writeToFile失敗，錯誤= null

Question

我有一個應用程序在XCode模擬器（v6.4）中運行;這是相關代碼：

  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]; 

我試圖通過採取文件，壓縮它，然後寫出來，以創建一個文件的備份。我收到一個錯誤無法存儲。錯誤：（null））;爲什麼它沒有返回錯誤代碼失敗？

Answer 1

這裏有很多錯誤。開始。改變你的if聲明：

if (success) { 

從未明確一個BOOL值與YES或NO。

你也從來沒有使用outputFile所以刪除該代碼。它可能會干擾writeToFile:的呼叫。

使用文件句柄讀取數據沒有意義。只需使用NSData dataWithContentsOfFile:即可。

而且不要使用stringWithFormat:構建路徑。

總體來說，我會寫你的代碼爲：

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); 
} 

由於success仍然NO和error仍然nil，那麼最有可能的，這意味着compressedData是nil。這可能意味着databuffer是nil，這意味着Documents文件夾中沒有名爲Backup.txt（案件事項）的文件。