ComboBox WPF中的复选框

Question

您是谁在WPF中的组合框中实现复选框的。

Answer 1

Yes, this is possible. I have done something similar with the ListView which is essentially the same control. The trick here is to make it FAST . It should not take 30 seconds or whatever if you have thousands of items.

Now, how you implement it depends if you want to build a generic control or one specifically for this object type. The reason being is that to do this fast, you need to know which property of the item object is the IsChecked. In my control, I created a DP called IsCheckedPath so its in the spirit of WPF. The control would then auto bind the IsCheckedPath property of each object to the corresponding checkbox.

When the master check box is toggled, you need to loop through the Items and set the property value. You have 2 choices for that: 1) reflection or 2) compile an expression tree upon setting the IsCheckedPath DP.

I did #2 since reflection will be too slow.

If you only care about this specific object and don't think you'll ever reuse the control, then you can skip both and just set the property. Not a good idea IMO, I'd go the generic route :).

Also, note, you can't take a "shortcut" and loop through the visuals and set the checkbox from the other side since WPF controls virtualize and check boxes will not be "alive" for items that are scrolled out of view.

Answer 2

Hello and welcome to WPF! For this situation, it looks like a MultiBinding is what you're looking for. Since the master checkbox can change the individual checkboxes and vice-versa, the binding should be two-way. The MultiBinding would be applied to the master check box, like this:

<Checkbox x:Name="MasterCheckBox">
<Checkbox.IsChecked>
    <MultiBinding Converter="[Instance of your converter class]" Mode="TwoWay">
        <Binding Source="ConversationViewModel.ConversationValues" Convert="{StaticResource PersonFilterTypeToBoolConverter}" ConverterParameter="{x:Static shared:MethodType.Mobile}"/>
        <Binding Source="ConversationViewModel.ConversationValues" Convert="{StaticResource PersonFilterTypeToBoolConverter}" ConverterParameter="{x:Static shared:MethodType.Skype}"/>
        <Binding Source="ConversationViewModel.ConversationValues" Convert="{StaticResource PersonFilterTypeToBoolConverter}" ConverterParameter="{x:Static shared:MethodType.Landline}"/>
    </MultiBinding>
</Checkbox.IsChecked>

You will need to also create a converter. The article linked to above describes how to make a simple converter. In your case, since the binding is two-way, you need to handle both the Convert and ConvertBack methods. The ConvertBack method runs when the master checkbox is changed by the user, so it will have to set all the bindings under the multibinding to true or false. The Convert method runs when one of the individual checkboxes changes. In that case, in WPF, it's proper to set the IsChecked of the master checkbox to true if ALL individual boxes are checked, false if ALL individual boxes are unchecked, and if they are mixed, IsChecked should be null. IsChecked can be null because the type of that property is a bool? (nullable bool), which is how three-state checkboxes work in WPF.