一、前言
今天用了一下Spinner这个控件，主要是结合官网的例子来用的，不过官网的是把数据写在Strings.xml中的，
某种程度上，不是很符合我们需要的，比较多的应该都是从数据库读出来，绑定上去的。下面是官网的例子：
https://developer.xamarin.com/guides/android/user_interface/spinner/
二、来个简单的Demo
新建一个类 MyType.cs
1 public class MyType
2 {
3 public int TypeId { get; set; }
4
5 public string TypeName { get; set; }
6
7 public override string ToString()
8 {
9 return TypeId + "-" + TypeName;
10 }
11 }
再来点数据
1 public static class DB
2 {
3 public static List<MyType> Types { get; private set; }
4
5 static DB()
6 {
7 Types = new List<MyType>();
8 Types.Add(new MyType { TypeId = 1, TypeName = "type1" });
9 Types.Add(new MyType { TypeId = 2, TypeName = "type2" });
10 Types.Add(new MyType { TypeId = 3, TypeName = "type3" });
11 Types.Add(new MyType { TypeId = 4, TypeName = "type4" });
12 }
13 }
最后写个Adapter，我们自定义的Adapter都需要继承BaseAdapter
1 public class MyTypeAdapter : BaseAdapter<MyType>
2 {
3 private readonly Activity _context;
4 private readonly IList<MyType> _types;
5
6 public MyTypeAdapter(Activity context, IList<MyType> types)
7 {
8 this._context = context;
9 this._types = types;
10 }
11
12 public override MyType this[int position]
13 {
14 get
15 {
16 return this._types[position];
17 }
18 }
19
20 public override int Count
21 {
22 get
23 {
24 return this._types.Count;
25 }
26 }
27
28 public override long GetItemId(int position)
29 {
30 return position;
31 }
32
33 public override View GetView(int position, View convertView, ViewGroup parent)
34 {
35 View view = convertView;
36 if (view == null)
37 {
38 view = this._context.LayoutInflater.Inflate(Android.Resource.Layout.SimpleListItem1, null);
39 }
40
41 view.FindViewById<TextView>(Android.Resource.Id.Text1).Text = this._types[position].ToString();
42 return view;
43 }
44 }
到这里，会发现有好几个重写的方法！！这些方法是直接通过实现抽象类生成的，然后自己去完善每个方法。
既然都这样了，那就果断去看看这个BaseAdapter是干嘛的
1 //
2 // Summary:
3 // Common base class of common implementation for an Android.Widget.Adapter that
4 // can be /// used in both Android.Widget.ListView (by implementing the specialized
5 // /// Android.Widget.IListAdapter interface} and Android.Widget.Spinner (by implementing
6 // the /// specialized Android.Widget.ISpinnerAdapter interface.
7 //
8 // Type parameters:
9 // T:
10 // To be added.
11 //
12 // Remarks:
13 // ///
14 // Common base class of common implementation for an Android.Widget.Adapter that
15 // can be /// used in both Android.Widget.ListView (by implementing the specialized
16 // /// Android.Widget.IListAdapter interface} and Android.Widget.Spinner (by implementing
17 // the /// specialized Android.Widget.ISpinnerAdapter interface. ///
18 // ///
19 // /// /// [Android Documentation] /// ///
20 // ///
21 [DefaultMember("Item")]
22 [Register("android/widget/BaseAdapter", DoNotGenerateAcw = true)]
23 public abstract class BaseAdapter<T> : BaseAdapter
24 {
25 [Register(".ctor", "()V", "")]
26 public BaseAdapter();
27 public BaseAdapter(IntPtr handle, JniHandleOwnership transfer);
28
29 public abstract T this[int position] { get; }
30
31 public override Java.Lang.Object GetItem(int position);
32 }
可以看到这个主要就是给ListView和Spinner用的。主要的还是它继承了BaseAdapter这个抽象类(下面的，我是去掉了注释的，方便看)
1 public abstract class BaseAdapter : Java.Lang.Object, IListAdapter, ISpinnerAdapter, IAdapter, IJavaObject, IDisposable
2 {
3 public BaseAdapter();
4 protected BaseAdapter(IntPtr javaReference, JniHandleOwnership transfer);
5 public abstract int Count { get; }
6 public virtual bool HasStableIds { get; }
7 public virtual bool IsEmpty { get; }
8 public virtual int ViewTypeCount { get; }
9 protected override IntPtr ThresholdClass { get; }
10 protected override Type ThresholdType { get; }
11 public virtual bool AreAllItemsEnabled();
12 public virtual View GetDropDownView(int position, View convertView, ViewGroup parent);
13 public abstract Java.Lang.Object GetItem(int position);
14 public abstract long GetItemId(int position);
15 public virtual int GetItemViewType(int position);
16 public abstract View GetView(int position, View convertView, ViewGroup parent);
17 public virtual bool IsEnabled(int position);
18 public virtual void NotifyDataSetChanged();
19 public virtual void NotifyDataSetInvalidated();
20 public virtual void RegisterDataSetObserver(DataSetObserver observer);
21 public virtual void UnregisterDataSetObserver(DataSetObserver observer);
22
23 public static class InterfaceConsts
24 {
25 public const int IgnoreItemViewType = -1;
26 public const int NoSelection = int.MinValue;
27 }
28 }
可以看到，我们在自定义Adapter时，自动实现的方法，有好几个是在这里面的！！！
具体每个方法是干嘛的，就看看API吧！
https://developer.xamarin.com/api/type/Android.Widget.BaseAdapter/
下面来看看我们的Activity：
1 [Activity(Label = "SpinnerActivity",MainLauncher =true)]
2 public class SpinnerActivity : Activity
3 {
4 protected override void OnCreate(Bundle savedInstanceState)
5 {
6 base.OnCreate(savedInstanceState);
7
8 // Create your application here
9 SetContentView(Resource.Layout.spinnerlayout);
10
11 var typesSpinner = FindViewById<Spinner>(Resource.Id.typesSpinner);
12
13 typesSpinner.Adapter = new Models.MyTypeAdapter(this, Models.DB.Types);
14
15 typesSpinner.ItemSelected += typesSpinner_ItemSelected;
16 }
17
18 private void typesSpinner_ItemSelected(object sender, AdapterView.ItemSelectedEventArgs e)
19 {
20 Spinner spinner = (Spinner)sender;
21
22 var toast = string.Format(spinner.GetItemAtPosition(e.Position).ToString());
23
24 Toast.MakeText(this, toast, ToastLength.Long).Show();
25 }
26 }
很简单，下面看看效果图
但是呢，我记得在原生的开发中，下面这句应该直接是得到一个Object对象，然后通过强制转化就可以得到对应的Model
spinner.GetItemAtPosition(e.Position)
我试过.net下面的强制转化和object获取在转化，都没办法得到想要的效果
都是这个错。
回想刚才的BaseAdapter类，它继承了Java.Lang.Object
所以就直接让我们的MyType去继承这个试试。可以点出来了！！
再来看看选择后的效果图：
OK，达到想要的效果了！！这样我们就可以得到任何我们想要的属性了！！不用只局限一个.ToString()方法了！
下面是MyType类和typesSpinner_ItemSelected方法
1 public class MyType : Java.Lang.Object
2 {
3 public int TypeId { get; set; }
4
5 public string TypeName { get; set; }
6
7 public override string ToString()
8 {
9 return TypeId + "-" + TypeName;
10 }
11 }
1 private void typesSpinner_ItemSelected(object sender, AdapterView.ItemSelectedEventArgs e)
2 {
3 Spinner spinner = (Spinner)sender;
4
5 //var toast = string.Format(spinner.GetItemAtPosition(e.Position).ToString());
6
7 var toast = (Models.MyType)spinner.GetItemAtPosition(e.Position);
8
9 Toast.MakeText(this, toast.TypeName, ToastLength.Long).Show();
10 }
时间： 2024-08-02 14:46:10