App项目紧急加入整体页面置灰处理，这个功能呢，其实还算比较常规吧，在一些特殊日子中，为了悼念，大部分App会有置灰操作，有些只置灰首页，有的是置灰整体页面。

对于置灰操作，如果是每次都更新版本，肯定就来不及，一般处理方式为后台设置按钮开关，处理对应日子开启置灰操作。由于是后台处理，通过接口返回结果，那么看下iOS端实现方法

1.使用runtime方法交换机制处理，以图片加载为例

+ (void)load {
    Method originalMethod = class_getInstanceMethod([self class], @selector(setImage:));
    Method swizzledMethod = class_getInstanceMethod([self class], @selector(custom_setImage:));
    method_exchangeImplementations(customMethod, originMethod);//方法交换
}

- (void)custom_setImage:(UIImage *)image {
    //读取接口返回是否置灰
    if (DEFAULTES_GET_OBJECT(@"isGrey")) {
        [self custom_setImage:[self change_greyImage:image]];
    } else {
        [self custom_setImage:image];
    }
}

- (UIImage *)change_greyImage:(UIImage *)image {
        //UIKBSplitImageView是为了键盘
    if (image == nil || [self.superview isKindOfClass:NSClassFromString(@"UIKBSplitImageView")]) {
        return image;
    }
    
    //滤镜处理
    //CIPhotoEffectNoir黑白
    //CIPhotoEffectMono单色
    NSString *filterName = @"CIPhotoEffectMono";
    CIFilter *filter = [CIFilter filterWithName:filterName];
    CIImage *inputImage = [[CIImage alloc] initWithImage:image];
    [filter setValue:inputImage forKey:kCIInputImageKey];
    CGImageRef cgImage = [self.filterContext createCGImage:filter.outputImage fromRect:[inputImage extent]];
    UIImage *resultImg = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    return resultImg;
}

- (CIContext *)filterContext {
    CIContext *con = objc_getAssociatedObject(self, @selector(filterContext));
    if (!con) {
        con = [[CIContext alloc] initWithOptions:nil];
        self.filterContext = con;
    }
    return con;
}

- (void)setFilterContext:(CIContext *)filterContext {
    objc_setAssociatedObject(self, @selector(filterContext), filterContext, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

2.添加一个view，里面不接收任何点击事件（该做法只支持iOS12及12以上，根据实际情况使用）

@interface UIGreyViewOverLay : UIView

@end

@implementation UIGreyViewOverLay

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
}
*/
-(UIView*)hitTest:(CGPoint)point withEvent:(UIEvent *)event{
   return nil;
}
@end

//使用,把他直接覆盖在最顶层window.view即可:

- (void)initLaunchViewController{
    UIView *contentView = [AppDelegate defaultView];
    
    //app整体置灰
    if (DEFAULTES_GET_OBJECT(@"isGrey")){
        UIViewOverLay *overlay = [[UIViewOverLay alloc]initWithFrame:self.window.bounds];
        overlay.translatesAutoresizingMaskIntoConstraints = false;
        overlay.backgroundColor = [UIColor lightGrayColor];
        overlay.layer.compositingFilter = @"saturationBlendMode";
        [contentView addSubview:overlay];
    }
    
    LaunchViewController *launchController = [[LaunchViewController alloc]init];
    [contentView addSubview:launchController.view];
    launchController.view.frame = contentView.frame;
}
+ (UIView *)defaultView {
    UIView *view;
    for (UIWindow * window in [UIApplication sharedApplication].windows) {
        if (!window.hidden
            && (window.windowLevel < UIWindowLevelStatusBar)) {
            view = window;
        }
    }
    return view;
}