C# WPF 绑定不从属性中获取数据

Question

In my XAML I am doing the following

<Label Content="{Binding ElementName=Root, Path=UserData.Email, Mode=OneWay}" />

the Root element is my Window itself and the UserData Is a get; private set; get; private set; auto property in my codebehind file, the Email property is get-only and is of type string .

the UserData object gets set after the user has logged in. But the binding is not taking the value from the object. I have verified that the object does indeed contain the correct data and isn't null . What am I missing here?

Answer 1

I went ahead and created a hello world version for this. Here is the xml. This should simply change the banner when the button is clicked to the text in the text box. I couldn't find a super simple example so I just made one. Obviously there are way more advanced ways to do this but it should make for a simple version to build from.

<Window x:Class="Hello_World.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Label Name="MyLabel" Content="{Binding MyLabel}" HorizontalAlignment="Left" Margin="58,37,0,0" VerticalAlignment="Top" Height="65" Width="423" FontSize="44"/>
        <TextBox Name="MyTextBox" HorizontalAlignment="Left" Height="28" Margin="163,162,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="163"/>
        <Button Content="Change Banner" HorizontalAlignment="Left" Margin="251,209,0,0" VerticalAlignment="Top" Width="109" Click="Button_Click"/>

    </Grid>
</Window>

Next is the ModelView that implements the INotifyPropertyChanged interface. Note that your properties must be public properties with a getter, setter and backing field. This allows you to call the OnPropetyChanged() method whenever the property is set.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Hello_World
{
    public class MainViewModel: INotifyPropertyChanged
    {


        private string _myLabel;

        public string MyLabel
        {
            get { return _myLabel; }
            set
            {
                _myLabel = value;
                OnPropertyChanged(nameof(MyLabel));
            }
        }    

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propetyName)
        {
            if(PropertyChanged != null)
            PropertyChanged(this,new PropertyChangedEventArgs(propetyName));

        }

    }
}

Lastly the MainWindow. Set the DataContext in the main constructor. Note I could have set the DataContext of the main grid and all of its children would inherit the same DataContext . This would keep you from having to set all of the components' individually.

namespace Hello_World
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private MainViewModel MyViewModel;


        public MainWindow()
        {
            InitializeComponent();
            MyViewModel = new MainViewModel();

            // Here's where I'm setting the object to look at.
            DataContext = MyViewModel;

            // Now I don't need to access the textbox directly.
            MyViewModel.MyLabel = "Hello World";    
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            // Note: ICommand is a more advanced topic.
            MyViewModel.MyLabel = MyTextBox.Text;
        }
    }
}