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  • Read and Write NSArray, NSDictionary and NSSet to a File

    查询地址:http://iosdevelopertips.com/data-file-management/read-and-write-nsarray-nsdictionary-and-nsset-to-a-file.html

    With just a few lines of code, you can read/write collections to/from files. The code below shows examples for writing and reading both NSArray and NSDictionary objects, the same logic would apply to an NSSet (or other collection type).

    The example below starts by populating both an array and dictionary, each using the Objective-C literal syntax. Read more about using NSArray literals andNSDictionary literals.

    Read and Write Collections to File

    The process is straightforward:

    – Create the NSArray and NSDictionary objects
    – Obtain the path to write/read the files (application Documents directory)
    – Append filenames to path for each collection type
    – Use the ‘writeToFile:’ method of each object to save contents to file

    NSString  *arrayPath;
    NSString  *dictPath;
    NSArray *array = @[@"IPA", @"Pilsner", @"Stout"];
     
    NSDictionary *dictionary = @{@"key1" : array,
                                 @"key2" : @"Hops",
                                 @"key3" : @"Malt",
                                 @"key4" : @"Yeast" };
     
    // Get path to documents directory
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, 
      NSUserDomainMask, YES);
     
    if ([paths count] > 0)
    {
      // Path to save array data
      arrayPath = [[paths objectAtIndex:0] 
          stringByAppendingPathComponent:@"array.out"];
     
      // Path to save dictionary
      dictPath = [[paths objectAtIndex:0] 
          stringByAppendingPathComponent:@"dict.out"];
     
      // Write array
      [array writeToFile:arrayPath atomically:YES];
     
      // Write dictionary
      [dictionary writeToFile:dictPath atomically:YES];
    }

    Read NSArray NSDictionary NSSet From File

    The code to read back from the collections is equally as simple, using the methods arrayWithContentsOfFile: and dictionaryWithContentsOfFile: read from the file paths created previously to read the save data:

    // Read both back into new NSArray and NSDictionary object
    NSArray *arrayFromFile = [NSArray arrayWithContentsOfFile:arrayPath];
    NSDictionary *dictFromFile = [NSDictionary dictionaryWithContentsOfFile:dictPath];
     
    // Print the contents
    for (NSString *element in arrayFromFile) 
      NSLog(@"Beer: %@", element);
     
    for (NSString *key in dictFromFile) 
      NSLog(@"%@ : %@", key, [dictionary valueForKey:key]);

    The output in the console window is below:

    Beer: IPA
    Beer: Pilsner
    Beer: Stout
    key1 : (
        IPA,
        Pilsner,
        Stout
    )
    key2 : Hops
    key3 : Malt
    key4 : Yeast
    如果一件事情你觉得难的完不成,你可以把它分为若干步,并不断寻找合适的方法。最后你发现你会是个超人。不要给自己找麻烦,但遇到麻烦绝不怕,更不要退缩。 电工查找电路不通点的最快方法是:分段诊断排除,快速定位。你有什么启示吗? 求知若饥,虚心若愚。 当你对一个事情掌控不足的时候,你需要做的就是“梳理”,并制定相应的规章制度,并使资源各司其职。
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  • 原文地址:https://www.cnblogs.com/wvqusrtg/p/4548239.html
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