我正在开发一个跨平台的应用程序，需要动态生成和绑定Spinner控件。我已经在iOS和Windows平台上做到了这一点，但是在Android平台上遇到了问题。如果我理解得正确，我必须向MvxSpinner构造函数传递一些参数 - 上下文和属性，但我不知道如何做到这一点以及应该传递什么。此外，我也不知道如何绑定ItemsSource和SelectedItem。我想应该创建一个新的绑定集（类似于iOS版本），但是我不知道如何在Android上实现。能否给我一些指引呢？
以下是我从Windows版本中提取的源代码：
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 );
}
}
这里是iOS版本（执行的操作基本相同，尽管它只是清除现有的旋转器而不是重用它们）：
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 版本仅有部分（而不是完全）的大纲，具体如下：
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();
}