Windows Phone 7-无法从ViewModel触发事件。

Question

I want to write the event for list box from View Model. I try like this:-

 <ListBox.ItemTemplate>
                <DataTemplate>
                    <Border BorderBrush="Gray" Padding="5" BorderThickness="1">
                        <StackPanel Orientation="Horizontal">
                            <Border BorderBrush="Wheat" BorderThickness="1">
                                <Image  Name="ListPersonImage" Source="{Binding PersonImage}" Height="100" Width="100" Stretch="Uniform" Margin="10,0,0,0"/>
                            </Border>
                            <TextBlock Text="{Binding FirstName}" Name="firstName" Width="200" Foreground="White" Margin="10,10,0,0" FontWeight="SemiBold" FontSize="22"  />

                            <Button DataContext="{Binding DataContext, ElementName=listBox1}" Command="{Binding addPerson}" Height="80" Width="80" >
                                <Button.Background>
                                    <ImageBrush  ImageSource="{Binding imagePath,  Converter={StaticResource pathToImageConverter}}" Stretch="Fill" />
                                </Button.Background>
                            </Button>                               
                        </StackPanel>
                    </Border>
                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="Tap">
                            <i:InvokeCommandAction Command="{Binding ItemSelectedCommand,Mode=OneWay}" CommandParameter="{Binding}"/>
                        </i:EventTrigger>
                    </i:Interaction.Triggers>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

My ViewModel:-

  public RelayCommand<MVVMListBoxModel> ItemSelectedCommand { get; private set; }
 public MVVMListBoxViewModel()
        {
           ItemSelectedCommand = new RelayCommand<MVVMListBoxModel>(ItemSelected);
        }

 private void ItemSelected(MVVMListBoxModel myItem)
        {
            MessageBox.Show("Name==>" + myItem.FirstName);
            //throw new NotImplementedException();
        }

But nothing happening. Please let me know where I did mistake. Thanks in advance.

Answer 1

Check output window to see if you got binding error. It seems that you got one, because you have ItemSelectedCommand defined in MVVMListBoxViewModel but ListBoxItem 's DataContext is corresponding MVVMListBoxModel , so binding engine couldn't find the command.

Try to move definition of ItemSelectedCommand to MVVMListBoxModel and see if message box get displayed this way.

Answer 2

Do you want the trigger to be upon the SelectionChanged of the Listbox Item? Then the trigger should be outside the <ListBox.ItemTemplate> ... </ListBox.ItemTemplate> .

And the trigger should bind the CommandParamter to the SelectedItem

<i:Interaction.Triggers>
    <i:EventTrigger EventName="Tap">
        <i:InvokeCommandAction Command="{Binding ItemSelectedCommand,Mode=OneWay}" CommandParameter="{Binding SelectedItem}"/>
     </i:EventTrigger>
</i:Interaction.Triggers>