XAML - 模板

模板描述控件的整体外观和视觉效果。对于每个控件，都有一个与之关联的默认模板，该模板赋予该控件外观。

在 XAML 中，当您想要自定义控件的视觉行为和视觉效果时，您可以轻松创建自己的模板。逻辑和模板之间的连接可以通过数据绑定实现。

样式和模板之间的主要区别是 −

• 样式只能使用控件的默认属性更改控件的外观。

• 使用模板，您可以访问控件的更多部分，而使用样式则不行。您还可以指定控件的现有行为和新行为。

有两种类型的模板最常用。

• 控件模板
• 数据模板

控件模板

控件模板定义或指定控件的视觉外观和结构。所有 UI 元素都具有某种外观和行为，例如，按钮具有外观和行为。单击事件或鼠标悬停事件是响应单击和悬停而触发的行为，并且按钮还有默认外观，可以通过控件模板进行更改。

让我们再看一个简单的示例，其中创建了两个具有一些属性的按钮。一个使用 template，另一个使用 default 按钮。

<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>

当编译并执行上述代码时，它将生成以下 MainWindow −

当您将鼠标悬停在具有自定义模板的按钮上时，它也会改变颜色，如下所示 −

数据模板

数据模板定义并指定数据集合的外观和结构。它提供了格式化和定义任何 UI 元素上数据呈现的灵活性。它主要用于与数据相关的项目控件，例如 ComboBox、ListBox 等。

让我们看一个简单的数据模板示例。以下 XAML 代码使用数据模板和文本块创建一个组合框。

<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# 中的实现，其中将员工对象分配给 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 Employee 类的 C# 实现 −

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; 
      }
   }
}

当上述代码被编译并执行时，它将产生以下输出。它包含一个组合框，当您单击组合框时，您会看到在 Employee 类中创建的数据集合被列为组合框项。

我们建议您执行上述代码并进行试验。