Question

我正在学习MVVM。由于我看过很多教程或项目只使用View和ViewModel，我有点困惑。这是我的代码。

模特：

public class StudentModel : PropertyChangedBase
{
    private String _firstName;
    public String FirstName
    {
        get { return _firstName; }
        set
        {
            _firstName = value;
            NotifyOfPropertyChange(() => FirstName);
        }
    }

    private Double _gradePoint;
    public Double GradePoint
    {
        get { return _gradePoint; }
        set
        {
            _gradePoint = value;
            NotifyOfPropertyChange(() => GradePoint);
        }
    }
}

查看：

<UserControl x:Class="MVVMLearningWithCaliburnMicro.Views.StudentView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:cal="http://www.caliburnproject.org">
    <Grid Width="525" Height="300" Background="Lavender">
        <DockPanel>
            <TextBlock HorizontalAlignment="Center" Text="Student Data"
                       DockPanel.Dock="Top" FontSize="20" />
            <StackPanel Orientation="Vertical" HorizontalAlignment="Center"
                        VerticalAlignment="Stretch"
                        Margin="0,8" DockPanel.Dock="Top">
                <StackPanel Orientation="Horizontal" Margin="0,5">
                    <TextBlock Text="Name" FontSize="15" Margin="5,0" />
                    <TextBox Name="txtName" Text="{Binding Path=Student.FirstName}" Width="250" />
                </StackPanel>
                <StackPanel Orientation="Horizontal" Margin="0,5">
                    <TextBlock Text="Grade" FontSize="15" Margin="5,0" />
                    <TextBox Name="txtGrade" Text="{Binding Path=Student.GradePoint}" Width="250" />
                </StackPanel>
            </StackPanel>
            <StackPanel Orientation="Horizontal" Margin="0,5" HorizontalAlignment="Center"
                        VerticalAlignment="Bottom"
                        DockPanel.Dock="Bottom">
                <Button Name="btnSave" Width="100" Height="40"
                        cal:Message.Attach="SaveStudent">
                    <TextBlock Text="Save" FontSize="15" />
                </Button>
            </StackPanel>
        </DockPanel>
    </Grid>
</UserControl>

VIEWMODEL：

public class StudentViewModel
{
    public StudentModel Student { get; set; }

    public void SaveStudent()
    {
        MessageBox.Show(String.Format("Saved: {0} - ({1})", Student.FirstName, Student.GradePoint));
    }

    public StudentViewModel()
    {
        Student = new StudentModel { FirstName = "Tom Johnson", GradePoint = 3.7 };
    }

    private Boolean CanSaveStudent()
    {
        return Student.GradePoint >= 0.0 || Student.GradePoint <= 4.0;;
    }
}

问：
1.我如何设置我的警卫财产，因为NotifyOfPropertyChange()是在模型中？ 2.（愚蠢的问题）我的MVVM模式是否指向正确的方式？

Answer 1

一种解决方案是从PropertyChangedBase继承viewmodel并订阅StudentModel的属性更改。然后将guard方法转换为属性，如下所示：

public class StudentViewModel: PropertyChangedBase
{
    public StudentModel Student { get; set; }

    public void SaveStudent()
    {
        MessageBox.Show(String.Format("Saved: {0} - ({1})", Student.FirstName, Student.GradePoint));
    }

    public StudentViewModel()
    {
        Student = new StudentModel { FirstName = "Tom Johnson", GradePoint = 3.7 };
        Student.PropertyChanged += delegate { NotifyOfPropertyChanged( () => CanSaveStudent)};
    }

    public Boolean CanSaveStudent
    {
        get 
        {
            return Student.GradePoint >= 0.0 || Student.GradePoint <= 4.0;
        }
    }
}

希望它有效。

Answer 2

通知事件应出现在view model中，因为它会传递来自model的更改并将其推送到用户界面，反之亦然。这是根据MVVM设计指南。

在您的具体情况下，您可以保留或保留原样，但删除不必要的view model，或移动view model

中的通知

Answer 3

您的通知更改应该在模型中，因为这也是您的约束。基本上，您的视图模型应该加载对象列表，并为大多数事物提供绑定集合到UI。您上面的实现似乎是一个具有单个对象的详细面板（例如编辑模式）。

总结一下。

ViewModel - 应该实现INotifyPropertyChangeed接口模型 - 应该实现INotifyPropertyChangeed接口

要启用/禁用命令/按钮，您应该使用命令绑定。我有一个你可以参考的WPF和Silverlight教程。

http://tsells.wordpress.com/2010/06/23/command-binding-with-wpf-and-silverlight-net-4-0-with-m-v-vm/

在过去的几年里，我还提出了一些关于这件事的教程。如果你愿意，请检查出来......

http://tsells.wordpress.com/2011/02/08/using-reflection-with-wpf-and-the-inotifypropertychanged-interface/

http://tsells.wordpress.com/2010/06/02/wpf-model-view-viewmodel-m-v-vm-example/

Answer 4

好的，我的代码中有一个结论这是我的灵感

@tsells - 感谢第3个链接

@john polvora - 感谢指出该物业
重要提示：应该是公共财产

Guard Clause Not Firing
Error on guard clause with Caliburn.Micro

这里的代码我认为更清洁

模特：

public class StudentModel
{
    public String FirstName { get; set; }
    public Double GradePoint { get; set; }
}

查看：

<UserControl x:Class="MVVMWithCMTwo.Views.StudentView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
             xmlns:cal="http://www.caliburnproject.org">
    <Grid Width="525" Height="300" Background="Lavender">
        <DockPanel>
            <TextBlock HorizontalAlignment="Center" Text="Student Data"
                       DockPanel.Dock="Top" FontSize="20" />
            <StackPanel Orientation="Vertical" HorizontalAlignment="Center"
                        VerticalAlignment="Stretch"
                        Margin="0,8" DockPanel.Dock="Top">
                <StackPanel Orientation="Horizontal" Margin="0,5">
                    <TextBlock Text="Name" FontSize="15" Margin="5,0" />
                    <TextBox Name="txtName" Text="{Binding Path=StudentName}" Width="250" />
                </StackPanel>
                <StackPanel Orientation="Horizontal" Margin="0,5">
                    <TextBlock Text="Grade" FontSize="15" Margin="5,0" />
                    <TextBox Name="txtGrade" Text="{Binding Path=StudentGrade}" Width="250" />
                </StackPanel>
            </StackPanel>
            <StackPanel Orientation="Horizontal" Margin="0,5" HorizontalAlignment="Center"
                        VerticalAlignment="Bottom"
                        DockPanel.Dock="Bottom">
                <Button Name="btnSave" Width="100" Height="40"
                        cal:Message.Attach="SaveStudent">
                    <TextBlock Text="Save" FontSize="15" />
                </Button>
            </StackPanel>
        </DockPanel>
    </Grid>
</UserControl>

VIEWMODEL：

public class StudentViewModel : PropertyChangedBase
{
    public StudentModel Student { get; set; }

    public String StudentName
    {
        get { return Student.FirstName; }
        set
        {
            Student.FirstName = value;
            NotifyOfPropertyChange(() => Student.FirstName);
        }
    }

    public Double StudentGrade
    {
        get { return Student.GradePoint; }
        set
        {
            Student.GradePoint = value;
            NotifyOfPropertyChange(() => Student.GradePoint);
            NotifyOfPropertyChange(() => CanSaveStudent);
        }
    }

    public void SaveStudent()
    {
        MessageBox.Show(String.Format("Saved: {0} - ({1})", Student.FirstName, Student.GradePoint));
    }

    public StudentViewModel()
    {
        Student = new StudentModel { FirstName = "Tom Johnson", GradePoint = 3.7 };
    }

    public Boolean CanSaveStudent
    {
        get { return Student.GradePoint >= 0.0 && Student.GradePoint <= 4.0; }
    }
}

如何在此代码中添加一个guard属性？

4 个答案: