Question

我正在使用Page开始新的Activator.CreateInstance

private void OnMenuSelected(object sender, SelectedItemChangedEventArgs e)
{
    if (item.Title == "Movies")
    {
        //Type page = (MasterPageItem)e.SelectedItem.TargetType; 
        //page is HomePage           
        Detail = new NavigationPage((Page)Activator.CreateInstance(page));
    }
}

HomePage.xaml.cs

public partial class HomePage : TabbedPage
{
    public string MenuName { get; set; }
    public HomePage()
    {
        InitializeComponent();
        //if (MenuName == "Movies")
        //this.CurrentPage = Children[1];
    }
}

我想从Activator.CreateInstance到MenuName发送数据，我该怎么做？由于this问题，我无法使用constructor。

Answer 1

为什么在实例化HomePage之后不能只设置MenuName属性（它是公共的）？例如：

private void OnMenuSelected(object sender, SelectedItemChangedEventArgs e)
{
    if (item.Title == "Movies")
    {
        Type page = (MasterPageItem)e.SelectedItem.TargetType; 
        //page is HomePage  
        var pageInstance = (HomePage)Activator.CreateInstance(page)
        pageInstance.MenuName = item.Title;
        Detail = new NavigationPage(pageInstance);
    }
}

如果那行不通，请解释原因？

编辑（在获得测试项目之后）：

创建HomePage实例后，您要设置MenuName：

if (item.Title == "Movies")
{               
    Type page = item.TargetType;
    var pageInstance = (HomePage)Activator.CreateInstance(page);
    // So now you already have your HomePage and you already checked 
    // in HomePage constructor for the value of MenuName, but it has
    // not been set yet, as it is set on the next line:
    pageInstance.MenuName = item.Title;
    Detail = new NavigationPage(pageInstance);
    IsPresented = false;
}

但要在HomePage构造函数中检查MenuName的值，即在设置菜单名称之前：

public HomePage()
{
    InitializeComponent();         
    if (MenuName == "Movies")
    {
        this.CurrentPage = Children[1];
    }
}

也许可以在OnAppearing替代项中检查MenuName：

public partial class HomePage : TabbedPage
{
    public string MenuName { get; set; }
    public HomePage()
    {
        InitializeComponent();         
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();
        if (MenuName == "Movies")
        {
            this.CurrentPage = Children[1];
        }
    }
}

以上似乎按预期工作。

Answer 2

我建议使用虚拟方法Initialize()创建从TabbedPage插入的基础页面

public class MyTabbedPage : TabbedPage
{
    public virtual void Initialize(object parameters)
    {

    }
}

然后您可以使用：

 private void OnMenuSelected(object sender, SelectedItemChangedEventArgs e)
        {

            //Type page = (MasterPageItem)e.SelectedItem.TargetType; 
            //page is HomePage           
            var page = (Page) Activator.CreateInstance(page);
            Detail = new NavigationPage(page);
            if (page is MyTabbedPage tabbedPage)
                tabbedPage.Initialize(params);
        }

public partial class HomePage : MyTabbedPage
    {
        public string MenuName { get; set; }
        public HomePage()
        {
            InitializeComponent();
            //if (MenuName == "Movies")
            //this.CurrentPage = Children[1];
        }

        public override void Initialize(object parameters)
        {
            //Stuff
        }
    }

也将XAML端也更改为MyTabbedPage

Answer 3

编辑：也许不是最好的主意...

使用Activator.CreateInstance。您可以执行以下操作：

private void OnMenuSelected(object sender, CustomArgstype args)
{
    var parameter = args.MenuName;
    if (parameter != null)
    {
        page = (Page)Activator.CreateInstance(type, parameter);
    }
    else
    {
        page = (Page)Activator.CreateInstance(type);
    }
}

使用Activator.CreateInstance将数据传递到其他页面

3 个答案: