Question

我有一份现有文件,我希望删除其内容,然后再次写到,但只是按行文读。我的守则不能确定为什么不工作:

if ([filemgr removeItemAtPath: fileName error: NULL]  == YES){
        NSLog (@"Remove successful");
    }
    else{
        NSLog (@"Remove failed");
    }

    NSString *cachePath = [[NSString alloc] initWithFormat:@"%@",fileName];
    NSFileHandle *fileHandler = [NSFileHandle fileHandleForUpdatingAtPath:cachePath];
    BOOL isFirst = NO;

    for(id entry in serializedObjects){
        NSString *sectionName = [NSString stringWithFormat:@"!%@
", entry];
        [fileHandler writeData:[sectionName dataUsingEncoding:NSUTF8StringEncoding]];

        if (!isFirst) {
            [fileHandler seekToEndOfFile];
            isFirst = YES;
        }

        NSArray *list = [serializedObjects objectForKey:entry];

        for (int i = 0; i < list.count; i++) {
            NSString *line = [[list objectAtIndex:i] stringByAppendingString:@"
"];
            [fileHandler writeData:[line dataUsingEncoding:NSUTF8StringEncoding]];
        }

        [fileHandler writeData:[[NSString stringWithFormat:@"%@", @"~
"] dataUsingEncoding:NSUTF8StringEncoding]];
    }

[fileHandler closeFile];

我的想法是把第一行写到档案中,并对他人进行传阅。是否有任何人看到我在这里做错?

在这种方法完成后,我看不到任何错误,但Im试图写上字面的文件在我进行人工检查后就存在。

Answer 1

Your file handle writes to the I/O buffer which will not instantly write to disk. Because io is slow this is efficiency built into file handle objects. To ensure it writes to disk you must flush the io buffer using synchronizeFile. You also need to call closeFile when you are done with the file handle (which will also synchronize, so the synchronize is optional).

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