我想使用一个微调器，最初(当用户还没有做出选择时)显示文本“Select One”。当用户单击微调器时，将显示项目列表，用户可以选择其中一个选项。用户做出选择后，所选项目将显示在微调器中，而不是“Select One”。
我有以下代码来创建一个旋转器:
String[] items = new String[] {"One", "Two", "Three"};
Spinner spinner = (Spinner) findViewById(R.id.mySpinner);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, items);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
使用这段代码，最初会显示项目“One”。我可以在项目中添加一个新项目“Select One”，但“Select One”也会作为第一项显示在下拉列表中，这不是我想要的。
我该如何解决这个问题?
我最终使用了Button。虽然Button不是旋转器，但其行为很容易自定义。
首先像往常一样创建适配器:
String[] items = new String[] {"One", "Two", "Three"};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_dropdown_item, items);
注意，我使用simple_spinner_dropdown_item作为布局id。这将有助于创建一个更好的外观时，创建警报对话框。
在onClick处理我的按钮，我有:
public void onClick(View w) {
new AlertDialog.Builder(this)
.setTitle("the prompt")
.setAdapter(adapter, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// TODO: user specific action
dialog.dismiss();
}
}).create().show();
}
就是这样!
我得到了同样的问题旋转，与一个空的选择，我找到了一个更好的解决方案。看看这段简单的代码。
Spinner lCreditOrDebit = (Spinner)lCardPayView.findViewById(R.id.CARD_TYPE);
spinneradapter lAdapter =
new spinneradapter(
BillPayScreen.this,
ndroid.R.layout.simple_spinner_item,getResources().getStringArray(R.array.creditordebit));
lAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
lCreditOrDebit.setAdapter(lAdapter);
这里spinneradapter是对arrayadapter的一个小定制。它是这样的:
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
public class spinneradapter extends ArrayAdapter<String>{
private Context m_cContext;
public spinneradapter(Context context,int textViewResourceId, String[] objects) {
super(context, textViewResourceId, objects);
this.m_cContext = context;
}
boolean firsttime = true;
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(firsttime){
firsttime = false;
//Just return some empty view
return new ImageView(m_cContext);
}
//Let the array adapter take care of it this time.
return super.getView(position, convertView, parent);
}
}
对于那些使用Xamarin的人，下面是与上面aaronvargas的答案相当的c#版本。
using Android.Content;
using Android.Database;
using Android.Views;
using Android.Widget;
using Java.Lang;
namespace MyNamespace.Droid
{
public class NothingSelectedSpinnerAdapter : BaseAdapter, ISpinnerAdapter, IListAdapter
{
protected static readonly int EXTRA = 1;
protected ISpinnerAdapter adapter;
protected Context context;
protected int nothingSelectedLayout;
protected int nothingSelectedDropdownLayout;
protected LayoutInflater layoutInflater;
public NothingSelectedSpinnerAdapter(ISpinnerAdapter spinnerAdapter, int nothingSelectedLayout, Context context) : this(spinnerAdapter, nothingSelectedLayout, -1, context)
{
}
public NothingSelectedSpinnerAdapter(ISpinnerAdapter spinnerAdapter, int nothingSelectedLayout, int nothingSelectedDropdownLayout, Context context)
{
this.adapter = spinnerAdapter;
this.context = context;
this.nothingSelectedLayout = nothingSelectedLayout;
this.nothingSelectedDropdownLayout = nothingSelectedDropdownLayout;
layoutInflater = LayoutInflater.From(context);
}
protected View GetNothingSelectedView(ViewGroup parent)
{
return layoutInflater.Inflate(nothingSelectedLayout, parent, false);
}
protected View GetNothingSelectedDropdownView(ViewGroup parent)
{
return layoutInflater.Inflate(nothingSelectedDropdownLayout, parent, false);
}
public override Object GetItem(int position)
{
return position == 0 ? null : adapter.GetItem(position - EXTRA);
}
public override long GetItemId(int position)
{
return position >= EXTRA ? adapter.GetItemId(position - EXTRA) : position - EXTRA;
}
public override View GetView(int position, View convertView, ViewGroup parent)
{
// This provides the View for the Selected Item in the Spinner, not
// the dropdown (unless dropdownView is not set).
if (position == 0)
{
return GetNothingSelectedView(parent);
}
// Could re-use the convertView if possible.
return this.adapter.GetView(position - EXTRA, null, parent);
}
public override int Count
{
get
{
int count = this.adapter.Count;
return count == 0 ? 0 : count + EXTRA;
}
}
public override View GetDropDownView(int position, View convertView, ViewGroup parent)
{
// Android BUG! http://code.google.com/p/android/issues/detail?id=17128 -
// Spinner does not support multiple view types
if (position == 0)
{
return nothingSelectedDropdownLayout == -1 ?
new View(context) :
GetNothingSelectedDropdownView(parent);
}
// Could re-use the convertView if possible, use setTag...
return adapter.GetDropDownView(position - EXTRA, null, parent);
}
public override int GetItemViewType(int position)
{
return 0;
}
public override int ViewTypeCount => 1;
public override bool HasStableIds => this.adapter.HasStableIds;
public override bool IsEmpty => this.adapter.IsEmpty;
public override void RegisterDataSetObserver(DataSetObserver observer)
{
adapter.RegisterDataSetObserver(observer);
}
public override void UnregisterDataSetObserver(DataSetObserver observer)
{
adapter.UnregisterDataSetObserver(observer);
}
public override bool AreAllItemsEnabled()
{
return false;
}
public override bool IsEnabled(int position)
{
return position > 0;
}
}
}
最好的解决方案，我发现这实际上不是使用一个纺纱机，而是一个AutoCompleteTextView。它基本上是一个带有附加Spinner的EditText，可以在你输入时显示建议-但是，通过正确的配置，它可以完全按照OP的要求进行操作。
XML:
<com.google.android.material.textfield.TextInputLayout
android:id="@+id/item"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<androidx.appcompat.widget.AppCompatAutoCompleteTextView
android:id="@+id/input"
android:hint="Select one"
style="@style/AutoCompleteTextViewDropDown"/>
</com.google.android.material.textfield.TextInputLayout>
风格:
<style name="AutoCompleteTextViewDropDown">
<item name="android:clickable">false</item>
<item name="android:cursorVisible">false</item>
<item name="android:focusable">false</item>
<item name="android:focusableInTouchMode">false</item>
<item name="android:layout_width">match_parent</item>
<item name="android:layout_height">wrap_content</item>
</style>
至于适配器，使用基本的ArrayAdapter或扩展它来创建自己的适配器，但不需要在适配器方面进行额外的定制。在AutoCompleteTextView上设置适配器。
