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?
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;
}
}
}
对此，我找到了很多好的解决方案。大多数是通过在适配器的末尾添加一个项来工作的，并且不在下拉列表中显示最后一个项。
对我来说最大的问题是旋转器下拉列表将从列表的底部开始。所以用户看到的最后一个项目，而不是第一个项目(在情况下有许多项目显示)，触摸转轮后，第一次。
所以我把提示项放在列表的开头。并在下拉列表中隐藏第一项。
private void loadSpinner(){
HintArrayAdapter hintAdapter = new HintArrayAdapter<String>(context, 0);
hintAdapter.add("Hint to be displayed");
hintAdapter.add("Item 1");
hintAdapter.add("Item 2");
.
.
hintAdapter.add("Item 30");
spinner1.setAdapter(hintAdapter);
//spinner1.setSelection(0); //display hint. Actually you can ignore it, because the default is already 0
//spinner1.setSelection(0, false); //use this if don't want to onItemClick called for the hint
spinner1.setOnItemSelectedListener(yourListener);
}
private class HintArrayAdapter<T> extends ArrayAdapter<T> {
Context mContext;
public HintArrayAdapter(Context context, int resource) {
super(context, resource);
this.mContext = context
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(android.R.layout.simple_spinner_item, parent, false);
TextView texview = (TextView) view.findViewById(android.R.id.text1);
if(position == 0) {
texview.setText("");
texview.setHint(getItem(position).toString()); //"Hint to be displayed"
} else {
texview.setText(getItem(position).toString());
}
return view;
}
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
View view;
if(position == 0){
view = inflater.inflate(R.layout.spinner_hint_list_item_layout, parent, false); // Hide first row
} else {
view = inflater.inflate(android.R.layout.simple_spinner_dropdown_item, parent, false);
TextView texview = (TextView) view.findViewById(android.R.id.text1);
texview.setText(getItem(position).toString());
}
return view;
}
}
在@Override getDropDownView()中设置下面的布局，当position为0时，隐藏第一个提示行。
R.layout.spinner_hint_list_item_layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
</LinearLayout>
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!
