UIDocument loadFromContents应该返回NSFileWrapper；而返回NSConcreteData

Question

我正在制作一个文本编辑器应用程序，它将其每个文档存储为一个NSFileWrapper目录，其中文档文本和文档标题作为目录中的单独文件。我希望loadFromContents: (id) contents的loadFromContents: (id) contents部分是一个NSFileWrapper，但事实并非如此。我的代码如下(它属于UIDocument的一个子类)：

// loads document data to application data model

- (BOOL) loadFromContents:(id)contents ofType:(NSString *)typeName error:(NSError *__autoreleasing *)outError {
    // from the contents, extract it so that we have the properties initialized
    self.fileWrapper = (NSFileWrapper *) contents;
    NSLog(@"%@", [contents class]); //** returns NSConcreteData

    // get the fileWrapper's children
    NSDictionary *contentsOfFileWrapper = [contents fileWrappers];

    // assign things to the document!
    // can also be done lazily through getters

    self.text = [contentsOfFileWrapper objectForKey:TEXT_KEY];
    self.title = [contentsOfFileWrapper objectForKey:TITLE_KEY];
    if ([self.delegate respondsToSelector:@selector(noteDocumentContentsUpdated:)]){
        [self.delegate noteDocumentContentsUpdated:self];
    }
    return YES;
}

当我试图调用此方法时，会得到以下错误：

*由于“NSInvalidArgumentException”异常终止应用程序，原因：'-NSConcreteData fileWrappers:未识别的选择器发送到实例0x9367150‘

下面是我的contentsForType:函数，如果它有帮助的话：

- (id) contentsForType:(NSString *)typeName error:(NSError *__autoreleasing *)outError {
    if (!self.fileWrapper) {
        self.fileWrapper = [[NSFileWrapper alloc] initDirectoryWithFileWrappers:nil];
    }

    NSDictionary *childrenFileWrappers = [self.fileWrapper fileWrappers];

    // now if we have a text but it is not represented, in the file wrapper, put it in. Same with the images.
    if ([childrenFileWrappers objectForKey:TEXT_KEY] == nil && self.text != nil) {
        NSData *textData = [self.text dataUsingEncoding:kCFStringEncodingUTF16];
        NSFileWrapper *textFileWrapper = [[NSFileWrapper alloc] initRegularFileWithContents:textData];
        [textFileWrapper setPreferredFilename:TEXT_KEY];
        [self.fileWrapper addFileWrapper:textFileWrapper];
    }

    if ([childrenFileWrappers objectForKey:TITLE_KEY] == nil && self.title != nil) {
        NSData *titleData = [self.title dataUsingEncoding:kCFStringEncodingUTF16];
        NSFileWrapper *titleFileWrapper = [[NSFileWrapper alloc] initRegularFileWithContents:titleData];
        [titleFileWrapper setPreferredFilename:TITLE_KEY];
        [self.fileWrapper addFileWrapper:titleFileWrapper];
    }

    return self.fileWrapper;

}

谢谢!

Answer 1

我解决了问题。我的Documents文件夹中有一个.DS_Store文件，它破坏了结果。有一次，我添加了一个if语句来排除它，一切正常。