我们如何储存到NSDictionary中？ NSDictionary和NSMutableDictionary有什么区别？

Question

我正在开发一个应用程序，我想在其中使用NSDictionary。任何人都可以给我一个示例代码，说明如何使用NSDictionary存储数据的过程如何完美的例子？

Answer 1

NSDictionary和NSMutableDictionary文档可能是您最好的选择。他们甚至对如何做各种事情，像一些伟大的例子...

......创建一个NSDictionary

NSArray *keys = [NSArray arrayWithObjects:@"key1", @"key2", nil]; 
NSArray *objects = [NSArray arrayWithObjects:@"value1", @"value2", nil]; 
NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:objects 
                 forKeys:keys];

......遍历它

for (id key in dictionary) { 
    NSLog(@"key: %@, value: %@", key, [dictionary objectForKey:key]); 
}

...让它变为可变

NSMutableDictionary *mutableDict = [dictionary mutableCopy];

注：历史版本之前，2010：[辞典mutableCopy]自动释放]

......并改变它

[mutableDict setObject:@"value3" forKey:@"key3"];

......然后将其存储到文件

[mutableDict writeToFile:@"path/to/file" atomically:YES];

...并将其读回aga在

NSMutableDictionary *anotherDict = [NSMutableDictionary dictionaryWithContentsOfFile:@"path/to/file"];

......读值

NSString *x = [anotherDict objectForKey:@"key1"]; 

......检查是否存在关键

if ([anotherDict objectForKey:@"key999"] == nil) NSLog(@"that key is not there"); 

......使用可怕的未来语法

从2014年起，你其实可以只输入字典[@ “钥匙”]而不是[字典objectForKey：@ “钥匙”]

Answer 2

NSDictionary *dict = [NSDictionary dictionaryWithObject: @"String" forKey: @"Test"]; 
NSMutableDictionary *anotherDict = [NSMutableDictionary dictionary]; 

[anotherDict setObject: dict forKey: "sub-dictionary-key"]; 
[anotherDict setObject: @"Another String" forKey: @"another test"]; 

NSLog(@"Dictionary: %@, Mutable Dictionary: %@", dict, anotherDict); 

// now we can save these to a file 
NSString *savePath = [@"~/Documents/Saved.data" stringByExpandingTildeInPath]; 
[anotherDict writeToFile: savePath atomically: YES]; 

//and restore them 
NSMutableDictionary *restored = [NSDictionary dictionaryWithContentsOfFile: savePath]; 

Answer 3

关键的区别：的NSMutableDictionary可以就地修改的NSDictionary不能。对于Cocoa中的所有其他NSMutable *类都是如此。 NSMutableDictionary是NSDictionary的子类，所以你可以用NSDictionary做的所有事情都可以用两者来完成。但是，NSMutableDictionary还添加了补充方法来修改适当位置的内容，例如方法setObject:forKey:。

您可以在两个这样的之间的转换：

NSMutableDictionary *mutable = [[dict mutableCopy] autorelease]; 
NSDictionary *dict = [[mutable copy] autorelease]; 

大概希望将其写入文件来存储数据。NSDictionary中有一个方法来做到这一点（也可与的NSMutableDictionary）：

BOOL success = [dict writeToFile:@"/file/path" atomically:YES]; 

为了从文件中读取一个字典，有一个相应的方法：

NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:@"/file/path"]; 

如果你想阅读的文件一个NSMutableDictionary，只需使用：

NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile:@"/file/path"];