NSFileHandle fileHandleForWritingAtPath:返回null！

Question

我的iPad应用程序有一个小的下载工具，我想要使用NSFileHandle附加数据。问题是创建调用只返回空文件句柄。可能的问题是什么？下面是创建我的文件句柄的三行代码：

NSString *applicationDocumentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
self.finalPath = [applicationDocumentsDirectory stringByAppendingPathComponent: self.fileName]; 
NSFileHandle *output = [NSFileHandle fileHandleForWritingAtPath:self.finalPath];

我检查了文件路径，没有发现任何问题。

TYIA

Answer 1

fileHandleForWritingAtPath不是一个“创建”调用。文档明确声明：“返回值:已初始化的文件句柄，如果路径处不存在文件，则返回nil”(强调添加)。如果您希望在文件不存在的情况下创建该文件，则必须使用以下内容：

 NSFileHandle *output = [NSFileHandle fileHandleForWritingAtPath:self.finalPath];
 if(output == nil) {
      [[NSFileManager defaultManager] createFileAtPath:self.finalPath contents:nil attributes:nil];
      output = [NSFileHandle fileHandleForWritingAtPath:self.finalPath];
 }

如果你想附加到文件，如果它已经存在，使用类似[output seekToEndOfFile]的东西。然后，您的完整代码将如下所示：

 NSString *applicationDocumentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
 self.finalPath = [applicationDocumentsDirectory stringByAppendingPathComponent: self.fileName]; 
 NSFileHandle *output = [NSFileHandle fileHandleForWritingAtPath:self.finalPath];
 if(output == nil) {
      [[NSFileManager defaultManager] createFileAtPath:self.finalPath contents:nil attributes:nil];
      output = [NSFileHandle fileHandleForWritingAtPath:self.finalPath];
 } else {
      [output seekToEndOfFile];
 }

Answer 2

获取文档目录路径

+(NSURL *)getDocumentsDirectoryPath
{
    return [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask]lastObject];
}

将文本保存到文件的末尾

如果文件不存在，则创建它并写入数据

+(void)saveText:(NSString *)textTobeSaved atPath:(NSString*)fileName
{
    NSString *filePath = [NSString stringWithFormat:@"%@.text",fileName];
    
    NSString *path = [[self getDocumentsDirectoryPath].path
                      stringByAppendingPathComponent:filePath];
    NSFileHandle *fileHandler = [NSFileHandle fileHandleForWritingAtPath:path];
    if(fileHandler == nil) {
        [[NSFileManager defaultManager] createFileAtPath:path contents:nil attributes:nil];
        fileHandler = [NSFileHandle fileHandleForWritingAtPath:path];
    } else {
        textTobeSaved = [NSString stringWithFormat:@"\n-----------------------\n %@",textTobeSaved];
        [fileHandler seekToEndOfFile];
    }
    
    [fileHandler writeData:[textTobeSaved dataUsingEncoding:NSUTF8StringEncoding]];
    [fileHandler closeFile];
}

从具有指定文件名的文件获取文本

+(NSString *)getTextFromFilePath:(NSString *)fileName
{
    NSString *filePath = [NSString stringWithFormat:@"%@.text",fileName];
    
    NSString *path = [[self getDocumentsDirectoryPath].path
                      stringByAppendingPathComponent:filePath];
    NSLog(@"%@",path);
    if(path!=nil)
    {
    NSString *savedString = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];
    
    return savedString;
  }else{
    return @"";
  } 
}

删除文件

+(void)deleteFile:(NSString *)fileName
{
    NSString *filePath = [NSString stringWithFormat:@"%@.text",fileName];
    
    NSString *path = [[self getDocumentsDirectoryPath].path
                      stringByAppendingPathComponent:filePath];
    
    NSFileHandle *fileHandler = [NSFileHandle fileHandleForWritingAtPath:path];
    if(fileHandler != nil) {
        [[NSFileManager defaultManager]removeItemAtPath:path error:nil];
    }
    
}