Question

我也是UWP和c ++的新手。我正在尝试编写一个处理http-api的简单应用程序。我的例子：

void ForecastFromMSW::MainPage::GetTheCity(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
    String ^mystr = "http://google.com"; // creating a string object 
    Uri url(mystr); // crating an url object
    HttpClient cli; //creating an object of HttpClient
    cli.GetAsync(url); // pass url object to cli
}

来自编译器的消息：

1>------ Build started: Project: ForecastFromMSW, Configuration: Debug Win32 ------
1>  MainPage.xaml.cpp
1>c:\users\9maf4you\documents\visual studio 2015\projects\forecastfrommsw\forecastfrommsw\mainpage.xaml.cpp(38): error C2664: 'Windows::Foundation::IAsyncOperationWithProgress<Windows::Web::Http::HttpResponseMessage ^,Windows::Web::Http::HttpProgress> ^Windows::Web::Http::HttpClient::GetAsync(Windows::Foundation::Uri ^,Windows::Web::Http::HttpCompletionOption)': cannot convert argument 1 from 'Windows::Foundation::Uri' to 'Windows::Foundation::Uri ^'
1>  c:\users\9maf4you\documents\visual studio 2015\projects\forecastfrommsw\forecastfrommsw\mainpage.xaml.cpp(38): note: No user-defined-conversion operator available, or
1>  c:\users\9maf4you\documents\visual studio 2015\projects\forecastfrommsw\forecastfrommsw\mainpage.xaml.cpp(38): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
========== Deploy: 0 succeeded, 0 failed, 0 skipped ==========

我知道，编译器无法将一种类型转换为另一种类型，我知道我必须将^ Uri传递给GetAsync。但我不知道该怎么做。日Thnx。

Answer 1

在C ++ / CX中，通常使用ref new实例化对象，返回一个引用计数的对象句柄。修复代码的最简单方法是替换

Uri url(mystr);

与

Uri^ url = ref new Uri(mystr);

当编译器超出范围时，编译器将生成代码以减少url上的引用计数。当引用计数达到零时，该对象将自动销毁。

Answer 2

编译器告诉你问题

无法转换来自＆＃39; Windows :: Foundation :: Uri＆＃39;到＆＃39; Windows :: Foundation :: Uri ^＆＃39;

修复方法是使用＃34;的托管＆＃34;地址;运算符%，cli.GetAsync(%url);。您可以通过一个非常简单的测试程序看到同样的问题：

ref class Foo sealed {};
void f(Foo^) {}

int main(array<System::String ^> ^args)
{
    Foo foo;
    f(%foo);
    return 0;
}

请注意，由于您正在调用*Async()方法，因此您可能需要认真考虑使用C＃。

^ Uri to GetAsync

2 个答案: