Question

创建新堆栈并传递数据

// This code is the main page of the application.
await Navigation.PushAsync(new TodoItemPage
{
BindingContext = e.SelectedItem as Models.TodoItem,
});

数据在TodoItemPage中传输

public TodoItemPage()
{
InitializeComponent();
Title = "Name"; // here need show NAME - I can't display my name here
var nameEntry = new Entry();
nameEntry.SetBinding(Entry.TextProperty, "Name");
Content = new StackLayout
            {
                Margin = new Thickness(20),
                VerticalOptions = LayoutOptions.StartAndExpand,
                Children =
                {
                    new Label { Text = "Name" },
                    nameEntry, // here NAME is shown
                }
            };

如何从BindingContext到TodoItemPage页面上的变量获取属性的值？

VS，C＃，Xamarin形式

我尝试过

var data = (Models.TodoItem)BindingContext;
data.ID;
data.Name;

...

Answer 1

对象类的Cast BindingContext。

示例：

 public class TodoItem
{
    public int Prop1 { get; set; }
    public string Prop2 { get; set; }
}

然后使用

var data =  BindingContext as TodoItem;
var val1 = data.Prop1;
var val2 = data.Prop2;

Answer 2

您是否要在TodoItemPage的构造函数中访问BindingContext？它不应该可用。构造函数代码完成后，将调用BindingContext的setter。如果要访问它，则可以在构造函数中向此添加一个事件。并访问其值

[更新] 您无法在构造函数中访问BindingContext，因为BindingContext = e.SelectedItem as Models.TodoItem中的所有代码都已被执行后，public TodoItemPage() {...}的设置才完成。您可以根据绑定上下文执行以下操作以更新这些值

Entry m_nameentry; //to access it later outside of the constructor
public TodoItemPage()
{
    InitializeComponent();
    BindingContextChanged += TodoItemPage_BindingContextChanged; //put the code that should use the BindingContext Value inside
    //Title = "Name"; // here need show NAME - I can't display my name here
    //var nameEntry = new Entry();
    m_nameentry = new Entry();
    nameEntry.SetBinding(Entry.TextProperty, "Name");
    Content = new StackLayout
        {
            Margin = new Thickness(20),
            VerticalOptions = LayoutOptions.StartAndExpand,
            Children =
            {
                new Label { Text = "Name" },
                //nameEntry, // here NAME is shown
                m_nameentry
            }
        };
}

private void TodoItemPage_BindingContextChanged(object sender, EventArgs e)
{
    Title = (BindingContext as Models.TodoItem).Name;
    m_nameentry.Text = (BindingContext as Models.TodoItem).Name;
}

每当BindingContext更改时，这将更新您的Entry和Title。如果Models.TodoItem实现了INotifyPropertyChanged接口，并且您还希望在绑定完成后更改“名称”的值，则必须在Models.TodoItem的PropertyChangedEvent上注册并在此进行所有操作。

Answer 3

我使用两个页面，一个是Page20，另一个是Page21。 Page20中有ListView，ListView selectedItem是Page21的BindingContext。这是代码示例：

第20页：

  <ListView ItemSelected="ListView_ItemSelectedAsync" ItemsSource="{Binding items}">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <ViewCell>
                        <StackLayout Orientation="Horizontal">
                            <Label Text="{Binding Id}" />
                            <Label Text="{Binding Name}" />
                        </StackLayout>
                    </ViewCell>

                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class Page20 : ContentPage
{
    public ObservableCollection<TodoItem1> items { get; set; }
    public Page20 ()
    {
        InitializeComponent ();
        items = new ObservableCollection<TodoItem1>()
        {
            new TodoItem1(){Id=1,Name="aaa"},
            new TodoItem1(){Id=2,Name="bbb"},
            new TodoItem1(){Id=3,Name="ccc"},
            new TodoItem1(){Id=4,Name="ddd"},
            new TodoItem1(){Id=5,Name="eee"},
            new TodoItem1(){Id=6,Name="fff"},
            new TodoItem1(){Id=7,Name="ggg"},
            new TodoItem1(){Id=8,Name="hhh"}

        };
        this.BindingContext = this;
    }



    private async void ListView_ItemSelectedAsync(object sender, SelectedItemChangedEventArgs e)
    {
        await Navigation.PushAsync(new Page21 {BindingContext=e.SelectedItem as TodoItem1 });
    }
}

public class TodoItem1
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Page21

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class Page21 : ContentPage
{
    public Page21 ()
    {
        InitializeComponent ();

        Title = "Name"; // here need show NAME - I can't display my name here
        var nameEntry = new Entry();
        nameEntry.SetBinding(Entry.TextProperty, "Name");
        Content = new StackLayout
        {
            Margin = new Thickness(20),
            VerticalOptions = LayoutOptions.StartAndExpand,
            Children =
            {
                new Label { Text = "Name" },
                nameEntry, // here NAME is shown
            }
        };
    }

    private void btn1_Clicked(object sender, EventArgs e)
    {
        var data = this.BindingContext as TodoItem1;
        Console.WriteLine(data.Id);
        Console.WriteLine(data.Name);
    }
}

如何检查BindingContext中是否存在某些东西？

3 个答案: