ObjectiveC：如何向 NSURL 添加查询参数

假设我有一个NSURL？无论它是否已经有一个空的查询字符串，我如何向NSURL中的query添加一个或多个参数？也就是说，有人知道该功能的实现吗？

- (NSURL *)URLByAppendingQueryString:(NSString *)queryString

所以它满足这个NSURL+AdditionsSpec.h文件:

#import "NSURL+Additions.h"
#import "Kiwi.h"

SPEC_BEGIN(NSURL_AdditionsSpec)

describe(@"NSURL+Additions", ^{
    __block NSURL *aURL;

    beforeEach(^{
        aURL = [[NSURL alloc] initWithString:@"http://www.example.com"];
        aURLWithQuery = [[NSURL alloc] initWithString:@"http://www.example.com?key=value"];
    });

    afterEach(^{
        [aURL release];
        [aURLWithQuery release];
    });

    describe(@"-URLByAppendingQueryString:", ^{
        it(@"adds to plain URL", ^{
            [[[[aURL URLByAppendingQueryString:@"key=value&key2=value2"] query] should]
             equal:@"key=value&key2=value2"];
        });

        it(@"appends to the existing query sting", ^{
            [[[[aURLWithQuery URLByAppendingQueryString:@"key2=value2&key3=value3"] query] should]
             equal:@"key=value&key2=value2&key3=value3"];
        });
    });
});

SPEC_END