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?
private boolean isFirst = true;
private void setAdapter() {
final ArrayList<String> spinnerArray = new ArrayList<String>();
spinnerArray.add("Select your option");
spinnerArray.add("Option 1");
spinnerArray.add("Option 2");
spin.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {
TextView tv = (TextView)selectedItemView;
String res = tv.getText().toString().trim();
if (res.equals("Option 1")) {
//do Something
} else if (res.equals("Option 2")) {
//do Something else
}
}
@Override
public void onNothingSelected(AdapterView<?> parentView) { }
});
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.my_spinner_style,spinnerArray) {
public View getView(int position, View convertView, ViewGroup parent) {
View v = super.getView(position, convertView, parent);
int height = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 25, getResources().getDisplayMetrics());
((TextView) v).setTypeface(tf2);
((TextView) v).getLayoutParams().height = height;
((TextView) v).setGravity(Gravity.CENTER);
((TextView) v).setTextSize(TypedValue.COMPLEX_UNIT_SP, 19);
((TextView) v).setTextColor(Color.WHITE);
return v;
}
public View getDropDownView(int position, View convertView,
ViewGroup parent) {
if (isFirst) {
isFirst = false;
spinnerArray.remove(0);
}
View v = super.getDropDownView(position, convertView, parent);
((TextView) v).setTextColor(Color.argb(255, 70, 70, 70));
((TextView) v).setTypeface(tf2);
((TextView) v).setGravity(Gravity.CENTER);
return v;
}
};
spin.setAdapter(adapter);
}
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;
}
}
}
