iOS（CoreGraphics）画带箭头的框
自己画带箭头的框，需要导入CoreGraphics.framwork库
新建一个集成UIView 的类，对UIView中的drawRect:(CGRect)rect方法重写如下。
绘图操作
//绘制带箭头的矩形
-(void)drawArrowRectangle:(CGRect) frame
{
// 获取当前图形，视图推入堆栈的图形，相当于你所要绘制图形的图纸
CGContextRef ctx =UIGraphicsGetCurrentContext();
// 创建一个新的空图形路径。
CGContextBeginPath(ctx);
//启始位置坐标x，y
CGFloat origin_x = frame.origin.x;
CGFloat origin_y = frame.origin.y;
//第一条线的位置坐标
CGFloat line_1_x = frame.size.width;
CGFloat line_1_y = origin_y;
//第二条线的位置坐标
CGFloat line_2_x = line_1_x;
CGFloat line_2_y = frame.size.height;
//第三条线的位置坐标
CGFloat line_3_x = origin_x + 20;
CGFloat line_3_y = line_2_y;
//尖角的顶点位置坐标
CGFloat line_4_x = line_3_x - 5;
CGFloat line_4_y = line_2_y + 10;
//第五条线位置坐标
CGFloat line_5_x = line_4_x - 5;
CGFloat line_5_y = line_3_y;
//第六条线位置坐标
CGFloat line_6_x = origin_x;
CGFloat line_6_y = line_2_y;
CGContextMoveToPoint(ctx, origin_x, origin_y);
CGContextAddLineToPoint(ctx, line_1_x, line_1_y);
CGContextAddLineToPoint(ctx, line_2_x, line_2_y);
CGContextAddLineToPoint(ctx, line_3_x, line_3_y);
CGContextAddLineToPoint(ctx, line_4_x, line_4_y);
CGContextAddLineToPoint(ctx, line_5_x, line_5_y);
CGContextAddLineToPoint(ctx, line_6_x, line_6_y);
CGContextClosePath(ctx);
UIColor *costomColor = [UIColorcolorWithWhite:0alpha:0.8];
CGContextSetFillColorWithColor(ctx, costomColor.CGColor);
CGContextFillPath(ctx);
}
//重写绘图，调用刚才绘图的方法
-(void)drawRect:(CGRect)rect
{
CGRect frame = rect;
frame.size.height = frame.size.height -20;
rect = frame;
//绘制带箭头的框框
[selfdrawArrowRectangle:rect];
}
