使用 MVVM Light 在 Silverlight 中对组合框进行数据绑定的问题

Question

在与 Silverlight 4 + MVVM-Light 工具包中的问题斗争了大约一周之后，在网上搜索但没有成功之后，我想在这里提出我的问题，并希望有人能给我一些提示。

我想展示简化的程序：

我的模型类：

1. Person

   公共类人 { 私有小数_cod_Person；

   公共十进制 Cod_Person
   {
       获取{返回_cod_Person; }
       设置 { _cod_Person = 值; }
   }
   私有字符串_des_Person；
   
   
   公共字符串 Des_Person
   {
       得到{返回_des_Person; }
       设置 { _des_Person = 值; }
   }
   

   }

2. 人员信息

   公共类PersonInfo { 私人小数_cod_person;

   公共十进制 Cod_person
   {
       得到{返回_cod_person; }
       设置 { _cod_person = 值; }
   }
   私有字符串_des_note；
   
   
   公共字符串 Des_note
   {
       得到{返回_des_note; }
       设置 { _des_note = 值; }
   }
   

   }

是我的 ViewModel：

public class PersonViewModel : ViewModelBase
{
    public RelayCommand<Model.PersonInfo> save_Click { get; private set; }

    public PersonViewModel()
    {
        save_Click = new RelayCommand<Model.PersonInfo>(personInfo =>
        {
            SavePerson(personInfo);
        });
        //the content of the combo box is defined
        AllPerson = new ObservableCollection<Model.Person>
        {
            new Model.Person(){
                Cod_Person = 1,
                Des_Person = "Name 1"
            },
            new Model.Person(){
                Cod_Person = 2,
                Des_Person = "Name 2"
            }
        };

        //an empty PersonInfo is created, which the UI will work on
        ChoosenPerson = new Model.PersonInfo();
    }

    private void SavePerson(Model.PersonInfo personInfo)
    {
        //here some safing processing could be done...
        //but is omitted here


        //and here a new PersonInfo is assigned the ChoosenPerson
        ChoosenPerson = new Model.PersonInfo();
    }

    public const string AllPersonPropertyName = "AllPerson";
    private ObservableCollection<Model.Person> _allPersons = null;
    public ObservableCollection<Model.Person> AllPerson
    {
        get
        {
            return _allPersons;
        }

        set
        {
            if (_allPersons == value)
            {
                return;
            }

            var oldValue = _allPersons;
            _allPersons = value;
            RaisePropertyChanged(AllPersonPropertyName, oldValue, value, true);
        }
    }

    public const string ChoosenPersonPropertyName = "ChoosenPerson";
    private Model.PersonInfo _choosenPerson = null;
    public Model.PersonInfo ChoosenPerson
    {
        get
        {
            return _choosenPerson;
        }

        set
        {
            if (_choosenPerson == value)
            {
                return;
            }

            var oldValue = _choosenPerson;
            _choosenPerson = value;

            // Update bindings and broadcast change using GalaSoft.MvvmLight.Messenging
            RaisePropertyChanged(ChoosenPersonPropertyName, oldValue, value, true);
        }
    }
}

在我的视图 (PersonView) 中，我有一个组合框、一个文本框和一个按钮：

<UserControl x:Class="TEST_STACKOVERFLOW.PersonView"
         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"
         mc:Ignorable="d"
         DataContext="{Binding Source={StaticResource Locator}, Path=PersonViewModel.ChoosenPerson}" d:DesignHeight="258" d:DesignWidth="341">
<Grid>
    <ComboBox Height="23" HorizontalAlignment="Left" Margin="84,51,0,0" Name="comboBox1" VerticalAlignment="Top" Width="120" ItemsSource="{Binding Source={StaticResource Locator}, Path=PersonViewModel.AllPerson}" DisplayMemberPath="Des_Person" SelectedValuePath="Cod_Person" SelectedValue="{Binding Path=Cod_person, Mode=TwoWay}" />
    <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="159,199,0,0" Name="button1" VerticalAlignment="Top" Width="75" Command="{Binding Source={StaticResource Locator}, Path=PersonViewModel.save_Click}" CommandParameter="{Binding}" />
    <TextBox Height="23" HorizontalAlignment="Left" Margin="94,107,0,0" Name="textBox1" VerticalAlignment="Top" Width="120" Text="{Binding Path=Des_note, Mode=TwoWay}" />
</Grid>

第一次单击按钮时，一切正常。单击按钮后传递的参数（PersonInfo）包含所选的 ComboBox 值（Cod_person）和插入的文本（Des_note）。在 SavePerson 方法中，一个新的 PersonInfo 实例被分配给 ChoosenPerson 对象。当我第二次单击该按钮时，出现问题。然后，作为单击按钮后的参数，我得到一个 PersonInfo 类的实例，其中包含文本框中正确插入的文本，但作为在组合框中选择的值，我总是得到 0，与我的内容无关在组合框中选择。这个问题发生在我用作类的组合框项目实例的情况下。如果我仅使用字符串值作为组合框项目，则不会出现此问题。但我必须在组合框中使用类的实例。

我希望有人有提示。 谢谢！

PS：

有趣的事实仍然是，当从“ChoosenPerson = new Model.PersonInfo();”更改 ChoosenPerson 的分配时to _choosenPerson = new Model.PersonInfo(); 这意味着通过使用私有成员而不是访问方法进行分配，第二次单击按钮时，值将正确写入按钮的参数中。唯一的问题是上次插入的值没有被删除。它们在第一次单击按钮后显示。但是当通过访问方法分配新的空 ChoosenPerson 时，它们不会显示...... 我无法解释这种行为。谁能帮助我？谢谢。

Answer 1

亚当走在正确的道路上。我会将您的 PersonViewModel 分配给 DataContext，而不是将其分配给 ChoosenPerson。

<UserControl
    x:Class="TEST_STACKOVERFLOW.PersonView"
    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"
    DataContext="{Binding Source={StaticResource Locator}, Path=PersonViewModel}"
    mc:Ignorable="d" d:DesignHeight="258" d:DesignWidth="341">

    <Grid>
        <ComboBox Height="23" HorizontalAlignment="Left" Margin="84,51,0,0" Name="comboBox1" VerticalAlignment="Top" Width="120" ItemsSource="{Binding AllPerson}" DisplayMemberPath="Des_Person" SelectedValuePath="Cod_Person" SelectedItem="{Binding Path=ChoosenPerson, Mode=TwoWay}" />
        <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="159,199,0,0" Name="button1" VerticalAlignment="Top" Width="75" Command="{Binding save_Click}" CommandParameter="{Binding SelectedItem, ElementName=comboBox1}" />
        <TextBox Height="23" HorizontalAlignment="Left" Margin="94,107,0,0" Name="textBox1" VerticalAlignment="Top" Width="120" Text="{Binding ChoosenPerson.Des_Person, Mode=TwoWay}" />
    </Grid>
</UserControl>

我也会完全摆脱 PersonInfo 类。你不需要这门课。您可以直接使用 Person 对象。将引用从 PersonInfo 更改为 Person 类。另外，如果您想清除 ComboBox 中的当前选择，请将 ChoosenPerson 属性设置为 null。不要新建类的实例。 ChoosenPerson 属性必须为 null 或 AllPerson 集合中的对象之一。

public class PersonViewModel : ViewModelBase
{
    public RelayCommand<Person> save_Click { get; private set; }

    public PersonViewModel()
    {
        save_Click = new RelayCommand<Person>(personInfo =>
        {
            SavePerson(personInfo);
        });

        //the content of the combo box is defined
        AllPerson = new ObservableCollection<Person>
        {
            new Person(){
                Cod_Person = 1,
                Des_Person = "Name 1"
            },
            new Person(){
                Cod_Person = 2,
                Des_Person = "Name 2"
            }
        };

        //an empty PersonInfo is created, which the UI will work on
        ChoosenPerson = new Person();
    }

    private void SavePerson(Person personInfo)
    {
        //here some safing processing could be done...
        //but is omitted here


        //and here a new PersonInfo is assigned the ChoosenPerson
        ChoosenPerson = null;
    }

    public const string AllPersonPropertyName = "AllPerson";
    private ObservableCollection<Person> _allPersons = null;
    public ObservableCollection<Person> AllPerson
    {
        get
        {
            return _allPersons;
        }

        set
        {
            if (_allPersons == value)
            {
                return;
            }

            var oldValue = _allPersons;
            _allPersons = value;
            RaisePropertyChanged(AllPersonPropertyName, oldValue, value, true);
        }
    }

    public const string ChoosenPersonPropertyName = "ChoosenPerson";
    private Person _choosenPerson = null;
    public Person ChoosenPerson
    {
        get
        {
            return _choosenPerson;
        }

        set
        {
            if (_choosenPerson == value)
            {
                return;
            }

            var oldValue = _choosenPerson;
            _choosenPerson = value;

            // Update bindings and broadcast change using GalaSoft.MvvmLight.Messenging
            RaisePropertyChanged(ChoosenPersonPropertyName, oldValue, value, true);
        }
    }
}

Answer 2

我想你想要这样的东西：

<UserControl x:Class="TEST_STACKOVERFLOW.PersonView" 
         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" 
         mc:Ignorable="d" 
         DataContext="{Binding Source={StaticResource Locator}, Path=PersonViewModel}" d:DesignHeight="258" d:DesignWidth="341"> 
<Grid> 
    <ComboBox Height="23" HorizontalAlignment="Left" Margin="84,51,0,0" Name="comboBox1" VerticalAlignment="Top" Width="120" ItemsSource="{Binding AllPerson}" DisplayMemberPath="Des_Person" SelectedValuePath="Cod_Person" SelectedValue="{Binding Path=ChoosenPerson, Mode=TwoWay}" /> 
    <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="159,199,0,0" Name="button1" VerticalAlignment="Top" Width="75" Command="{Binding save_Click}" CommandParameter="{Binding ChoosenPerson}" /> 
    <TextBox Height="23" HorizontalAlignment="Left" Margin="94,107,0,0" Name="textBox1" VerticalAlignment="Top" Width="120" Text="{Binding Path=Des_note, Mode=TwoWay}" /> 
</Grid>

我更新了大部分绑定。一旦设置了 UserControl 的数据上下文，内部的其余控件就可以简单地引用属性名称，而不必使用定位器。我还认为你有一些事情指向了错误的地方。