第三课 Spinner的使用

Spinner的表现形式相当于C#的ComboBox，样子如下图：

但选择项的添加方式相当不一样，必须使用数据适配器，上例子。

Layout——Main.axml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent">

    <TextView

        android:text="Text"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:id="@+id/textView1" />

    <Spinner

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:id="@+id/spinner1" />

</LinearLayout>

Activity1.cs

using System;

using Android.App;

using Android.Content;

using Android.Runtime;

using Android.Views;

using Android.Widget;

using Android.OS;

using Android.Database;

using Android.Provider;

namespace SpinnerSample

{

    [Activity(Label = "SpinnerSample", MainLauncher = true, Icon = "@drawable/icon")]

    public class SpinnerSample : Activity

    {

        private ICursor _BookmarkCursor;

        public ICursor BookmarkCursor

        {

            get

            {

                if (_BookmarkCursor == null)

                {

                    _BookmarkCursor = GetBookmarkCursor();

                }

                return _BookmarkCursor;

            }

            set { _BookmarkCursor = value; }

        }

        public ICursor GetBookmarkCursor()

        {

            return ManagedQuery(Browser.BookmarksUri,

                new string[] { Browser.BookmarkColumns.Title, Browser.BookmarkColumns.Url, Browser.BookmarkColumns.InterfaceConsts.Id },

                null,

                null,

                null);

        }

        protected override void OnCreate(Bundle bundle)

        {

            base.OnCreate(bundle);

            SetContentView(Resource.Layout.Main);

            CreateSpinner();

        }

        int LastSpinnerSelectedPosition;

        public void CreateSpinner()

        {

            LastSpinnerSelectedPosition = 0;

            var TargetSpinner = FindViewById<Spinner>(Resource.Id.spinner1);

            SimpleCursorAdapter SpinnerAdapter = new SimpleCursorAdapter(this,

                Android.Resource.Layout.SimpleSpinnerItem, BookmarkCursor,

                new string[] { Browser.BookmarkColumns.Title },

                new int[] { Android.Resource.Id.Text1 });

            SpinnerAdapter.SetDropDownViewResource(Android.Resource.Layout.SimpleSpinnerDropDownItem);

            TargetSpinner.Adapter = SpinnerAdapter;

            TargetSpinner.Prompt = "Select ...";

            TargetSpinner.ItemSelected += TargetSpinner_ItemSelected;

        }

        void TargetSpinner_ItemSelected(object sender, AdapterView.ItemSelectedEventArgs e)

        {

            var CurSpinner = (Spinner)sender;

            var CurSelectedIndex = CurSpinner.SelectedItemPosition;

            if (LastSpinnerSelectedPosition != CurSelectedIndex)

            {

                ICursor SelectedItem = (ICursor)CurSpinner.SelectedItem;

                var UrlColumnIndex = SelectedItem.GetColumnIndex(Browser.BookmarkColumns.Url);

                TextView tv = FindViewById<TextView>(Resource.Id.textView1);

                tv.Text = SelectedItem.GetString(UrlColumnIndex);

                LastSpinnerSelectedPosition = CurSelectedIndex;

            }

        }

    }

}

运行此程序需要READ_HISTORY_BOOKMARKS权限，设置方式如下图。