NSMutableArray 转 json

NSMutableArray *arr = [[NSMutableArray alloc] init];

NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:
@"ni hao", @"key",
@"45", @"value",
@"USD", @"code",nil];

NSDictionary *params2 = [NSDictionary dictionaryWithObjectsAndKeys:
@"hao", @"key",
@"45", @"value",
@"USD", @"code",nil];

[arr addObject:params];
[arr addObject:params2];

NSDictionary *params3 = [NSDictionary dictionaryWithObjectsAndKeys:
arr, @"json",
nil];

//convert object to data
NSData* jsonData =[NSJSONSerialization dataWithJSONObject:params3
options:NSJSONWritingPrettyPrinted error:&error];

//print out the data contents
NSString* text =[[NSString alloc] initWithData:jsonData
encoding:NSUTF8StringEncoding];

NSLog(@"json字典里面的内容为--》%@", text );