01

—

介紹

IValueConverter介面位於名稱空間System.Windows.Data，介面定義了Convert和ConvertBack兩組方法：

 public interface IValueConverter
    {
        object Convert(object value, Type targetType, object parameter, CultureInfo culture);
        object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture);
    }
}

在介面控制元件所需資料型別或格式和後臺繫結的資料不一致時，往往需要藉助IValueConverter介面進行轉換。

02

—

舉例

• 介面新增一個表格控制元件datagrid，繫結資料結構StudentList，StudentList這是一個ObservableCollection<Students>集合；

• Students資料模型定義如下：其中重寫了ToString方法，並定義了四個屬性，分別是Id，Name ，Age 和AgeValidate ，AgeValidate 用來驗證資料，即年齡小於16或者大於21,時介面字型顯示紅色

•  [AddINotifyPropertyChangedInterface]
      public class Students 
      {
          private int id;
          public int Id
          {
              get { return id; }
              set
              {
                  id = value;
              }
          }
          public string Name { get; set; }
  
          private int age;
          public int Age 
          {
              get { return age; }
              set
              {
                  age = value;
                  if(age < 16 || age > 21 )
                  {
                      AgeValidate = true;
                  }
                  else
                  {
                      AgeValidate = false;
                  }
              }
          }
  
          public bool AgeValidate { get; set; }
          public override string ToString()
          {
              StringBuilder report = new StringBuilder();
              report.AppendLine($"[Id]  = [{Id}]");
              report.AppendLine($"[Name]  = [{Name}]");
              report.AppendLine($"[Age]  = [{Age}]");
              report.AppendLine($"[AgeValidate]  = [{AgeValidate}]");
              return report.ToString();
          }
      }
  

  　　介面前臺繫結：主要是通過這句

•  Foreground="{Binding AgeValidate,Converter={StaticResource ShowColorConverter}}"
  

  　　datagrid全部的程式碼如下：

•  <DataGrid Name="dgSourceData" AutoGenerateColumns="False" ItemsSource="{Binding StudentList}" 
                    ContextMenu="{Binding menu1}" RowHeaderWidth="30"  SelectedItem ="{Binding SelectedItems}" SelectionMode="Single" SelectionUnit="Cell"
                                  cal:Message.Attach="[Event SelectionChanged]=[GridControl_SelectionChanged($source,$eventArgs)];" 
                                 CellEditEnding="dgSourceData_BeginningEdit" SelectionChanged="dgSourceData_SelectionChanged" >
              <DataGrid.Columns>
                  <DataGridTextColumn Header="Name"  Binding="{ Binding Path=Name}" MinWidth="68"/>
                  <DataGridTemplateColumn  Header="Age"  MinWidth="68" >
                      <DataGridTemplateColumn.CellTemplate>
                          <DataTemplate>
                              <TextBox Text="{Binding Path=Age,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
                                       Foreground="{Binding AgeValidate,Converter={StaticResource ShowColorConverter}}" />
                          </DataTemplate>
                      </DataGridTemplateColumn.CellTemplate>
                  </DataGridTemplateColumn>
                  <DataGridTextColumn Header="Id"  Binding="{ Binding Path=Id}" MinWidth="48"/>
              </DataGrid.Columns>
          </DataGrid>
  

  　　定義資源

•  <UserControl.Resources>
          <converters:ShowColorConverter x:Key="ShowColorConverter" />
      </UserControl.Resources>
  

  　　

  IValueConverter介面實現：注意需要將object型別的value轉換為我們的目標型別bool量

  public class ShowColorConverter : IValueConverter
      {
          public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
          {
              var flag = (bool)value;
              if (flag)
              {
                  return "Red";
              }
              else
              {
                  return "Black";
              }
          }
  
          public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
          {
              throw new NotImplementedException();
          }
      }
  

  　

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