定制问题Xamarin.Forms.ListView

Question

定制Xamarin.Forms.ListView中的问题

任务:我需要实现一个控件显示项目在GridView上的android。

问题的本质并尝试实现它:我创建了类GridListBox继承GridListBox Xamarin.Forms.ListView。接下来我创建了GridListBoxRenderer，例如Xamarin.Forms.Platform.Android.ListViewRenderer

我GridListBox

:

public class GridListBox : ListView
    {
        public static readonly BindableProperty ColumnCountProperty = BindableProperty.Create<GridListBox, int>(r => r.ColumnCount, 2);
        public int ColumnCount
        {
            get { return (int)GetValue(ColumnCountProperty); }
            set { SetValue(ColumnCountProperty, value); }
        }
        public static readonly BindableProperty HorizontalSpacingProperty = BindableProperty.Create<GridListBox, int>(r => r.HorizontalSpacing, 5);
        public int HorizontalSpacing
        {
            get { return (int)GetValue(HorizontalSpacingProperty); }
            set { SetValue(HorizontalSpacingProperty, value); }
        }
        public static readonly BindableProperty VerticalSpacingProperty = BindableProperty.Create<GridListBox, int>(r => r.VerticalSpacing, 5);
        public int VerticalSpacing
        {
            get { return (int)GetValue(VerticalSpacingProperty); }
            set { SetValue(VerticalSpacingProperty, value); }
        }
    }

GridListBox渲染器:

public class GridListBoxRenderer:NativeRenderer
    {
        private Cell cellFocused;
        protected override void OnModelChanged(VisualElement oldModel, VisualElement newModel)
        {
            base.OnModelChanged(oldModel, newModel);
            var realListView = (GridView)Control;
            if (realListView == null)
            {
                realListView = new GridView(Context);
                SetNativeControl((View)realListView);
            }
            cellFocused = (Cell)null;
            realListView.Focusable = false;
            realListView.DescendantFocusability = DescendantFocusability.AfterDescendants;
            realListView.OnFocusChangeListener = (IOnFocusChangeListener)this;
            realListView.SetNumColumns(((Controls.GridListBox) newModel).ColumnCount);
            realListView.SetHorizontalSpacing(((Controls.GridListBox)newModel).HorizontalSpacing);
            realListView.SetVerticalSpacing(((Controls.GridListBox)newModel).VerticalSpacing);
            realListView.Adapter = new GridViewAdapter(Context, realListView, (Controls.GridListBox)newModel);
        }
        public override Size MinimumSize()
        {
            return new Size(40.0, 40.0);
        }
    }

好戏开始了:如果以Xamarin.Forms.Platform.Android为例，实现GridViewAdapter很容易。ListViewAdapter (access as Internal)。实现公共的BaseAdapter。GetView (int position, View convertView, ViewGroup parent) with use ItemTemplate需要访问Xamarin.Forms.ListView。…

注:Xamarin的开发人员计划如何使开发人员能够自定义Xamarin。窗体如果大多数属性具有内部访问…?

P.P.S.定制Xamarin.Forms.Page也有类似的困难。 Xamarin.Forms.Page。InternalChildren属性是internal

Answer 1

解决这个问题的方法是使用反射来访问内部化属性

 public GridViewAdapter(Context context, GridView realListView, GridListBox gridListView)
            {
                _context = context;
                _realListView = realListView;
                _gridListView = gridListView;
                var info = _gridListView.GetType().GetProperty("TemplatedItems", BindingFlags.Instance |
                                BindingFlags.NonPublic |
                                BindingFlags.Public);
                var item = info.GetValue(_gridListView);
                _templatedItemsList = item as IList;
                _templatedItemsINCC = item as INotifyCollectionChanged;
                _templatedItemsINCC.CollectionChanged += _templatedItemsINCC_CollectionChanged;
            }