让我解释一下我的情况.我有wpf用户控件,可以动态生成组合框.为此,我使用类Control Service,从中创建带有组合框项目的组合框,并管理每个组合框的选择更改事件.
在我尝试在第一个组合框上举起第二个事件之前,一切工作都很好.当我尝试清除第二个组合框的项目时出现问题.我做了debubugg,我已经检查过的组合框引用没有问题(childCmB!= null),但是在尝试清除此组合框的项目之后.引发异常.
我尝试在论坛上找到许多案例,但都取得了成功,因此,我希望能提供任何解决此问题的建议.
谢谢
ControlService.class:
static class ControlService
{
private static ObservableDictionary<String, System.Windows.UIElement> controls = new ObservableDictionary<String, System.Windows.UIElement>();
private static Grid expanderContent;
public static Expander createExpander(String header, String name, String code)
{
header = manageControlName(header);
ExpanderModelView expanderModelView = new ExpanderModelView(name);
//Recieve template grid
expanderContent = expanderModelView.getExpanderContent();
//Add in static collection
Expander expander = new Expander() { Header = header };
//Code of provider service
expander.Uid = code;
expander.Name = name;
//Set up handler
expanderContent.AddHandler(System.Windows.Controls.ComboBox.SelectionChangedEvent, new SelectionChangedEventHandler(cmb_SelectionChanged));
//Insert data
expander.Content = expanderContent;
controls.Add(header, expander);
return expander;
}
public static void cleanUIElementCollection()
{
controls.Clear();
}
private static string manageControlName(string name)
{
int counter = 1;
if (controls.Count != 0)
{
foreach (String value in controls.Keys)
{
if (value.Equals(name))
{
if (name.Any(char.IsDigit))
name = name.Substring(0, name.IndexOf("("));
name = String.Format(name + "({0})", counter);
counter++;
}
}
}
return name;
}
private static void cmb_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
Grid currentContent = sender as Grid;
String selectedItemId = ((e.Source as System.Windows.Controls.ComboBox).SelectedItem as ComboBoxItem).Uid;
IEnumerable<Parameter> childCmBs = DataService.getServiceParametersByParentId((e.Source as System.Windows.Controls.ComboBox).Uid);
if (childCmBs.Any())
{
foreach (Parameter param in childCmBs)
{
try
{
System.Windows.Controls.ComboBox childCmB = currentContent.FindName(param.Key) as System.Windows.Controls.ComboBox;
if (childCmB != null)
{
childCmB.Items.Clear();
addComboBoxItems(DataService.getChildrenParameterValuesByParentId(selectedItemId), childCmB);
}
}
catch (Exception ex)
{
System.Windows.MessageBox.Show(String.Format("Happen some problem during creating comboboxes: {0}", ex.Message));
}
}
}
}
public static void createComboBoxes(IEnumerable<Parameter> parameters, System.Windows.Controls.Panel panel)
{
foreach (Parameter parameter in parameters)
{
TextBlock cmbLabel = new TextBlock() { Text = parameter.Caption };
System.Windows.Controls.ComboBox cmb = new System.Windows.Controls.ComboBox() { Name = parameter.Key, Uid = parameter.ID };
panel.Children.Add(cmbLabel);
panel.Children.Add(cmb);
addComboBoxItems(parameter.ParameterValue, cmb);
}
}
public static void addComboBoxItems(IEnumerable<ParameterValue> parameterValues, System.Windows.Controls.ComboBox cmb)
{
foreach (ParameterValue value in parameterValues)
{
ComboBoxItem item = new ComboBoxItem()
{
Content = value.Caption,
Uid = value.ID,
Name = value.Key
};
cmb.Items.Add(item);
}
}
}
解决方法:
我不确定,但我认为问题是此行:
String selectedItemId = ((e.Source as System.Windows.Controls.ComboBox).SelectedItem as ComboBoxItem).Uid;
当您清除组合框的项目时,
e.Source为System.Windows.Controls.ComboBox).SelectedItem作为ComboBoxItem)为null.
因此,当您尝试获取空项目的Uid时,它将引发异常.