如何从MessagingCenter调用中返回值？

Question

我们在项目中使用Xamarin.Forms，并订阅了对DisplayAlert和DisplayActionSheet原生函数的MessagingCenter调用。

以下是我们在视图中订阅它的方式：

MessagingCenter.Subscribe<ViewModelBase, List<string>> (this, "DisplayActionSheet", (sender, values) => {
    string title = values[0];
    values.RemoveAt(0);
    DisplayActionSheet (title, "Annuler", null, values.ToArray());
});

下面是我们在ViewModel中实现它的方式

public async void DisplayActionSheet(string title, string[] actions){
    List<string> values = new List<string>(actions);
    values.Insert (0, title);
    MessagingCenter.Send<ViewModelBase, List<string>> (this, "DisplayActionSheet", values);
}

所以我们可以这样称呼它：

string[] actions = {"Charmander", "Pikachu", "Squirtle"};
DisplayActionSheet("Choose your pokemon", actions);

我们如何向消息发送者返回值？

Answer 1

您可以通过MessagingCenter传回DisplayActionSheet的结果。

例如

await result = DisplayActionSheet(....);
MessagingCenter.Send<MyPage, string> (this, "DisplayResult", result);
// Then where you need it
MessagingCenter.Subscribe<MyPage, string> (this, "DisplayResult", (sender, displayResultString) => {
    // do something with displayResultString
});