writeToFile失败，错误= null

Question

我有一个应用程序在XCode模拟器（v6.4）中运行;这是相关代码：

  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]; 

我试图通过采取文件，压缩它，然后写出来，以创建一个文件的备份。我收到一个错误无法存储。错误：（null））;为什么它没有返回错误代码失败？

Answer 1

这里有很多错误。开始。改变你的if声明：

if (success) { 

从未明确一个BOOL值与YES或NO。

你也从来没有使用outputFile所以删除该代码。它可能会干扰writeToFile:的呼叫。

使用文件句柄读取数据没有意义。只需使用NSData dataWithContentsOfFile:即可。

而且不要使用stringWithFormat:构建路径。

总体来说，我会写你的代码为：

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仍然NO和error仍然nil，那么最有可能的，这意味着compressedData是nil。这可能意味着databuffer是nil，这意味着Documents文件夹中没有名为Backup.txt（案件事项）的文件。