XAML - 模板

模板描述了控制元件的整體外觀和視覺呈現。每個控制元件都與其關聯一個預設模板，該模板賦予控制元件外觀。

在 XAML 中，當您想要自定義控制元件的視覺行為和視覺外觀時，可以輕鬆建立自己的模板。邏輯和模板之間的連線可以透過資料繫結實現。

樣式和模板之間的主要區別在於：

樣式只能使用控制元件的預設屬性更改控制元件的外觀。
使用模板，您可以訪問比樣式中更多控制元件的部分。您還可以指定控制元件的現有行為和新行為。

有兩種最常用的模板型別。

控制元件模板
資料模板

控制元件模板

控制元件模板定義或指定控制元件的視覺外觀和結構。所有 UI 元素都具有一定的外觀和行為，例如，按鈕具有外觀和行為。單擊事件或滑鼠懸停事件是響應單擊和懸停而觸發的行為，並且按鈕還具有可以由控制元件模板更改的預設外觀。

讓我們再次看一個簡單的示例，其中建立了兩個具有某些屬性的按鈕。一個帶有模板，另一個帶有預設按鈕。

<Window x:Class = "TemplateDemo.MainWindow" 
   xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml" 
   Title = "MainWindow" Height = "350" Width = "604"> 
	
   <Window.Resources>
      <ControlTemplate x:Key = "ButtonTemplate" TargetType = "Button">
         <Grid>
            <Ellipse x:Name = "ButtonEllipse" Height = "100" Width = "150" >
               <Ellipse.Fill> 
                  <LinearGradientBrush StartPoint = "0,0.2" EndPoint = "0.2,1.4"> 
                     <GradientStop Offset = "0" Color = "Red"/>
                     <GradientStop Offset = "1" Color = "Orange"/>
                  </LinearGradientBrush> 
               </Ellipse.Fill>
            </Ellipse>
            <ContentPresenter Content = "{TemplateBinding Content}"
               HorizontalAlignment = "Center" VerticalAlignment = "Center" />
         </Grid>
         <ControlTemplate.Triggers> 
            <Trigger Property = "IsMouseOver" Value = "True">
               <Setter TargetName = "ButtonEllipse" Property = "Fill" >
                  <Setter.Value> 
                     <LinearGradientBrush StartPoint = "0,0.2" EndPoint="0.2,1.4"> 
                        <GradientStop Offset = "0" Color = "YellowGreen"/>
                        <GradientStop Offset = "1" Color = "Gold"/>
                     </LinearGradientBrush> 
                  </Setter.Value> 
               </Setter>
            </Trigger> 
				
            <Trigger Property = "IsPressed" Value = "True"> 
               <Setter Property = "RenderTransform"> 
                  <Setter.Value> 
                     <ScaleTransform ScaleX = "0.8" ScaleY = "0.8" CenterX = "0" CenterY = "0" /> 
                  </Setter.Value> 
               </Setter> 
					
               <Setter Property = "RenderTransformOrigin" Value = "0.5,0.5" /> 
            </Trigger>
         </ControlTemplate.Triggers>
      </ControlTemplate> 
   </Window.Resources>
	
   <StackPanel> 
      <Button Content = "Round Button!" Template = "{StaticResource ButtonTemplate}" 
         Width = "150" Margin = "50" />
      <Button Content = "Default Button!" Height = "40" Width = "150" Margin = "5" /> 
   </StackPanel> 
	
</Window>

編譯並執行上述程式碼後，將生成以下 MainWindow：

當您將滑鼠懸停在帶有自定義模板的按鈕上時，它也會更改顏色，如下所示：

資料模板

資料模板定義並指定資料集合的外觀和結構。它提供了靈活地格式化和定義任何 UI 元素上資料的呈現方式。它主要用於與資料相關的專案控制元件，例如 ComboBox、ListBox 等。

讓我們看一個數據模板的簡單示例。以下 XAML 程式碼建立了一個帶資料模板和文字塊的組合框。

<Window x:Class = "XAMLDataTemplate.MainWindow" 
   xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml" 
   Title = "MainWindow" Height = "350" Width = "604"> 
	
   <Grid VerticalAlignment = "Top">
      <ComboBox Name = "Presidents" ItemsSource = "{Binding}" Height = "30" Width = "400"> 
         <ComboBox.ItemTemplate> 
            <DataTemplate>
               <StackPanel Orientation = "Horizontal" Margin = "2">
                  <TextBlock Text = "Name: " Width = "95" Background = "Aqua" Margin = "2" /> 
                  <TextBlock Text = "{Binding Name}" Width = "95" Background = "AliceBlue" Margin = "2" /> 
                  <TextBlock Text = "Title: " Width = "95" Background = "Aqua" Margin = "10,2,0,2" />
                  <TextBlock Text = "{Binding Title}" Width = "95" Background = "AliceBlue" Margin = "2" /> 
               </StackPanel>
            </DataTemplate>
         </ComboBox.ItemTemplate> 
      </ComboBox> 
   </Grid>
   
</Window>

以下是 C# 中的實現，其中員工物件被分配給 DataContext：

using System; 
using System.Windows; 
using System.Windows.Controls;

namespace XAMLDataTemplate { 
   /// <summary> 
      /// Interaction logic for MainWindow.xaml 
   /// </summary> 
	
   public partial class MainWindow : Window {
      public MainWindow() {
         InitializeComponent(); 
         DataContext = Employee.GetEmployees(); 
      }
   }
}

以下是 C# 中 Employee 類的實現：

using System; 
using System.Collections.Generic; 
using System.Collections.ObjectModel; 
using System.ComponentModel; 
using System.Linq; 
using System.Runtime.CompilerServices; 
using System.Text; 
using System.Threading.Tasks;

namespace XAMLDataTemplate { 
   public class Employee : INotifyPropertyChanged {
      private string name; public string Name {
         get { return name; } 
         set { name = value; RaiseProperChanged(); } 
      }
      private string title; public string Title { 
         get { return title; } 
         set { title = value; RaiseProperChanged(); } 
      }
      public static Employee GetEmployee() {
         var emp = new Employee() { 
            Name = "Waqas", Title = "Software Engineer" };
         return emp; 
      }
      public event PropertyChangedEventHandler PropertyChanged;
      private void RaiseProperChanged( [CallerMemberName] string caller = ""){
         if (PropertyChanged != null) { 
            PropertyChanged(this, new PropertyChangedEventArgs(caller)); 
         } 
      }
      public static ObservableCollection<Employee> GetEmployees() {
         var employees = new ObservableCollection<Employee>();
         employees.Add(new Employee() { Name = "Ali", Title = "Developer" }); 
         employees.Add(new Employee() { Name = "Ahmed", Title = "Programmer" });
         employees.Add(new Employee() { Name = "Amjad", Title = "Desiner" });
         employees.Add(new Employee() { Name = "Waqas", Title = "Programmer" }); 
         employees.Add(new Employee() { Name = "Bilal", Title = "Engineer" });
         employees.Add(new Employee() { Name = "Waqar", Title = "Manager" }); 
         return employees; 
      }
   }
}

編譯並執行上述程式碼後，將生成以下輸出。它包含一個組合框，當您單擊組合框時，您會看到在 Employee 類中建立的資料集合被列為組合框項。

我們建議您執行上述程式碼並進行實驗。

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