使用 MVVM 增强 ListView 操作

• 下载源代码 - 44.8 KB

引言

本文介绍如何创建一个具有扩展功能的 ListView，例如对其数据进行过滤和导出到 Excel，同时支持 MVVM 模式，并且 ListView.ItemsSource 的类型不会成为障碍，同时还能够确定每种类型如何进行过滤。

背景

我被分配了一项工作任务，即创建一个呈现一些数据的应用程序。这些数据需要以类似于 Windows 文件过滤的方式进行过滤。作为 MVVM 的坚定支持者，我希望我的代码干净、解耦，并且通用，以便也可以在其他情况下使用。

使用代码

由于 ListView 需要处理所有数据类型，我希望 ViewModel 决定如何进行过滤和导出。因此，我可以有一个学生详细信息的列表，通过学生的私人姓名进行过滤，以及一个汽车列表，仅通过制造商进行过滤。为了处理此任务，我创建了一个接口，ViewModel 必须实现该接口

/// <summary>
/// This is an iterface for every object which
/// can have its data filtered given a certain string
/// </summary>
public interface IEnhancedListObject
{
    /// <summary>
    /// Filter the data given a filter string
    /// </summary>
    /// <param name="strFilter"></param>
    /// <returns></returns>
    bool Filter(string strFilter);
    /// <summary>
    /// Write the Header into the excel sheet
    /// </summary>
    /// <param name="worksheet">The worksheet to use</param>
    /// <param name="nRow">The row to start with</param>
    /// <param name="nColumn">The column to start with</param>
    /// <returns></returns>
    void WriteHeaderIntoExcelSheet(Worksheet worksheet, ref int nRow, ref int nColumn);
    /// <summary>
    /// Write the data into an Excel worksheet
    /// </summary>
    /// <param name="worksheet">The worksheet to use</param>
    /// <param name="nRow">The row to start with</param>
    /// <param name="nColumn">The column to start with</param>
    /// <returns></returns>
    void WriteDataIntoExcelSheet(Worksheet worksheet, ref int nRow, ref int nColumn);
}

该接口包含三个方法

• Filter：决定元素是否通过给定的字符串。
• WriteHeaderIntoExcelSheet：写入导出的数据的列。
• WriteDataIntoExcelSheet：将实际数据写入 Excel 表格。

为了使我的代码尽可能健壮，我尝试避免在 Xaml.cs 文件中编写任何代码。为此，我使用了附加属性。

过滤

public class ListViewFilterExtension
{
    /// <summary>
    /// FilterSource Attached Dependency Property
    /// </summary>
    public static readonly DependencyProperty FilterSourceProperty =
        DependencyProperty.RegisterAttached("FilterSource",
        typeof(TextBox), typeof(ListViewFilterExtension),
            new FrameworkPropertyMetadata(null,
                new PropertyChangedCallback(OnTextBoxSet)));


    /// <summary>
    /// Gets the FilterSource property.
    /// </summary>
    public static TextBox GetFilterSource(DependencyObject d)
    {
        return (TextBox)d.GetValue(FilterSourceProperty);
    }

    /// <summary>
    /// Sets the FilterSource property.
    /// </summary>
    public static void SetFilterSource(DependencyObject d, TextBox value)
    {
        d.SetValue(FilterSourceProperty, value);
    }

    /// <summary>
    /// Handles changes to the FilterSource property.
    /// </summary>
    private static void OnTextBoxSet(DependencyObject d,
        DependencyPropertyChangedEventArgs e)
    {
        ListView listView = d as ListView;
        TextBox textBox = e.NewValue as TextBox;

        if ((listView != null) && (textBox != null))
        {
            textBox.TextChanged += delegate(object sender, 
                                     TextChangedEventArgs tcea)
            {
                ICollectionView view =
                    CollectionViewSource.GetDefaultView(listView.ItemsSource);
                view.Filter = null;
                view.Filter = delegate(object obj)
                {
                    IEnhancedListObject filterableObject = obj as IEnhancedListObject;
                    if (filterableObject == null) return false;

                    string textFilter = ((TextBox)sender).Text;

                    if (textFilter.Trim().Length == 0) return true;
                    // the filter is empty - pass all items

                    return filterableObject.Filter(textFilter.Trim());
                };
            };
        }
    }
}

过滤假定过滤器字符串将从 TextBox 中获取。附加属性将 TextBox 作为参数，并将其注册为 TextChanged 事件的侦听器。它注册的委托遍历 ListView.ItemSource 中的元素，假设它们正在实现 IEnhancedListObject 接口，并在它们上运行过滤操作。

导出到 Excel

public class ListViewExcelExporterExtension
{
    /// <summary>
    /// ExcelExporter Attached Dependency Property
    /// </summary>
    public static readonly DependencyProperty ExcelExporterProperty =
        DependencyProperty.RegisterAttached("ExcelExporter",
        typeof(ListView), typeof(ListViewExcelExporterExtension),
            new FrameworkPropertyMetadata(null,
                new PropertyChangedCallback(OnExcelExportRequest)));


    /// <summary>
    /// Gets the ExcelExporter property. 
    /// </summary>
    public static ListView GetExcelExporter(DependencyObject d)
    {
        return (ListView)d.GetValue(ExcelExporterProperty);
    }

    /// <summary>
    /// Sets the ExcelExporter property. 
    /// </summary>
    public static void SetExcelExporter(DependencyObject d, ListView value)
    {
        d.SetValue(ExcelExporterProperty, value);
    }

    /// <summary>
    /// Handles changes to the FilterSource property.
    /// </summary>
    private static void OnExcelExportRequest(DependencyObject d,
        DependencyPropertyChangedEventArgs e)
    {
        System.Windows.Controls.Button button = d as System.Windows.Controls.Button;
        ListView listView = e.NewValue as ListView;

        if ((button != null) && (listView != null))
        {
            button.Click += delegate(object sender, RoutedEventArgs er)
            {
                Microsoft.Office.Interop.Excel.Application application =
                    new Microsoft.Office.Interop.Excel.Application();
                application.Visible = true;

                // Workaround to fix MCST bug - The threads culture
                //          info must be en-US for the Excel sheet
                //          to open properly
                CultureInfo currentCulture = Thread.CurrentThread.CurrentCulture;
                Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US"); 

                Workbook workbook = application.Workbooks.Add(Missing.Value);
                Worksheet worksheet = workbook.ActiveSheet as Worksheet;
                if (worksheet != null)
                {
                    // Set the display to show from left to right
                    worksheet._DisplayRightToLeft = 0;

                    if (listView.Items.Count > 0)
                    {
                        // Write the header
                        IEnhancedListObject vm = listView.Items[0] as IEnhancedListObject;
                        int nRow = 1;
                        int nColumn = 1;
                        if (vm != null)
                        {
                            vm.WriteHeaderIntoExcelSheet(worksheet, ref nRow, ref nColumn);
                        }
                        // Write all the elements in the view model
                        foreach (var item in listView.Items)
                        {
                            vm = item as IEnhancedListObject;
                            vm.WriteDataIntoExcelSheet(worksheet, ref nRow, ref nColumn);
                        }
                    }
                }
                // Work around MSFT bug - return the culture info to the previous set
                Thread.CurrentThread.CurrentCulture = currentCulture; 
            };
        }
    }
}

导出附加属性假定它将由 Button 使用。它将 ListView 作为其参数。它注册到 Button.Click 操作。单击后，它遍历 ListView.ItemsSource，假设它们正在实现 IEnhancedListObject 接口，并使用该接口将数据添加到 Excel 表格中。

在示例中，我展示了 S&P 指数中 500 家公司的列表，我从 Wikipedia 获取的。

历史

• 2010年6月29日：初始版本。