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;
}
}
}
XML文件:
<Spinner android:id="@+id/locationSpinner"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:prompt="@string/select_location" />
活动:
private Spinner featuresSelection;
private ArrayAdapter<CharSequence> featuresAdapter;
private List<CharSequence> featuresList;
onCreate:
featuresList = new ArrayList<CharSequence>();
featuresAdapter = new ArrayAdapter<CharSequence>(this,
android.R.layout.simple_spinner_item, featuresList);
featuresAdapter.setDropDownViewResource(
android.R.layout.simple_spinner_dropdown_item);
featuresSelection = ((Spinner) yourActivity.this
.findViewById(R.id.locationSpinner));
featuresSelection.setAdapter(featuresAdapter);
featuresSelection.setOnItemSelectedListener(
new MyOnItemSelectedListener());
某些函数(以编程方式向适配器添加内容)>
featuresAdapter.add("some string");
现在你有一个空的转轮，你可以写代码不打开对话框，如果是空的。或者他们可以反击。但是您也可以在运行时用函数或另一个列表填充它。
String[] listAges = getResources().getStringArray(R.array.ages);
// Creating adapter for spinner
ArrayAdapter<String> dataAdapter =
new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, listAges);
// Drop down layout style - list view with radio button
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// attaching data adapter to spinner
spinner_age.getBackground().setColorFilter(ContextCompat.getColor(this, R.color.spinner_icon), PorterDuff.Mode.SRC_ATOP);
spinner_age.setAdapter(dataAdapter);
spinner_age.setSelection(0);
spinner_age.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String item = parent.getItemAtPosition(position).toString();
if(position > 0){
// get spinner value
Toast.makeText(parent.getContext(), "Age..." + item, Toast.LENGTH_SHORT).show();
}else{
// show toast select gender
Toast.makeText(parent.getContext(), "none" + item, Toast.LENGTH_SHORT).show();
}
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
参考上述答案之一:https://stackoverflow.com/a/23005376/1312796
我添加了我的代码来修复一个小错误。哪里没有数据检索..如何显示提示文本..!
这是我的诀窍……我觉得挺好用的。！
试着把你的旋转器在一个relative_layout和对齐的Textview与你的旋转器和发挥Textview的可见性(SHOW/HIDE)每当旋转器的适配器加载或空..像这样:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:layout_marginTop="20dp"
android:background="#ededed"
android:orientation="vertical">
<TextView
android:id="@+id/txt_prompt_from"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:textColor="@color/gray"
android:textSize="16sp"
android:layout_alignStart="@+id/sp_from"
android:text="From"
android:visibility="gone"/>
<Spinner
android:id="@+id/sp_from"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
/>
代码如下:
txt_from = (TextView) rootView.findViewById(R.id.txt_prompt_from);
在转轮适配器加载并为空前后调用此方法。
setPromptTextViewVisibility ();//正确或错误
setPromptTextViewVisibility (boolean visible)
｛
如果(可见的)
｛
txt_from.setVisibility (View.VISIBLE);
｝
其他的
｛
txt_from.setVisibility (View.INVISIBLE);
｝
｝
