特殊情况：结合SDWebImage使用 about swifttheme HOT 4 CLOSED

[self.avatar sd_setBackgroundImageWithURL:[NSURL URLWithString:self.avatar]
                                     forState:UIControlStateNormal
                             placeholderImage:[UIImage imageWithName:imageName]];

- (void)theme_setBackgroundImageWithURL:(NSURL *)url
                            forState:(UIControlState)state
              placeholderImageName:(NSString *)imageKeyPath {
    [self theme_setBackgroundImage:[ThemeImagePicker pickerWithKeyPath:imageKeyPath] forState:state];
    NSString *imageName = [ThemeManager stringForKeyPath:imageKeyPath];
    @weakify(self);
    [self sd_setBackgroundImageWithURL:[self thumbnailImageURL:url]
                              forState:UIControlStateNormal
                      placeholderImage:[UIImage imageWithName:imageName]
                             completed:
                                 ^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                                     @strongify(self);
                                     if (!error) {
                                         NSMutableDictionary *dict = [self.themePickers mutableCopy];
                                         [dict setValue:nil forKey:@"setBackgroundImage:forState:"];
                                         self.themePickers = [dict copy];
                                     }
                                 }];
}

NSString *imageName = [ThemeManager stringForKeyPath:imageKeyPath];
[UIImage imageWithName:imageName];
// 可以替换为：
[ThemeManager imageForKeyPath:imageKeyPath];

NSMutableDictionary *dict = [self.themePickers mutableCopy];
[dict setValue:nil forKey:@"setBackgroundImage:forState:"];
self.themePickers = [dict copy];
// 可以替换为：
[self theme_setBackgroundImage:nil forState:UIControlStateNormal]; // 现在类型不支持，我改一下

[self theme_setBackgroundImage:[ThemeImagePicker pickerWithKeyPath:imageKeyPath] forState:state];
@weakify(self);
[self sd_setBackgroundImageWithURL:[self thumbnailImageURL:url]
                          forState:state
                  placeholderImage:[ThemeManager imageForKeyPath:imageKeyPath]
                         completed:
                             ^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                                 @strongify(self);
                                 if (!error) {
                                     [self theme_setBackgroundImage:nil forState:UIControlStateNormal];
                                 }
                             }];

[self theme_setBackgroundImage:nil forState:UIControlStateNormal];