我在界面生成器中声明了一个 UIButton，其插座设置如下：
@property (weak, nonatomic) IBOutlet UIButton *loginButton;
在我插入子视图之前它工作正常。然后它停止响应。这是违规行：
[self.loginButton insertSubview:_gradientButtonView atIndex:0];
将其注释掉会使按钮再次起作用。下面是所有涉及的代码（使用很棒的 SSToolkit 和 UIColor 上的自定义类别）：
SSGradientView *_gradientButtonView = [[SSGradientView alloc] initWithFrame:self.loginButton.layer.bounds];
_gradientButtonView.autoresizingMask = UIViewAutoresizingFlexibleWidth;
_gradientButtonView.topBorderColor = [UIColor colorWithRed:0.558f green:0.599f blue:0.643f alpha:1.0f];
_gradientButtonView.topInsetColor = [UIColor colorWithWhite:1.0f alpha:0.3f];
_gradientButtonView.colors = [NSArray arrayWithObjects:[UIColor from_hex:@"E6E7E8"], [UIColor from_hex:@"A7A9AC"], nil];
_gradientButtonView.layer.cornerRadius = 5;
self.loginButton.layer.cornerRadius = 5;
self.loginButton.titleLabel.shadowOffset = CGSizeMake(0, 1);
[self.loginButton setTitleShadowColor:[UIColor whiteColor] forState:UIControlStateNormal];
self.loginButton.layer.masksToBounds = YES;
_gradientView.bottomBorderColor = [UIColor colorWithRed:0.428f green:0.479f blue:0.520f alpha:1.0f];
_gradientButtonView.clipsToBounds = YES;
_gradientButtonView.userInteractionEnabled = YES;
[self.loginButton insertSubview:_gradientButtonView atIndex:0];
self.loginButton.userInteractionEnabled = YES;