{
"info":{
"type":34,
"error":0
},
"poilist":[
{
"x":116.345,
"name":"银科大厦",
"y":39.333399999999997
},
{
"x":116.3451,
"name":"中国技术交易大厦",
"y":39.313339999999997
}
]
}

NSDictionary* jsonDic = [[NSMutableDictionary alloc] init];
//添加info字段
NSDictionary* jsonInfoDic = [[NSMutableDictionary alloc] init];
[jsonInfoDic setValue:[NSNumber numberWithInteger:0] forKey:@"error"];
[jsonInfoDic setValue:[NSNumber numberWithInteger:34] forKey:@"type"];
[jsonDic setValue:jsonInfoDic forKey:@"info"];
[jsonInfoDic release];

//添加poilist字段
NSDictionary* poi1 = [NSDictionary dictionaryWithObjectsAndKeys:
                      @"银科大厦",@"name",
                      [NSNumber numberWithDouble:116.345],@"x",
                      [NSNumber numberWithDouble:39.3334],@"y",
                      nil];

NSDictionary* poi2 = [NSDictionary dictionaryWithObjectsAndKeys:
                      @"中国技术交易大厦",@"name",
                      [NSNumber numberWithDouble:116.3451],@"x",
                      [NSNumber numberWithDouble:39.31334],@"y",
                      nil];
NSArray* jsonPoiList = [NSArray arrayWithObjects:poi1,poi2, nil];
[jsonDic setValue:jsonPoiList forKey:@"poilist"];

NSString* string = [jsonDic JSONString];

NSLog(@"jsonString=%@",string);
[jsonDic release];

NSString* jsonString =   @"{\"info\":{\"error\":0,\"type\":34},\"poilist\":[{\"name\":\"银科大厦\",\"x\":116.345,\"y\":39.3334},{\"name\":\"中国技术交易大厦\",\"x\":116.3451,\"y\":39.31334}]}";

    id root = [jsonString objectFromJSONString];

    if ([root isKindOfClass:[NSDictionary class]]) {

        id jsonInfo = [root objectForKey:@"info"];

        if ([jsonInfo isKindOfClass:[NSDictionary class]]) {
            NSInteger error = [[jsonInfo objectForKey:@"error"] intValue];
            NSInteger type = [[jsonInfo objectForKey:@"type"] intValue];

            NSLog(@"error = %d,type = %d",error,type);
        }

        id jsonPoiList = [root objectForKey:@"poilist"];

        if ([jsonPoiList isKindOfClass:[NSArray class]]) {
            NSArray* jsonPoiArray = (NSArray*)jsonPoiList;

            for (id jsonPoiDic in jsonPoiArray) {

                if ([jsonPoiDic isKindOfClass:[NSDictionary class]]) {
                    NSString* name = [jsonPoiDic objectForKey:@"name"];
                    double x = [[jsonPoiDic objectForKey:@"x"] doubleValue];
                    double y = [[jsonPoiDic objectForKey:@"y"] doubleValue];

                    NSLog(@"poi:{name=%@,x=%f,y=%f}",name,x,y);

                }
            }
        }
    }