这是一个从 adam-siton/AUISelectiveBordersView 改编的 cocoapod
UILabel* label = [[UILabel alloc] initWithFrame: CGRectMake(0,0, 200, 30)];
label.selectiveBorderWidth = 1.0f;
label.selectiveBorderFlags = AUISelectiveBorderTop | AUISelectiveBorderLeft;
label.selectiveBorderColor = [UIColor redColor];
//then add the label to another view