xamarin android——数据绑定到控件（四）

本文为通过自定义列表适配器定义ListView，以上文为基础，基于ListActivity。

定义列表项布局，包含一个图片显示，标题和描述

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="80dip">
    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <LinearLayout
        android:orientation="vertical"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_marginLeft="10dip"
        android:layout_marginRight="10dip">
        <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <TextView
            android:id="@+id/description"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </LinearLayout>
</LinearLayout>

为了使视图显示数据，必须自定义适配器。ListView每一个列表项显示的是自定义的Model数据，选择继承BaseAdapter<T>，T为自定义Model

model类内容

public class Model
    {
        public string Name {
            get;
            set;
        }

        public string Description {
            get;
            set;
        }

        public int Image {
            get;
            set;
        }
    }

适配器类需要实现两个方法和两个属性：

Count属性、T类型的this 属性、GetItemId方法、GetView方法。

this属性返回指定索引对应的对象数据。

自定义ModelListAdapter代码：

class ModelListAdapter :BaseAdapter<Model>
    {
        public List<Model> Models {
            get;
            set;
        }

        public ModelListAdapter(List<Model> models)
        {
            Models = models;
        }


        #region implemented abstract members of BaseAdapter

        public override long GetItemId (int position)
        {
            return position;
        }

        public override View GetView (int position, View convertView, ViewGroup parent)
        {
　　　　　　  //从数据源中获取当前位置对应的对象
            var item = Models [position];
　　　　　　  //避免重复创建和销毁列表项视图
            if (convertView==null) {
                LayoutInflater inflater = Application.Context.GetSystemService ("layout_inflater") as LayoutInflater;
                convertView = inflater.Inflate (Resource.Layout.CustomItem,null);
            }

            var image = convertView.FindViewById<ImageView> (Resource.Id.image);
            var title = convertView.FindViewById<TextView> (Resource.Id.title);
            var description = convertView.FindViewById<TextView> (Resource.Id.description);

            image.SetImageResource (item.Image);
            title.Text = item.Name;
            description.Text = item.Description;

            return convertView;
        }

        public override int Count {
            get {
                return Models.Count;
            }
        }

        #endregion

        #region implemented abstract members of BaseAdapter

        public override Model this [int index] {
            get {
                return Models [index];
            }
        }

        #endregion


    }

最后一步，将LiatActivity的ListAdapter赋值为我们自定义的适配器

var models = new List<Model>{
                new Model(){ Name="Name",Description="Description",Image = Resource.Drawable.Icon},
                new Model(){ Name="Name",Description="Description",Image = Resource.Drawable.Icon},
                new Model(){ Name="Name",Description="Description",Image = Resource.Drawable.Icon},
                new Model(){ Name="Name",Description="Description",Image = Resource.Drawable.Icon},
                new Model(){ Name="Name",Description="Description",Image = Resource.Drawable.Icon},
                new Model(){ Name="Name",Description="Description",Image = Resource.Drawable.Icon}
            };

            this.ListAdapter = new ModelListAdapter (models);

自定义适配器，我们可以进行更灵活的处理。在GetView方法中执行更多的操作，如果只是进行简单的自定义列表样式，可以通过SimpleAdapter快速完成操作。

IList<IDictionary<string,object>> items = new JavaList<IDictionary<string,object>> ();
            var item1 = new JavaDictionary<string,object> ();
            item1.Add ("name","show name");
            item1.Add("description","description");
            item1.Add ("image",Resource.Drawable.Icon);

            var item2 = new JavaDictionary<string,object> ();
            item2.Add ("name","show name");
            item2.Add("description","description");
            item2.Add ("image",Resource.Drawable.Icon);

            items.Add (item1);
            items.Add (item2);

            this.ListAdapter = new SimpleAdapter (this,items,Resource.Layout.CustomItem,
                new string[]{"name","description","image"},new int[]{Resource.Id.title,Resource.Id.description,Resource.Id.image});

items为定义的数据源k，定义SimpleAdapter传入参数即可。其中string[] 中定义的值必须等于Dictionary中key的值，string[] 和int[] 两个参数表示from string[] to int[]。即每个string[]中的值作为key，取得Dictionary中的值，赋值给int[] 中id所对应的视图。