- MVVM 教程
- MVVM - 首页
- MVVM – 简介
- MVVM - 优势
- MVVM - 职责
- MVVM - 第一个应用程序
- MVVM – 视图绑定
- MVVM – 绑定ViewModel
- MVVM – WPF 数据绑定
- MVVM – WPF 数据模板
- MVVM – ViewModel 通信
- MVVM – 层次结构与导航
- MVVM – 验证
- MVVM – 依赖注入
- MVVM – 事件
- MVVM – 单元测试
- MVVM – 框架
- MVVM – 面试问题
- MVVM 有用资源
- MVVM - 快速指南
- MVVM - 有用资源
- MVVM - 讨论
MVVM – 视图绑定
本章将介绍将视图与 ViewModel 绑定起来的不同方法。首先，让我们看一下视图优先构建，我们可以在 XAML 中声明它。正如我们在上一章中看到的例子，我们已经从主窗口绑定了一个视图。现在我们将看到其他绑定视图的方法。
本章也将使用相同的示例。以下是相同的模型类实现。
using System.ComponentModel;
namespace MVVMDemo.Model {
public class StudentModel {}
public class Student : INotifyPropertyChanged {
private string firstName;
private string lastName;
public string FirstName {
get { return firstName; }
set {
if (firstName != value) {
firstName = value;
RaisePropertyChanged("FirstName");
RaisePropertyChanged("FullName");
}
}
}
public string LastName {
get { return lastName; }
set {
if (lastName != value) {
lastName = value;
RaisePropertyChanged("LastName");
RaisePropertyChanged("FullName");
}
}
}
public string FullName {
get {
return firstName + " " + lastName;
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string property) {
if (PropertyChanged != null) {
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
}
}
这是 ViewModel 类实现。这次 LoadStudents 方法在默认构造函数中被调用。
using MVVMDemo.Model;
using System.Collections.ObjectModel;
namespace MVVMDemo.ViewModel{
public class StudentViewModel {
public StudentViewModel() {
LoadStudents();
}
public ObservableCollection<Student> Students {
get;
set;
}
public void LoadStudents() {
ObservableCollection<Student> students = new ObservableCollection<Student>();
students.Add(new Student { FirstName = "Mark", LastName = "Allain" });
students.Add(new Student { FirstName = "Allen", LastName = "Brown" });
students.Add(new Student { FirstName = "Linda", LastName = "Hamerski" });
Students = students;
}
}
}
无论视图是窗口、用户控件还是页面，解析器通常自上而下、从左到右工作。它在遇到每个元素时调用其默认构造函数。构建视图有两种方法。您可以使用任何一种。
- 在 XAML 中进行视图优先构建
- 在代码隐藏中进行视图优先构建
在 XAML 中进行视图优先构建
一种方法是简单地将您的 ViewModel 作为 DataContext 属性设置程序中的嵌套元素添加，如下面的代码所示。
<UserControl.DataContext> <viewModel:StudentViewModel/> </UserControl.DataContext>
这是完整的视图 XAML 文件。
<UserControl x:Class="MVVMDemo.Views.StudentView"
xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d = "http://schemas.microsoft.com/expression/blend/2008"
xmlns:local = "clr-namespace:MVVMDemo.Views"
xmlns:viewModel = "clr-namespace:MVVMDemo.ViewModel"
mc:Ignorable = "d"
d:DesignHeight = "300" d:DesignWidth = "300">
<UserControl.DataContext>
<viewModel:StudentViewModel/>
</UserControl.DataContext>
<Grid>
<StackPanel HorizontalAlignment = "Left">
<ItemsControl ItemsSource = "{Binding Path = Students}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation = "Horizontal">
<TextBox Text = "{Binding Path = FirstName, Mode = TwoWay}"
Width = "100" Margin = "3 5 3 5"/>
<TextBox Text = "{Binding Path = LastName, Mode = TwoWay}"
Width = "100" Margin = "0 5 3 5"/>
<TextBlock Text = "{Binding Path = FullName, Mode = OneWay}"
Margin = "0 5 3 5"/>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</Grid>
</UserControl>
在代码隐藏中进行视图优先构建
另一种方法是，您可以通过在视图的代码隐藏中设置 DataContext 属性来实现视图优先构建。
通常，DataContext 属性在视图的构造函数方法中设置，但您也可以将其构造推迟到视图的 Load 事件触发。
using System.Windows.Controls;
namespace MVVMDemo.Views {
/// <summary>
/// Interaction logic for StudentView.xaml
/// </summary>
public partial class StudentView : UserControl {
public StudentView() {
InitializeComponent();
this.DataContext = new MVVMDemo.ViewModel.StudentViewModel();
}
}
}
在代码隐藏中而不是在 XAML 中构建视图模型的一个原因是，视图模型构造函数需要参数，但 XAML 解析只能在默认构造函数中定义时构建元素。
现在在这种情况下，视图的 XAML 文件将如下面的代码所示。
<UserControl x:Class = "MVVMDemo.Views.StudentView"
xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d = "http://schemas.microsoft.com/expression/blend/2008"
xmlns:local = "clr-namespace:MVVMDemo.Views"
mc:Ignorable = "d"
d:DesignHeight = "300"
d:DesignWidth = "300">
<Grid>
<StackPanel HorizontalAlignment = "Left">
<ItemsControl ItemsSource = "{Binding Path = Students}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel Orientation = "Horizontal"<
<TextBox Text = "{Binding Path = FirstName, Mode = TwoWay}"
Width = "100" Margin = "3 5 3 5"/>
<TextBox Text = "{Binding Path = LastName, Mode = TwoWay}"
Width = "100" Margin = "0 5 3 5"/>
<TextBlock Text = "{Binding Path = FullName, Mode = OneWay}"
Margin = "0 5 3 5"/>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</Grid>
</UserControl>
您可以在 MainWindow 中声明此视图，如 MainWindow.XAML 文件所示。
<Window x:Class = "MVVMDemo.MainWindow"
xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d = "http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local = "clr-namespace:MVVMDemo"
xmlns:views = "clr-namespace:MVVMDemo.Views"
mc:Ignorable = "d"
Title = "MainWindow" Height = "350" Width = "525">
<Grid>
<views:StudentView x:Name = "StudentViewControl"/>
</Grid>
</Window>
编译并执行上述代码后，您将在主窗口上看到以下输出。
我们建议您逐步执行以上示例，以便更好地理解。
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