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?


当前回答

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!

其他回答

首先,您可能对Spinner类的prompt属性感兴趣。如下图所示,“Choose a Planet”是可以用android在XML中设置的提示符:prompt=""。

我建议子类化Spinner,在这里您可以在内部维护两个适配器。一个适配器有“选择一个”选项,另一个真正的适配器(有实际的选项),然后使用OnClickListener在选项对话框显示之前切换适配器。然而,在尝试实现这个想法后,我得出的结论是,你不能接收小部件本身的OnClick事件。

您可以将旋转器包装在不同的视图中,拦截视图上的单击,然后告诉CustomSpinner切换适配器,但这似乎是一种糟糕的hack。

你真的需要显示“选择一”吗?

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。

我昨天遇到了同样的问题,不想向ArrayAdapter添加隐藏项或使用反射,这工作得很好,但有点脏。

在阅读了许多帖子和尝试之后,我通过扩展ArrayAdapter和覆盖getView方法找到了一个解决方案。

import android.content.Context;
import android.support.annotation.NonNull;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;

/**
 * A SpinnerAdapter which does not show the value of the initial selection initially,
 * but an initialText.
 * To use the spinner with initial selection instead call notifyDataSetChanged().
 */
public class SpinnerAdapterWithInitialText<T> extends ArrayAdapter<T> {

    private Context context;
    private int resource;

    private boolean initialTextWasShown = false;
    private String initialText = "Please select";

    /**
     * Constructor
     *
     * @param context The current context.
     * @param resource The resource ID for a layout file containing a TextView to use when
     *                 instantiating views.
     * @param objects The objects to represent in the ListView.
     */
    public SpinnerAdapterWithInitialText(@NonNull Context context, int resource, @NonNull T[] objects) {
        super(context, resource, objects);
        this.context = context;
        this.resource = resource;
    }

    /**
     * Returns whether the user has selected a spinner item, or if still the initial text is shown.
     * @param spinner The spinner the SpinnerAdapterWithInitialText is assigned to.
     * @return true if the user has selected a spinner item, false if not.
     */
    public boolean selectionMade(Spinner spinner) {
        return !((TextView)spinner.getSelectedView()).getText().toString().equals(initialText);
    }

    /**
     * Returns a TextView with the initialText the first time getView is called.
     * So the Spinner has an initialText which does not represent the selected item.
     * To use the spinner with initial selection instead call notifyDataSetChanged(),
     * after assigning the SpinnerAdapterWithInitialText.
     */
    @Override
    public View getView(int position, View recycle, ViewGroup container) {
        if(initialTextWasShown) {
            return super.getView(position, recycle, container);
        } else {
            initialTextWasShown = true;
            LayoutInflater inflater = LayoutInflater.from(context);
            final View view = inflater.inflate(resource, container, false);

            ((TextView) view).setText(initialText);

            return view;
        }
    }
}

Android在初始化Spinner时所做的,是在为T[]对象中的所有项目调用getView之前为所选项目调用getView。 SpinnerAdapterWithInitialText在第一次调用时返回带有initialText的TextView。 其他时间都调用super。getView是ArrayAdapter的getView方法如果你正常使用Spinner,它会被调用。

要找出用户是否选择了一个微调项,或者微调器是否仍然显示initialText,请调用selectionMade并移交适配器分配给的微调器。

如果您在从数据库游标填充项时遇到此问题,

我在这个SO答案中找到的最简单的解决方案:

在游标适配器查询中使用UNION,并将id= -1的附加项添加到查询结果中,而不真正将其添加到DB中:

喜欢的东西:

db.rawQuery("SELECT iWorkerId as _id, nvLastName as name  FROM  Worker
w  UNION  SELECT -1 as _id , '' as name",null);

如果选择的项目是-1,那么它是默认值。否则 这是桌子上的记录。

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;
    }
  }
}