Question

我的iPad应用程序有一个小的下载工具，我想使用NSFileHandle附加数据。问题是创建调用只返回空文件句柄。可能是什么问题呢？以下是应该创建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，我没有看到任何错误。

TYIA

Answer 1

fileHandleForWritingAtPath不是“创建”电话。文档明确指出：“返回值：初始化文件句柄，如果路径中没有文件，则 nil”（强调添加）。如果您希望创建该文件（如果该文件不存在），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]; }

如果要附加到文件（如果已存在），请使用[output seekToEndOfFile]之类的内容。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];
}

将文字保存到文件末尾

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];
}

从文件获取指定文件名的文本

+(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];
    }

}

NSFileHandle fileHandleForWritingAtPath：返回null！

2 个答案: