Silencejql
0%

WPF MVVM示例一

发表于 分类于 ， Valine：
本文字数： 3.3k 阅读时长 ≈ 3 分钟

深入浅出WPF示例, 理解Binding实现

示例

功能: 实现按钮计算更新TextBox数据

Cal

数据属性NotificationObject

当属性被赋值时调用RaisePropertyChanged触发PropertyChanged

1
2
3
4
5
6
7
8
9
public class NotificationObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public void RaisePropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

命令属性DelegateCommand

View中按钮按下等触发命令后执行Execute

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
public class DelegateCommand : ICommand
{
    public event EventHandler CanExecuteChanged;

    public bool CanExecute(object parameter)
    {
        if(CanExcuteFunc == null)
            return true;
        return CanExcuteFunc(parameter);
    }

    public void Execute(object parameter)
    {
        if (ExecuteAction == null)
            return;
        ExecuteAction(parameter);
    }

    public Action<object> ExecuteAction { get; set; }

    public Func<object, bool> CanExcuteFunc { get; set; }
}

MainWindowViewModel

示例中Cal``Button按下后触发执行CanExecute若返回true则执行Execute, 在构造中添加ExecuteAction执行方法

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
public class MainWindowViewModel : NotificationObject
{
	private double num1;

	public double Num1
	{
		get { return num1; }
		set
		{
			num1 = value;
			RaisePropertyChanged(nameof(Num1));
		}
    }

    private double num2;

    public double Num2
    {
        get { return num2++; }
        set
        {
            num2 = value;
            RaisePropertyChanged(nameof(Num2));
        }
    }

    private double num3;

    public double Num3
    {
        get { return num3; }
        set
        {
            num3 = value;
            RaisePropertyChanged(nameof(Num3));
        }
    }

    public DelegateCommand AddCommand { get; set; }

    void Add(object param)
    {
        Num3 = Num1 + Num2;
    }
    public MainWindowViewModel()
    {
        AddCommand = new DelegateCommand
        {
            ExecuteAction = Add
        };
    }
}

数据层DataContext

DataContext = new MainWindowViewModel();

指定Banding上下文即业务逻辑

如上述示例 Banding绑定的是MainWindowViewModel类里的属性名

DataContext设置方法

1. 初始化时添加
1
2
3
4
5
public MainWindow()
{
    InitializeComponent();
    this.DataContext = new MainWindowViewModel();
}
2. xaml中d:DataContext指定
1
2
xmlns:viewmodel="clr-namespace:LearnWpf.ViewModel" 
d:DataContext="{d:DesignInstance Type=viewmodel:MainWindowViewModel}"
3. xaml中添加
1
2
3
<Window.DataContext>
    <viewmodel:MainWindowViewModel/>
</Window.DataContext>

Banding DataContext说明

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
<!-- 注意此时我已经在初始化代码中设置DataContext 为 ClassA，DataContext = new ClassA -->
<Window x:Name="MyWindow">
	<!-- DataContext 没有被指定,所以继承自父类 的 DataContext,也就是 ClassA -->
	<StackPanel>
		<!-- DataContext 继承自父类,也就是 ClassA, 所以这里会显示 ClassA.Name -->
		<Label Content="{Binding Name}"/>
		<!-- DataContext 仍然是ClassA, 但是我们通过binding设置为ClassA.ClassB-->
		<StackPanel DataContext="{Binding ClassB}">
			<!-- DataContext 继承自父类，也就是ClassB，所以这里会显示 ClassB.Name -->
			<Label Content="{Binding Name}"/>
			<!-- DataContext i仍然是 ClassB, 但是我们binding 到了Window's DataContext.Name, 也就是 ClassA.Name -->
			<Label Content="{Binding ElementName=MyWindow, Path=DataContext.Name}"/>
		</StackPanel>
		<!-- We've left the StackPanel with its DataContext bound to ClassB, so this Label's DataContext is ClassA (inherited from parent StackPanel), and we are binding to ClassA.ClassB.Name -->
		<Label Content="{Binding ClassB.Name}"/>
	</StackPanel>
</Window>