如何从Xamarin表单的主从页面中传递字符串数据

Question

I am trying to make a Master-Detail Navigation using help of this github example. The relevant code sample from my project is -

MasterPageItem.cs

namespace Demo.MenuItems
{
    public class MasterPageItem
    {
        public string Title { get; set; }

        public string IconSource { get; set; }

        public Type TargetType { get; set; }
    }
}

MainPage.Xaml.cs

public partial class MainPage : MasterDetailPage
    {
        public MainPage()
        {
            InitializeComponent();

            masterPage.ListView.ItemSelected += OnItemSelected;

            if (Device.RuntimePlatform == Device.UWP)
            {
                MasterBehavior = MasterBehavior.Popover;
            }

            Detail = new NavigationPage(new HomePage());
        }

        void OnItemSelected(object sender, SelectedItemChangedEventArgs e)
        {
            var item = e.SelectedItem as MasterPageItem;
            if (item != null)
            {
                Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType));
                masterPage.ListView.SelectedItem = null;
                IsPresented = false;
            }
        }
    }

MasterPage.Xaml.cs

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class MasterPage : ContentPage
{
    public ListView ListView { get { return listView; } }

    public MasterPage()
    {
        InitializeComponent();

        var masterPageItems = new List<MasterPageItem>();

        masterPageItems.Add(new MasterPageItem
        {
            Title = "Help",
            IconSource = "icon-1.jpg",
            TargetType = typeof(WebPage)
        });
        listView.ItemsSource = masterPageItems;
    }
}

It works if no data is required to pass in detail page. However, I need to pass one string value url in page WebPage , but I am unable to figure out how to pass string value or any data in following line -

Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType));

For eg, following is the code sample for the page WebPage -

public WebPage (string URL)
{
    InitializeComponent ();
    Browser.Source = URL;
}

Here I am unable to figure out, how should I pass url from Master-Detail Navigation?

Answer 1

Generalized Way :

//This will create instance of the page using the parameterized constructor you defined in each DetailPages
Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType, myStringParam));


//Your Each Detail Page should have parametrized constructor.
public MyPage (string param)
{
    InitializeComponent ();
    Browser.Source = param;
}

Here, you can serialize the c# object and pass JSON string into myStringParam. Your page receives this in page's parameterized constructor you defined and there, you can deserialize, thus you can pass complex objects as JSON into a page as well as simple string.

If you want to add parameterized constructor in only one DetailPage then :

if(item.TargetType == typeof(WebPage))
{
    Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType, myStringParam));
}
else
{
    Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType));
}

//Your Page would be:
public WebPage (string URL)
{
    InitializeComponent ();
    Browser.Source = URL;
}

Answer 2

Yes you can Activator.CreateInstance Method as many overloads

Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType, url));

All the overloads can be found here

Activator.CreateInstance Method

The one you want is here

Activator.CreateInstance Method (Type, Object[])

Parameters

type Type: System.Type

The type of object to create

args Type: System.Object[]

An array of arguments that match in number, order, and type the parameters of the constructor to invoke. If args is an empty array or null, the constructor that takes no parameters (the default constructor) is invoke