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c# - 使用具有两个视图的 mvvm？

问题描述

我有一个关于绑定的问题。我尝试在 fody.propertychanged 的​​帮助下将我的第二个视图绑定到一个空应用程序中的 Viewmodel，因为我在我的项目中做了它，但它没有工作。

所以，我做了一个干净的石板并重试，但这仍然不起作用。我不知道为什么它不起作用；这是我到目前为止所尝试的。

基础视图模型

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using PropertyChanged;

namespace TestApp
{
    [AddINotifyPropertyChangedInterface]

    public class BaseViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public void SetProperty<T>(ref T storage, T value, string propertyName)
        {
            storage = value;
            RaisePropertyChangedEvent(propertyName);
        }

        protected void RaisePropertyChangedEvent(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

浏览视图模型

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Input;
using System.Threading;
using System.Threading.Tasks;
using System.Configuration;
using System.Collections.Specialized;
using System.IO;

namespace TestApp
{
    public class BrowseViewModel : BaseViewModel
    {


        #region public variables
        private string _webUrl;
        public string WebUrl
        {
            get => _webUrl;
            set
            {
                //This will change based on how you have implemented your BaseViewModel!
                //The method name might be different, or have different parameters!
                this.SetProperty(ref _webUrl, value, nameof(WebUrl));
                //Call the save file path validation method...
                SaveFilePath();
            }
        }

        private string _errorMessage;
        public string ErrorMessage
        {
            get => _errorMessage;
            private set
            {
                //This will change based on how you have implemented your BaseViewModel!
                //This method should call NotifyPropertyChange to notify the UI to update...
                this.SetProperty(ref _errorMessage, value, nameof(ErrorMessage));
            }
        }
        #endregion


        #region Public Commands
        public ICommand SaveCommand { get; set; }
        #endregion

        #region Constructor
        public BrowseViewModel()
        {
            this.SaveCommand = new RelayCommand(SaveFilePath);
        }
        #endregion

        #region Private methods
        private void SaveFilePath()
        {
            if (File.Exists(_webUrl))
            {
                _errorMessage = "String works";
            }
            else
            {
                _errorMessage = "Filen existerar ej";
            }



        }



        #endregion







    }
}

主窗口.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace TestApp
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            BrowseWindow browse = new BrowseWindow();


            browse.Show();
            browse.DataContext = new BrowseViewModel();
            InitializeComponent();
        }
    }
}

浏览窗口.xaml

<Window x:Class="TestApp.BrowseWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:TestApp"
        mc:Ignorable="d"
        Title="BrowseWindow" Height="450" Width="800">
    <Grid>
        <Label Content="{Binding errorMessage}" HorizontalAlignment="Left" Margin="10,383,0,0" VerticalAlignment="Top" />
        <Button Content="Button" HorizontalAlignment="Left" Margin="684,368,0,0" VerticalAlignment="Top" Width="75" Command="{Binding SaveCommand}"/>

    </Grid>
</Window>

浏览窗口

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace TestApp
{
    /// <summary>
    /// Interaction logic for BrowseWindow.xaml
    /// </summary>
    public partial class BrowseWindow : Window
    {
        public BrowseWindow()
        {
            InitializeComponent();
            this.DataContext = new BrowseViewModel(); 
        }
    }
}

中继命令

using System;
using System.Windows.Input;

namespace TestApp
{
    public class RelayCommand : ICommand
    {
        #region Public events
        /// <summary>
        /// Eventet som används när <see cref="CanExecute(object)"/> värdet har ändrats
        /// </summary>
        public event EventHandler CanExecuteChanged = (sender, e) => { };
        #endregion

        #region Private members
        private Action mAction;
        #endregion

        #region Constructor

        /// <summary>
        /// Standard Konstruktor
        /// </summary>
        public RelayCommand(Action action)
        {
            mAction = action;
        }
        #endregion

        #region Command Methods
        /// <summary>
        /// Ett action Kommando kan alltid köras
        /// </summary>
        /// <param name="parameter"></param>
        /// <returns></returns>
        public bool CanExecute(object parameter)
        {
            return true;
        }

        public void Execute(object parameter)
        {
            mAction();
        }
        #endregion
    };
}

标签： c#mvvmdata-binding

解决方案

当您更改私有字段的值时，_errorMessage您可以解决该属性设置器ErrorMessage将通知该属性更改。

您必须将新值分配给属性本身才能让设置器代码进入游戏。

private void SaveFilePath()
{
    if (File.Exists(_webUrl))
    {
        ErrorMessage = "String works";
    }
    else
    {
        ErrorMessage = "Filen existerar ej";
    }
}

更新

我刚刚在您的 XAML 中看到另一个绑定错误

<Label Content="{Binding errorMessage}" .../>

但它区分大小写，因此您必须使用正确的名称，而不是某些名称

<Label Content="{Binding ErrorMessage}" .../>

在调试时，您应该始终检查输出窗口是否存在绑定错误。

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