讓視圖單獨顯示某一側的邊框線

有時候需要讓view顯示某一側的邊框線，這時設置layer的border是達不到效果的。在網上查閱資料發現有一個投機取巧的辦法，原理是給view的layer再添加一個layer，讓這個layer充當邊框線的角色。根據這個方法我寫了一個函數，有需要的朋友可以拿去試下。

- (void)setBorderWithView:(UIView *)view top:(BOOL)top left:(BOOL)left bottom:(BOOL)bottom right:(BOOL)right borderColor:(UIColor *)color borderWidth:(CGFloat)width
{
    if (top) {
        CALayer *layer = [CALayer layer];
        layer.frame = CGRectMake(0, 0, view.frame.size.width, width);
        layer.backgroundColor = color.CGColor;
        [view.layer addSublayer:layer];
    }
    if (left) {
        CALayer *layer = [CALayer layer];
        layer.frame = CGRectMake(0, 0, width, view.frame.size.height);
        layer.backgroundColor = color.CGColor;
        [view.layer addSublayer:layer];
    }
    if (bottom) {
        CALayer *layer = [CALayer layer];
        layer.frame = CGRectMake(0, view.frame.size.height - width, view.frame.size.width, width);
        layer.backgroundColor = color.CGColor;
        [view.layer addSublayer:layer];
    }
    if (right) {
        CALayer *layer = [CALayer layer];
        layer.frame = CGRectMake(view.frame.size.width - width, 0, width, view.frame.size.height);
        layer.backgroundColor = color.CGColor;
        [view.layer addSublayer:layer];
    }
}