特殊情况：结合SDWebImage使用

[zhao0]

我在实际使用中遇到这种情况

[self.avatar sd_setBackgroundImageWithURL:[NSURL URLWithString:self.avatar]
                                     forState:UIControlStateNormal
                             placeholderImage:[UIImage imageWithName:@"img_avatar_user_default"]];

要求placeholderImage根据主题不同使用不同图片，不知道有什么合适的方法

[wxxsw]

首先得到当前主题应该设置的占位图片名：

• 通过索引

// ThemeManager.currentThemeIndex 可以获得当前主题的索引
NSString *imageName = ThemeManager.currentThemeIndex == 0 ? @"first_image" : @"second_image";

• 通过plist

// stringForKeyPath可以直接获得keyPath中的值
NSString *imageName = [ThemeManager stringForKeyPath:@"YourImageNameKeyPath"];

然后设置图片：

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

上面的方法有一个缺陷，当avatar正显示占位图时切换主题，此时占位图并不会随主题改变，如果这种情况比较明显，可以注册通知ThemeUpdateNotification，触发时重新调用一次上面的步骤设置avatar

[zhao0]

其实我是想让placeholderImage也用上ThemeImagePicker，后来想了一个不是很优雅的方法

- (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];
                                     }
                                 }];
}

[wxxsw]

这个方法看上去是可行的，可以改进的是：

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

然后你可以这样写：

[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];
                                 }
                             }];

---

现在已经支持这样写（需要更新一下SwiftTheme，版本0.2.1）：

[self theme_setBackgroundImage:nil forState:UIControlStateNormal];

[zhao0]

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