Question

我正在构建一个需要动态生成和绑定Spinner控件的跨平台应用程序。我能够在iOS和Windows平台上实现这一点，但是在Android方面存在问题。如果我理解正确，我必须将一些参数传递给 MvxSpinner 的构造函数 - context和attrs，但我无法弄清楚我该怎么做以及应该在那里传递什么。另外，我不知道如何绑定ItemsSource和SelectedItem。我想必须创建一个新的绑定集（类似于iOS版本），但我无法在Android上找到它。你能告诉我一些指示吗？

以下是我的Windows版源代码：

private void InputColourAtlasChangedMessageHandler( InputColourAtlasChangedMessage message )
{
    ColourAtlas selected = message.SelectedColourAtlas;
    var vm = ViewModel as ColorMatchViewModel;

    List<ComboBox> newComboboxes = new List<ComboBox>();
    var currentCount = ColourPickersContainer.Children.Count;
    for ( int i = currentCount; i < message.ColourCodePartCount; i++ )
    {
        ComboBox cb = new ComboBox { Margin = new Thickness( 0, 0, 10, 0 ), PlaceholderText = "choose" };
        Binding itemsSourceBinding = new Binding();
        itemsSourceBinding.Path = new PropertyPath( "ColourPartLists[" + i + "]" );
        Binding selectedItemBinding = new Binding();
        selectedItemBinding.Path = new PropertyPath( "SelectedColourCodeParts[" + i + "]" );
        selectedItemBinding.Mode = BindingMode.TwoWay;
        cb.Tag = i;
        ColourPickersContainer.Children.Add( cb );
        cb.SetBinding( ComboBox.ItemsSourceProperty, itemsSourceBinding );
        cb.SetBinding( ComboBox.SelectedItemProperty, selectedItemBinding );
        cb.SelectionChanged += cb_SelectionChanged;                                
        BindingOperations.SetBinding( cb, ComboBox.SelectedItemProperty, selectedItemBinding );
        newComboboxes.Add( cb );
    }
    while ( ColourPickersContainer.Children.Count > message.ColourCodePartCount )
    {
        ColourPickersContainer.Children.RemoveAt( ColourPickersContainer.Children.Count - 1 );
    }
    _comboboxes = newComboboxes;            
}

void cb_SelectionChanged( object sender, SelectionChangedEventArgs e )
{
    var cb = sender as ComboBox;
    int changedIndex = ( int )cb.Tag;
    if ( e.AddedItems.Count > 0 )
    {
        ( DataContext as ColorMatchViewModel ).ColourCodePartChangedCommand.Execute( changedIndex );
    }
}

这是iOS版本（或多或少做同样的事情 - 虽然它只是清除现有的微调器而不是重复使用它们）：

private void InputColourAtlasChangedMessageHandler( InputColourAtlasChangedMessage message )
{
    ColourAtlas selected = message.SelectedColourAtlas;
    ClearPickers();
    var currentSet = this.CreateBindingSet<ColorMatchView, ColorMatchViewModel>();
    for ( int i = 0; i < message.ColourCodePartCount; i++ )
    {
        var j = i;
        UIPickerView picker = new UIPickerView();
        var pickerViewModel = new MvxPickerViewModel( picker );
        picker.Model = pickerViewModel;
        picker.ShowSelectionIndicator = true;
        pickerViewModel.SelectedItemChanged += vm_SelectedItemChanged;
        var textView = new PaddedUITextField( new RectangleF( 10, 50 + i * 40, 300, 30 ) );
        Add( textView );
        textView.InputView = picker;
        _pickers.Add( picker );
        _textViews.Add( textView );
        currentSet.Bind( textView ).For( t => t.Text ).To( "SelectedColourCodeParts[" + i + "]" );
        currentSet.Bind( pickerViewModel ).For( p => p.ItemsSource ).To( "ColourPartLists[" + i + "]" );
        currentSet.Bind( pickerViewModel ).For( p => p.SelectedItem ).To( "SelectedColourCodeParts[" + i + "]" );
        currentSet.Bind( pickerViewModel ).For( p => p.SelectedChangedCommand ).To( vm => vm.ColourCodePartChangedCommand ).CommandParameter( j );
    }
    currentSet.Apply();
    UpdateLayout( View.Frame.Size );
}

private void ClearPickers()
{
    foreach ( var picker in _pickers )
    {
        var vm = picker.Model as MvxPickerViewModel;
        vm.SelectedItemChanged -= vm_SelectedItemChanged;
        picker.RemoveFromSuperview();
    }
    foreach ( var textView in _textViews )
    {
        textView.RemoveFromSuperview();
    }
    _pickers.Clear();
    _textViews.Clear();
}

我现在拥有的Android版本的部分（而非功能）大纲如下：

private void InputColourAtlasChangedMessageHandler( InputColourAtlasChangedMessage message )
        {
            ColourAtlas selected = message.SelectedColourAtlas;
            var layout = FindViewById<LinearLayout>( Resource.Id.spinnerList );
            ClearPickers();

            for ( int i = 0; i < message.ColourCodePartCount; i++ )
            {
                MvxSpinner spinner = new MvxSpinner( Context??, Attrs??);
                MvxAdapter adapter = new MvxAdapter( this );

                spinner.ItemSelected += spinner_ItemSelected;
                layout.AddView( spinner );
                _spinners.Add( spinner );
            }
        }

        void spinner_ItemSelected( object sender, AdapterView.ItemSelectedEventArgs e )
        {
            var changedIndex = _spinners.IndexOf( sender as MvxSpinner );
            ( DataContext as ColorMatchViewModel ).ColourCodePartChangedCommand.Execute( changedIndex );
        }

        private void ClearPickers()
        {
            var layout = FindViewById<LinearLayout>( Resource.Id.spinnerList );
            foreach ( var spinner in _spinners )
            {
                spinner.ItemSelected -= spinner_ItemSelected;
            }
            layout.RemoveAllViews();
            _spinners.Clear();
        }

Answer 1

以下是有关如何通过Activity.OnCreate中的代码创建mvxspinner的示例：

_bindingContext = new MvxAndroidBindingContext(this, new LayoutInflaterProvider(LayoutInflater), _viewModel);
var view = (LinearLayout)_bindingContext.BindingInflate(Resource.Layout.Main, null);
SetContentView(view);
var spinner = new MvxSpinner(this, null, new MvxAdapter(this, _bindingContext));
view.AddView(spinner);

然后，如果您希望LayoutInflaterProvider看起来像这样：

public class LayoutInflaterProvider
    : IMvxLayoutInflater
{
    public LayoutInflaterProvider(LayoutInflater layoutInflater)
    {
        LayoutInflater = layoutInflater;
    }

    public LayoutInflater LayoutInflater { get; private set; }
}

我最初看这个tutorial。

以编程方式在MvvmCross

1 个答案: