如何声明对象的属性?[关闭]

我在xcode中得到这个错误:

在“xcuidevice”类型的对象上找不到属性“fb_screenshot”

我该怎么申报?

以下是我的部分代码:

+ (id<FBResponsePayload>)handleGetScreenshot:(FBRouteRequest *)request
{
    [UtilsLogger logMessage:[NSString stringWithFormat:@"Handling : %@", request.URL.absoluteURL] sender:METHOD_NAME];
    @try {
        NSString *screenshot = [[XCUIDevice sharedDevice].fb_screenshot base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
        return [Response withSucessString:screenshot methodName:METHOD_NAME logString:false] ;
    }
    @catch (NSException *exception) {
        return [Response withException:exception methodName:METHOD_NAME];
    }
}