writeToFile 没有写入文件

Posted 2023-03-07

【中文标题】writeToFile 没有写入文件

【英文标题】：writeToFile is not writing to the file

【发布时间】：2011-10-03 13:31:44

【问题描述】：

嗯，我遇到了一个问题，我已经为此苦苦挣扎了几天。这里是：当尝试使用 writeToFile 写入 xml 文件（放置在我正在开发的 xcode 项目中）时，写入不起作用，我在 xml 文件中什么也看不到，尽管从 writeToFile 返回的布尔值是被评价为真！！此外，文件字节为零。所以，如果有人能帮我解决这个问题，我将不胜感激。以下是我写的部分代码：

//writing to a file
 NSString *pathOfFile = [[NSBundle mainBundle] pathForResource:@"sample" ofType:@"xml"];
 NSString *dummyString = @"Hello World!!\n"; 
 NSFileManager *filemanager;

 filemanager = [NSFileManager defaultManager];

  //entering the first condition so I assured that the file do exists
  if ([filemanager fileExistsAtPath:pathOfFile] == YES)
     NSLog (@"File do exist !!!");
   else
     NSLog (@"File not found !!!");


BOOL writingStatus = [dummyString writeToFile:path atomically:YES encoding:NSUnicodeStringEncoding error:nil];

    //Not entering this condition so I am assuming that writing process is successful but when I open the file I can't find the string hello world and file size shows 0 bytes
    if(!writingStatus)
    
        NSLog(@"Error: Could not write to the file");
    

我也尝试过这种替代方法，但不幸的是它也不起作用。

NSString *hello_world = @"Hello World!!\n";
NSArray  *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *directory = [paths objectAtIndex:0];
NSString *fileName = @"sample.xml";
NSString *filePath = [directory stringByAppendingPathComponent:fileName];
NSLog(@"%@",filePath);
BOOL sucess = [hello_world writeToFile:filePath atomically:YES encoding:NSASCIIStringEncoding error:nil];  
if(!sucess)

    NSLog(@"Could not to write to the file");

【问题讨论】：

我们在这里讨论的是 ios 还是 MacOS X？请标记您的问题以表明这一点。

【参考方案1】：

在第一段代码中，我们看不到path的定义。如果这是一个错字并且您的意思是file_path，那么问题是file_path 指向应用程序包内的路径。你不能在你的应用程序包内写。 （不应该有任何拼写错误，因为您应该直接粘贴代码。）

在第二种情况下，很难说出问题所在。 filePath 应该在可写的文档目录中。但是，如果您遇到实际错误，诊断问题会容易得多。不要为-writeToFile:atomically:encoding:error: 中的错误参数传递nil，而是创建一个NSError* 变量并传入其地址。如果有问题，那么，您的指针将被设置为指向描述问题的 NSError 对象。

【讨论】：

是的，我的意思是文件路径而不是第一部分代码中的路径。这是一个错字，因为我试图定义另一条路径，然后我忘记了改变它。关于第二段代码，我将添加一个错误变量来进一步诊断问题。感谢您提供的宝贵信息，它真的很有帮助。那么，没有蚂蚁的方式我们可以写入 ye App bundle 中的文件吗？

@User897，不，你是mustn't write to your app bundle。即使您能找到这样做的方法，您的数据也不会在用户同步时备份，并且您会使允许应用运行的签名无效。

【参考方案2】：

writeToFile: 返回布尔值 YES 的事实仅仅意味着调用正在完成。

您应该将NSError** 传递给writeToFile: 并检查它，例如：

 NSError *error = nil;
 BOOL ok = [hello_world writeToFile:filePath atomically:YES 
                        encoding:NSASCIIStringEncoding error:&error];
 if (error) 
      NSLog(@"Fail: %@", [error localizedDescription]);
 

这应该可以让您很好地了解发生了什么问题（假设错误在调用后不为零）。

【参考方案3】：

-(void)test
//writing to a file
    NSError *error;
    NSString *pathOfFile = [[NSBundle mainBundle] pathForResource:@"sample" ofType:@".xml"];//was missing '.'
NSString *dummyString = @"Hello World!!\n";
NSFileManager *filemanager;

filemanager = [NSFileManager defaultManager];

//entering the first condition so I assured that the file do exists
   //the file exists in the bundle where you cannot edit it

    if ([filemanager fileExistsAtPath:pathOfFile])
        NSLog (@"File do exist IN Bundle MUST be copied to editable location!!!");
        NSArray *locs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *docsDir = [[locs objectAtIndex:0]stringByAppendingString:@"dummyFile"];
        NSString *file = [docsDir stringByAppendingPathComponent:@".xml"];

        [filemanager copyItemAtPath:pathOfFile toPath:file error:&error];
    
    else
NSLog (@"File not found in bundle!!!");

    

    if (error) 
        NSLog(@"error somewhere");
    


//if youre only messing with strings you might be better off using .plist file idk
BOOL success = [dummyString writeToFile:file atomically:YES encoding:NSUnicodeStringEncoding error:nil];

//Not entering this condition so I am assuming that writing process is successful but when I open the file I can't find the string hello world and file size shows 0 bytes
if(!success)

    NSLog(@"Error: Could not write to the file");

【参考方案4】：

//I typically do something like this

//lazy instantiate a property I want such as array.
-(NSMutableArray*)array
    if (!_array) 
        _array = [[NSMutableArray alloc]initWithContentsOfFile:self.savePath];
    
    return _array;


//I'm using a class to access anything in the array from as a property from any other class
//without using NSUserDefaults.

//initializing the class
-(instancetype)init

    self = [super init];
    if (self) 
    //creating an instance of NSError for error handling if need be.
        NSError *error;
    //build an array of locations using the NSSearchPath...  
        NSArray *locs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,     NSUserDomainMask, YES);
        //location 0 of array is Documents Directory which is where I want to create    the file
        NSString *docsDir = [locs objectAtIndex:0];
//my path is now just a matter of adding the file name to the docsDir
        NSString *path = [docsDir stringByAppendingPathComponent:@"fileName.plist"];
//if the file is a plist I have in my bundle I need to copy it to the docsDir to edit it

//I'll do that by getting it from the bundle that xCode made for me
        NSString *bunPath = [[NSBundle mainBundle]pathForResource:@"fileName"     ofType:@".plist"];


//now I need a NSFileManager to handle the dirty work
        NSFileManager *filemngr = [NSFileManager defaultManager];


//if the file isn't in my docsDir I can't edit so I check and if need be copy it.        
        if (![filemngr fileExistsAtPath:path]) 
            [filemngr copyItemAtPath:bunPath toPath:path error:&error];

//if an error occurs I might want to do something about it or just log it as in below.
//I believe you can set error to nil above also if you have no intentions of dealing with it.
            if (error) 
                NSLog(@"%@",[error description]);
                error = nil;

            
//here I'm logging the paths just so you can see in the console what's going on while     building or debugging.
            NSLog(@"copied file from %@ to %@",bunPath,path);
        

//in this case I'm assigning the array at the root of my plist for easy access
        _array = [[NSMutableArray alloc]initWithContentsOfFile:path];
        _savePath = path;//this is in my public api as well for easy access.

    

    return self;