Question

我在XCode模拟器中运行了一个应用程序（v6.4）;这是相关的代码：

            NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

        //  read the file back into databuffer...
        NSFileHandle *readFile = [NSFileHandle fileHandleForReadingAtPath:[documentsPath stringByAppendingPathComponent: @"Backup.txt"]];
        NSData *databuffer = [readFile readDataToEndOfFile];
        [readFile closeFile];

        // compress the file
        NSData *compressedData = [databuffer gzippedData] ;

        // Write to disk
        NSString *outputPath = [NSString stringWithFormat:@"%@/%@%@.zip", documentsPath, venueName, strDate];
        _BackupFilename = fileName;  //  save for upload

        NSFileHandle *outputFile = [NSFileHandle fileHandleForWritingAtPath:outputPath];
        NSError *error = nil;

        //  write the data for the backup file
        BOOL success = [compressedData writeToFile: outputPath options: NSDataWritingAtomic error: &error];

        if (error == nil && success == YES) {
            NSLog(@"Success at: %@",outputPath);
        }
        else {
            NSLog(@"Failed to store. Error: %@",error);
        }

        [outputFile closeFile];

我尝试通过获取文件，压缩文件然后将其写出来创建文件的备份。我收到错误无法存储。错误：（null））;为什么没有返回错误代码就失败了？

Answer 1

这里有很多不妥之处。开始。将您的if声明更改为：

if (success) {

绝不明确将BOOL值与YES或NO进行比较。

您也永远不会使用outputFile，因此请删除该代码。它可能会干扰对writeToFile:的调用。

使用文件句柄读取数据毫无意义。只需使用NSData dataWithContentsOfFile:。

不要使用stringWithFormat:构建路径。

总的来说，我会将您的代码编写为：

NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

//  read the file back into databuffer...
NSString *dataPath = [documentsPath stringByAppendingPathComponent:@"Backup.txt"]];
NSData *databuffer = [NSData dataWithContentsOfFile:dataPath];

// compress the file
NSData *compressedData = [databuffer gzippedData];

// Write to disk
NSString *outputName = [NSString stringWithFormat:@"%@%@.zip", venueName, strDate];
NSString *outputPath = [documentsPath stringByAppendingPathComponent:outputName];

//  write the data for the backup file
NSError *error = nil;
BOOL success = [compressedData writeToFile:outputPath options:NSDataWritingAtomic error:&error];

if (success) {
    NSLog(@"Success at: %@",outputPath);
} else {
    NSLog(@"Failed to store. Error: %@",error);
}

由于success仍为NO且error仍为nil，因此很可能这意味着compressedData为nil。这可能意味着databuffer为nil，这意味着Backup.txt文件夹中没有名为Documents的文件（案例很重要）。

writeToFile失败，错误= null

1 个答案: