Question

我使用项目模板在WF中创建了一个已检查的ListBox。这是xaml代码。

<ListBox.ItemTemplate>
    <DataTemplate x:Name="datatemplate_List">
        <StackPanel x:Name="stackpanel_List" Orientation="Horizontal"  >
            <CheckBox x:Name="checkbox_List" VerticalAlignment="Center" HorizontalAlignment="Left" Width="22"/>
            <Label x:Name="label_List" Height="18" FontSize="12" Padding="0" VerticalContentAlignment="Top" Content="{TemplateBinding ContentPresenter.Content}"/>
        </StackPanel>
    </DataTemplate>
</ListBox.ItemTemplate>

我还有另一个usercontrol，里面有这个已检查的列表框。此usercontrol具有一个属性，用于获取和设置已选中列表框的复选框。 get函数返回所有已检查项的列表，并且此函数正确执行，set函数取消选中列表框中的所有项，然后仅检查值中检查的项。

 public List<string> measurements
    {
        get
        {
            List<string> measList = new List<string>();
            //foreach (string chkBox in chkListBox_Meas.CheckedItems) measList.Add(chkBox); marks code

            for (int i = 0; i < chkListBox_Meas.Items.Count; i++)
            {
                ListBoxItem listBoxItem = (ListBoxItem)(chkListBox_Meas.ItemContainerGenerator.ContainerFromItem(chkListBox_Meas.Items[i]));
                ContentPresenter contentPresenter = FindVisualChild<ContentPresenter>(listBoxItem);
                DataTemplate dataTemplate = contentPresenter.ContentTemplate;
                StackPanel stack = (StackPanel)dataTemplate.FindName("stackpanel_List", contentPresenter);
                CheckBox checkBox = (CheckBox)stack.FindName("checkbox_List");
                Label label = (Label)stack.FindName("label_List");
                if (checkBox.IsChecked == true)
                {
                    measList.Add(label.Content.ToString());
                }
            }
            return measList;
        }

         set
        {

            for (int i = 0; i < chkListBox_Meas.Items.Count; i++)
            {
                ListBoxItem listBoxItem = (ListBoxItem)chkListBox_Meas.ItemContainerGenerator.ContainerFromItem(chkListBox_Meas.Items[i]);
                ContentPresenter contentPresenter = FindVisualChild<ContentPresenter>(listBoxItem);
                DataTemplate dataTemplate = contentPresenter.ContentTemplate;
                StackPanel stack = (StackPanel)dataTemplate.FindName("stackpanel_List", contentPresenter);
                CheckBox checkBox = (CheckBox)stack.FindName("checkbox_List");
                checkBox.IsChecked = false;
            }

            foreach (string meas in value)
            {
                for (int i = 0; i < chkListBox_Meas.Items.Count; i++)
                {

                    ListBoxItem listBoxItem = (ListBoxItem)(chkListBox_Meas.ItemContainerGenerator.ContainerFromItem(chkListBox_Meas.Items[i]));
                    ContentPresenter contentPresenter = FindVisualChild<ContentPresenter>(listBoxItem);
                    DataTemplate dataTemplate = contentPresenter.ContentTemplate;
                    StackPanel stack = (StackPanel)dataTemplate.FindName("stackpanel_List", contentPresenter);
                    CheckBox checkBox = (CheckBox)stack.FindName("checkbox_List");
                    Label label = (Label)stack.FindName("label_List");

                    if (label.Content.ToString() == meas) checkBox.IsChecked = true;
                }
            }
        }
    }

执行此行代码时出现问题。 ListBoxItem listBoxItem = (ListBoxItem chkListBox_Meas.ItemContainerGenerator.ContainerFromItem(chkListBox_Meas.Items[i]);

当在get函数中执行它时，它返回一个listboxitem，如它所假设的那样。但是当在set函数中执行此行时，它返回null。

Answer 1

null返回ItemContainerGenerator值的原因是ListBoxItem listBoxItem = (ListBoxItem)(chkListBox_Meas.ItemContainerGenerator.ContainerFromItem(chkListBox_Meas.Items[i]));行

ItemContainerGenerator.StatusChanged

尚未生成尝试访问权限。

解决方案是调用ContainerGenerated事件处理程序并等待状态更改为ListBoxItem。一旦发生这种情况，您将能够访问Me.Subform.Requery

wpf - ContainerFromItem在set方法中返回null但在get方法中工作正常

1 个答案: