添加自定义手势识别：TapGesture

1.确认userInteractionEnabled = YES
2.确认添加了
3.添加代码：

    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapResign)];

    [backgroundImageView addGestureRecognizer:tap];
    backgroundImageView.userInteractionEnabled = YES;

    tap.numberOfTapsRequired = 1;
4.OK！