Objective-C 文件 I/O 错误

Question

- (IBAction)sendMessage:(id)sender
{
    NSString* conversationFile = [@"~/" stringByAppendingPathComponent:@"conversation.txt"];
    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:conversationFile];

    if (fileExists == FALSE)
    {
        [self doShellScript:@"do shell script \"cd ~/; touch conversation.txt\""];
    }

    NSString *conversationContent = [[NSString alloc] stringWithContentsOfFile:@"~/conversation.txt" encoding:NSUTF8StringEncoding error:NULL];
    NSString *myMessage = [[messageBox stringValue]copy];

    NSString *combinedContent = [NSString stringWithFormat:@"%@ \r\n %@", conversationContent, myMessage];
    [[[myConversationBox textStorage] mutableString] setString: combinedContent];
    [combinedContent writeToFile:@"~/conversation.txt" atomically:YES encoding:NSUTF8StringEncoding error:NULL];

}

上面的代码出现以下错误

2011-07-07 21:38:08.703 iMessages[86493:903] -[NSPlaceholderString stringWithContentsOfFile:编码:错误:]: 无法识别的选择器发送到实例 0x100111690

2011-07-07 21:38:08.704 iMessages[86493:903] -[NSPlaceholderString stringWithContentsOfFile:编码:错误:]: 无法识别的选择器发送到实例 0x100111690

Answer 1

stringWithContentsOfFile:encoding:error: 是 NSString 的类方法，而不是实例方法，因此您不需要（不应该）先分配它。

NSString *conversationContent = [NSString stringWithContentsOfFile:@"~/conversation.txt" encoding:NSUTF8StringEncoding error:NULL];

Answer 2

使用 initWithContentsOfFile 代替 stringWithContentsOfFile 或删除 alloc 调用。所以有：

NSString *conversationContent = [[NSString alloc] initWithContentsOfFile:@"~/conversation.txt" encoding:NSUTF8StringEncoding error:NULL];

或

NSString *conversationContent = [NSString stringWithContentsOfFile:@"~/conversation.txt" encoding:NSUTF8StringEncoding error:NULL];