如何将ViewModel与CheckBoxes双向绑定？

Question

I have a user admin tool that edits permissions for users. I have the admin select checkboxes at the application.

The permissions can be different from server to server. Right now I just have static checkboxes and its real nasty.

I'm trying to figure out how to create some kind of dynamic scheme for the checkboxes and track when they have been checked / unchecked.

When the user selects the checkboxes I could just search through the object and make the changes to the database.

Well at least that's the way I have thought of it so far. Does anyone have any input or maybe an example of something like this in action ?

Thanks in Advance!

Answer 1

Just use an ItemsControl , bind its ItemsSource to a collection of VMs which represent a permission. In the ItemTemplate you can create a CheckBox whose IsChecked is bound to a property on your item VM which represents the state of that permission.

You then can get all the states from the source collection's objects.

Answer 2

Let's assume there are the following user permissions:

[Flags]
public enum UserPermissions
{
    Administrator = 0x1,
    BackupOperator = 0x2,
    PowerUser = 0x4,
    User = 0x8,
    Guest = 0x10
}

Enum members should be data bound to the checkboxes.

Okay, it will be ListBox with CheckBox items:

1) CheckBox class has boolean IsChecked property, but it can't be bound directly to flags enumeration.

2) ListBox class has ItemsSource property which can be bound to collection.

So, it is necessary to convert the flags enumeration to List of flag ViewModels:

1) Create ViewModel which represents single flag. Let's call it UserPermissionViewModel class. It should have IsChecked boolean and the single enum flag value Permission properties.

public class UserPermissionViewModel : ViewModelBase
{
    public UserPermissionViewModel(UserPermissions permission, bool isSet)
    {
        Permission = permission;
        IsSet = isSet;
    }

    public UserPermissions Permission { get; private set; }

    public bool IsSet { get; set; }
}

2) Create ViewModel for all flags (contains many instances of UserPermissionViewModel class). Let's call it UserPermissionsViewModel class. This ViewModel should take the source enum in constructor and convert it to internal collection of its flags representation: collection of UserPermissionViewModel instances. Also there should be Result property which will return the flags enum using IsChecked property values of UserPermissionViewModel instances.

public class UserPermissionsViewModel
{
    public UserPermissionsViewModel(UserPermissions permissions)
    {
        // Convert each flag of UserPermissions enum to UserPermissionViewModel and pass IsSet (true) if the permissions has the flag.
        Permissions = allPermissions.Select(singlePermission => new UserPermissionViewModel(singlePermission, permissions.HasFlag(singlePermission))).ToList();
    }

    public List<UserPermissionViewModel> Permissions
    {
        get;
        private set;
    }

    public UserPermissions Result
    {
        get
        {
            // Iterate over Permissions list and get result flags enum.
        }
    }

3) Create ListBox in the View, bind it to permission list property of UserPermissionsViewModel class. ListBox should contain CheckBox and TextBlock as ItemTemplate . Bind them to IsChecked and Permission properties accordingly.

After that, the binding should work, the result can be taken using Result property.

<ListBox ItemsSource="{Binding Path=PermissionsViewModel.Permissions}">
  <ListBox.ItemTemplate>
    <DataTemplate>
      <WrapPanel>
        <CheckBox IsChecked="{Binding Path=IsSet}" />
        <TextBlock VerticalAlignment="Center" Text="{Binding Path=Permission}" />
      </WrapPanel>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>

Answer 3

I don't have any code, but maybe some variations you could use:

• Create a set of check boxes and make them visible/invisible as you need them. Preferably if you only have a max. fixed amount.

• Create a list of check boxes, create them dynamically and set an observer (event) to listen to changes (IsChecked).

• Don't use checkboxes but a listview or listbox with checkboxes.

Answer 4

An example of what HB says above:

    <ItemsControl ItemsSource="{Binding Privileges}">
        <ItemsControl .ItemTemplate>
            <DataTemplate DataType="{x:Type Privilege}">
                <StackPanel>
                    <TextBlock Text="{Binding Name}"/>
                    <CheckBox IsChecked="{Binding IsEnabled}"/>
                </StackPanel>
            </DataTemplate>
        </ItemsControl .ItemTemplate>
    </ItemsControl >