在本文中，将探讨如何使用MVVM模式创建一个应用程序，该程序不仅能够过滤数据，还能将数据导出到Excel。这种模式支持数据的解耦和代码的可重用性，使得程序更加清晰和易于维护。
在工作过程中，被分配了一个任务，需要创建一个展示数据的应用程序。这些数据需要按照类似于Windows文件过滤的方式进行过滤。作为一个MVVM模式的坚定支持者，希望代码能够保持清晰、解耦，并且具有通用性，以便在其他情况下也能使用。
由于ListView需要处理所有类型的数据，希望过滤和导出的决定权由ViewModel来掌握。这样，就可以根据学生的私人名字来过滤学生详细信息的列表，或者只根据制造商来过滤汽车的列表。为了处理这个任务，创建了一个接口，ViewModel必须实现这个接口：
public interface IEnhancedListObject
{
bool Filter(string strFilter);
void WriteHeaderIntoExcelSheet(Worksheet worksheet, ref int nRow, ref int nColumn);
void WriteDataIntoExcelSheet(Worksheet worksheet, ref int nRow, ref int nColumn);
}
这个接口包含三个方法：Filter用于决定元素是否通过给定的字符串过滤；WriteHeaderIntoExcelSheet用于将导出数据的列写入Excel工作表；WriteDataIntoExcelSheet用于将实际数据写入Excel工作表。
为了使代码尽可能健壮，尽量避免在Xaml.cs文件中编写任何代码。使用了附加属性来处理这个问题。
public class ListViewFilterExtension
{
public static readonly DependencyProperty FilterSourceProperty =
DependencyProperty.RegisterAttached("FilterSource", typeof(TextBox), typeof(ListViewFilterExtension), new FrameworkPropertyMetadata(null, new PropertyChangedCallback(OnTextBoxSet)));
public static TextBox GetFilterSource(DependencyObject d)
{
return (TextBox)d.GetValue(FilterSourceProperty);
}
public static void SetFilterSource(DependencyObject d, TextBox value)
{
d.SetValue(FilterSourceProperty, value);
}
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;
return filterableObject.Filter(textFilter.Trim());
};
};
}
}
}
过滤假设过滤字符串将从TextBox中获取。附加属性被赋予一个TextBox作为参数，并将自己注册为TextChanged事件的监听器。它注册的委托遍历ListView.ItemSource中的元素，假设它们实现了IEnhancedListObject接口，并在它们上运行过滤操作。
导出附加属性假设它将被一个Button使用。它获取一个ListView作为其参数。它将自己注册到Button.Click操作。点击时，它遍历ListView.ItemsSource，假设它们实现了IEnhancedListObject接口，并使用接口将数据添加到Excel工作表中。
public class ListViewExcelExporterExtension
{
public static readonly DependencyProperty ExcelExporterProperty =
DependencyProperty.RegisterAttached("ExcelExporter", typeof(ListView), typeof(ListViewExcelExporterExtension), new FrameworkPropertyMetadata(null, new PropertyChangedCallback(OnExcelExportRequest)));
public static ListView GetExcelExporter(DependencyObject d)
{
return (ListView)d.GetValue(ExcelExporterProperty);
}
public static void SetExcelExporter(DependencyObject d, ListView value)
{
d.SetValue(ExcelExporterProperty, value);
}
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;
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)
{
worksheet._DisplayRightToLeft = 0;
if (listView.Items.Count > 0)
{
IEnhancedListObject vm = listView.Items[0] as IEnhancedListObject;
int nRow = 1;
int nColumn = 1;
if (vm != null)
{
vm.WriteHeaderIntoExcelSheet(worksheet, ref nRow, ref nColumn);
}
foreach (var item in listView.Items)
{
vm = item as IEnhancedListObject;
vm.WriteDataIntoExcelSheet(worksheet, ref nRow, ref nColumn);
}
}
}
Thread.CurrentThread.CurrentCulture = currentCulture;
};
}
}
}