哪一行是错误或我不能以正确的方式理解CGContext类，请帮我我刮头我的头一天并且找不到问题

In my application i can draw a line in a UIImageView by the code below,and i want redraw the line even longer when i call the function,however,the output come out is not as expected,it will just draw a new line and remove the old one,the length is remain the same jus the y position different,i dont know which line of my code is wrong or i havent understand the CGContext class in correct way,please help i have scratch my head all the days and cannot find out the problem

- (void) drawLine {
    lastPoint = currentPoint;
    lastPoint.y -= 40;

    //drawImage is a UIImageView declared at header
    UIGraphicsBeginImageContext(drawImage.frame.size);
    [drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width, drawImage.frame.size.height)];

    //sets the style for the endpoints of lines drawn in a graphics context
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSetLineCap(ctx, kCGLineCapButt);
    //sets the line width for a graphic context
    CGContextSetLineWidth(ctx,2.0);
    //set the line colour
    CGContextSetRGBStrokeColor(ctx, 1.0, 0.0, 0.0, 1.0);
    //creates a new empty path in a graphics context
    CGContextBeginPath(ctx);
    //begin a new path at the point you specify
    CGContextMoveToPoint(ctx, currentPoint.x, currentPoint.y);
    //Appends a straight line segment from the current point to the provided point 
    CGContextAddLineToPoint(ctx, currentPoint.x,lastPoint.y);
    //paints a line along the current path
    CGContextStrokePath(ctx);
    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    currentPoint = lastPoint;
}

推荐答案

CGContextAddLineToPoint(ctx, currentPoint.x,lastPoint.y);

应为：

CGContextAddLineToPoint(ctx, lastPoint.x,lastPoint.y);

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