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自定义 Xamarin.Forms.ListView 中的问题

任务：我需要实现一个控件，用于在 GridView 中显示项目，就像在 android 上一样。

问题的本质并尝试实现它：我创建了继承自 GridListBox Xamarin.Forms.ListView 的类 GridListBox。接下来我创建 GridListBoxRenderer 以 Xamarin.Forms.Platform.Android.ListViewRenderer 为例

我的网格列表框：

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 的渲染器：

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);
        }
    }

然后乐趣开始了：如果以Xamarin.Forms.Platform.Android.ListViewAdapter (access as Internal)为例，实现 GridViewAdapter 很容易。要使用 ItemTemplate 实现公共 BaseAdapter.GetView (int position, View convertView, ViewGroup parent) 需要访问Xamarin.Forms.ListView.TemplatedItems 但它是内部的......

PS Xamarin 的开发人员如何计划使开发人员能够自定义 Xamarin.Forms 如果大多数属性具有内部访问权限...？

PPS 自定义 Xamarin.Forms.Page 也有类似的困难。Xamarin.Forms.Page.InternalChildren属性是内部的

4

1 回答 1

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解决这个问题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;
            }
于 2014-07-15T08:47:46.130 回答