Question

我正在研究在我的应用程序中动态生成的一组radiobuttons。在访问班级成员时，我似乎面临着一个问题。以下是我到目前为止所做的事情：

XAML：

<GroupBox Header="Daughter Cards" Height="Auto" HorizontalAlignment="Stretch" Margin="20,5,20,20" Name="groupBox2" VerticalAlignment="Stretch" Width="Auto">
            <Grid>                   
                <Grid Grid.Column="0">
                    <ItemsControl ItemsSource="{Binding SlotChildren}">
                        <ItemsControl.ItemsPanel>
                            <ItemsPanelTemplate>
                                <UniformGrid Columns="3" Rows="8" />
                            </ItemsPanelTemplate>
                        </ItemsControl.ItemsPanel>

                        <ItemsControl.ItemTemplate>
                            <DataTemplate>
                                <RadioButton Content="{Binding SlotButtons}" Margin="0,10,0,0" IsChecked="{Binding IsChecked}" GroupName="SlotGroup" Height="15" Width="80" HorizontalAlignment="Center" VerticalAlignment="Center"/>
                            </DataTemplate>
                        </ItemsControl.ItemTemplate>
                    </ItemsControl>
                </Grid>                

                <Grid Grid.Column="1">                                                  
                        <ComboBox Grid.Row="0" ItemsSource="{Binding DaughterBoardBoxList}" SelectedItem="{Binding SelectedDaughterBoardBoxList, Mode=TwoWay}" SelectedIndex="0" Height="23" HorizontalAlignment="Center" Margin="0" Name="comboBox5" VerticalAlignment="Center" Width="158" />
                        <ComboBox Grid.Row="1" ItemsSource="{Binding DaughterVersionBoxList}" SelectedItem="{Binding SelectedDaughterVersionBoxList, Mode=TwoWay}" SelectedIndex="0" Height="23" HorizontalAlignment="Center" Margin="0" Name="comboBox6" VerticalAlignment="Center" Width="158" />
                        <ComboBox Grid.Row="2" ItemsSource="{Binding DaughterSerialBoxList}" SelectedItem="{Binding SelectedDaughterSerialBoxList, Mode=TwoWay}" SelectedIndex="0" Height="23" HorizontalAlignment="Center" Margin="0" Name="comboBox7" VerticalAlignment="Center" Width="158" />

                        <Button Grid.Row="1" Command="{Binding GetStringCommand}" Content="Get String" Height="23" HorizontalAlignment="Center" Margin="0" Name="RefreshDaughterCards" VerticalAlignment="Center" Width="90" />
                        <Button Grid.Row="2" Command="{Binding SetStringCommand}" Content="Set String" Height="23" HorizontalAlignment="Center" Margin="0" Name="WriteEEPROMDCBtn" VerticalAlignment="Center" Width="90" />
                        <Label Content="{Binding DaughterStatus}" Height="25" HorizontalAlignment="Center" Margin="0" Name="DaughterCardLabel" VerticalAlignment="Center" Width="170" />
                    </Grid>                                       
                </Grid> 
        </GroupBox>

EEPROMViewModel类：

public ObservableCollection<EEPROMSlotViewModel> SlotChildren { get; set; }

public EEPROMViewModel ()
{
        SlotChildren = new ObservableCollection<EEPROMSlotViewModel>();
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "0 : None", ID = 0 });
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "1 : None", ID = 1 });
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "2 : None", ID = 2 });
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "3 : None", ID = 3 });
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "4 : None", ID = 4 });
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "5 : None", ID = 5 });
        SlotChildren.Add(new EEPROMSlotViewModel() { ParentVM = this, SlotButtons = "6 : None", ID = 6 });
 }

生成7个与每个相关的ID的单选按钮。

EEPROMSlotViewModel类：

private string _SlotButtons;
    public string SlotButtons
    {
        get; set;
    }

    private EEPROMViewModel _parentVm;
    public EEPROMViewModel ParentVM
    {
        get; set;
    }

    private int _ID;
    public int ID
    {
        get; set;
    }

    private bool _isChecked;
    public bool IsChecked
    {
        get; set;
    }

因此，每当我选择单选按钮并单击SETSTRING按钮时，将执行以下代码：

EEPROMSlotViewModel mSlotVM = new EEPROMSlotViewModel();

        string label;
        if (mSlotVM.ID == 0) //Accessing the 1st radiobutton clicked
        {
            label = string.Empty;
            mSlotVM.getShortName(0, label);
            if (label == string.Empty)
            {
                label = "None";
            }

            mSlotVM.SlotButtons = Convert.ToString(0 + ":" + label); // Setting CONTENT of radiobutton selected 
        }

假设我点击了第一个单选按钮，ID应为0.它调用getShortName()方法执行以下操作：

ParentVM.SelectedDaughterBoardBoxList = ParentVM.DaughterBoardBoxList[0];
ParentVM.SelectedDaughterVersionBoxList = ParentVM.DaughterVersionBoxList[0];
ParentVM.SelectedDaughterSerialBoxList = ParentVM.DaughterSerialBoxList[0];
shortlabel = "Hello";

我在这里遇到的问题很少：

mSlotVM正确访问其他类成员/函数吗？
一旦控件进入getShortname()，它就会抛出以下内容：Object reference not set to an instance of an object. at ParentVM.DaughterBoardBoxList[0];。
即使我在getShortName（）中注释前3个语句，当调用getShortName时，一旦控件返回，值为 label是“”，我应该是“你好”。

我觉得mSlotVm这就是异常背后的原因。请帮助：）

Answer 1

不，您只需创建EEPROMSlotViewModel - 类的新实例，而不是访问任何RadioButtons ViewModel。
如果您能向我们展示您的EEPROMViewModel - 班级会很有帮助。我认为问题是，ParentVM. - 列表为空。

要实现您的目标，您的getShortname() - 方法必须如下所示：

public void getShortname(int i, ref string shortlabel)
{
    ParentVM.SelectedDaughterBoardBoxList = ParentVM.DaughterBoardBoxList[0];
    ParentVM.SelectedDaughterVersionBoxList = ParentVM.DaughterVersionBoxList[0];
    ParentVM.SelectedDaughterSerialBoxList = ParentVM.DaughterSerialBoxList[0];
    shortlabel = "Hello";
}

编辑：通过EEPROMSlotViewModel mSlotVM = new EEPROMSlotViewModel();，您可以创建EEPROMSlotViewModel的新实例，但是您没有获得已检查的RadioButtons ViewModel。所以，当你调用mSlotVM.getShortName(0, label);时，mSlotVM没有ParentVM，这就是引发异常的原因。您可以做的是浏览SlotChildren-List并获取其IsChecked属性为true的EEPROMSlotViewModel。

示例：

EEPROMSlotViewModel checkedVM;    
string label = string.Empty;
foreach (EEPROMSlotViewModel vm in SlotChildren)
{
    if (vm.IsChecked)
    {
        checkedVM = vm;
    }
    else
    {
        vm.SlotButtons = vm.ID + " : NONE"
    }

} 
checkedVM.getShortName(0, ref label);
if (label == string.Empty)
{
    label = "None";
}
checkedVM.SlotButtons = Convert.ToString(0 + ":" + label); // Setting CONTENT of radiobutton selected

无法访问WPF中其他ViewModel类的成员

1 个答案: