37

我的 iPad 应用程序有一个小型下载工具，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？这是应该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，我看不出有什么问题。

TYIA

4

2 回答 2

88

fileHandleForWritingAtPath不是“创造”电话。文档明确指出：“返回值：初始化的文件句柄，如果路径不存在文件，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];
 }

如果要附加到文件（如果文件已存在），请使用类似[output seekToEndOfFile]. 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];
 }
于 2010-09-17T13:15:27.173 回答
0

获取文档目录路径

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

将文本保存到文件末尾

如果文件不存在创建它并写入数据

+(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中获取文本

+(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];
    }
    
}
于 2017-11-02T09:02:57.433 回答