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

看到答案与轻量级和高可定制的库:

https://stackoverflow.com/a/73085435/6694920

<com.innowisegroup.hintedspinner.HintedSpinner
android:id="@+id/hintedSpinner"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginHorizontal="20dp"
app:hintTextSize="24sp"
app:hintTextColor="@color/red"
app:hint="Custom hint"
app:withDivider="true"
app:dividerColor="@color/dark_green"
app:arrowDrawable="@drawable/example_arrow_4"
app:arrowTint="@color/colorAccent"
app:popupBackground="@color/light_blue"
app:items="@array/text" />

倒塌的微调器:

扩大转轮:

其他回答

下面是一个覆盖Spinner视图的通用解决方案。它重写setAdapter()以将初始位置设置为-1,并代理提供的SpinnerAdapter以显示位置小于0的提示字符串。

这已经在Android 1.5到4.2上进行了测试,但买家要小心!因为这个解决方案依赖于反射来调用私有的AdapterView.setNextSelectedPositionInt()和AdapterView.setSelectedPositionInt(),所以它不能保证在未来的操作系统更新中工作。这似乎是有可能的,但这绝不是保证的。

通常我不会宽恕这样的事情,但这个问题已经被问了很多次了,这似乎是一个足够合理的要求,我认为我应该发布我的解决方案。

/**
 * A modified Spinner that doesn't automatically select the first entry in the list.
 *
 * Shows the prompt if nothing is selected.
 *
 * Limitations: does not display prompt if the entry list is empty.
 */
public class NoDefaultSpinner extends Spinner {

    public NoDefaultSpinner(Context context) {
        super(context);
    }

    public NoDefaultSpinner(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public NoDefaultSpinner(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void setAdapter(SpinnerAdapter orig ) {
        final SpinnerAdapter adapter = newProxy(orig);

        super.setAdapter(adapter);

        try {
            final Method m = AdapterView.class.getDeclaredMethod(
                               "setNextSelectedPositionInt",int.class);
            m.setAccessible(true);
            m.invoke(this,-1);

            final Method n = AdapterView.class.getDeclaredMethod(
                               "setSelectedPositionInt",int.class);
            n.setAccessible(true);
            n.invoke(this,-1);
        } 
        catch( Exception e ) {
            throw new RuntimeException(e);
        }
    }

    protected SpinnerAdapter newProxy(SpinnerAdapter obj) {
        return (SpinnerAdapter) java.lang.reflect.Proxy.newProxyInstance(
                obj.getClass().getClassLoader(),
                new Class[]{SpinnerAdapter.class},
                new SpinnerAdapterProxy(obj));
    }



    /**
     * Intercepts getView() to display the prompt if position < 0
     */
    protected class SpinnerAdapterProxy implements InvocationHandler {

        protected SpinnerAdapter obj;
        protected Method getView;


        protected SpinnerAdapterProxy(SpinnerAdapter obj) {
            this.obj = obj;
            try {
                this.getView = SpinnerAdapter.class.getMethod(
                                 "getView",int.class,View.class,ViewGroup.class);
            } 
            catch( Exception e ) {
                throw new RuntimeException(e);
            }
        }

        public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
            try {
                return m.equals(getView) && 
                       (Integer)(args[0])<0 ? 
                         getView((Integer)args[0],(View)args[1],(ViewGroup)args[2]) : 
                         m.invoke(obj, args);
            } 
            catch (InvocationTargetException e) {
                throw e.getTargetException();
            } 
            catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

        protected View getView(int position, View convertView, ViewGroup parent) 
          throws IllegalAccessException {

            if( position<0 ) {
                final TextView v = 
                  (TextView) ((LayoutInflater)getContext().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE)).inflate(
                      android.R.layout.simple_spinner_item,parent,false);
                v.setText(getPrompt());
                return v;
            }
            return obj.getView(position,convertView,parent);
        }
    }
}

对我来说,它是这样工作的。有改进,只改变文本在某些选项,而不是全部。

首先,我采用旋转器的名称并创建带有自定义视图的arrayadapter,但现在这并不重要,关键是覆盖getView,并在内部更改你需要更改的值。在我的情况下只有第一个,其余的我离开原来的

public void rellenarSpinnerCompeticiones(){
        spinnerArrayCompeticiones = new ArrayList<String>();
        for(Competicion c: ((Controlador)getApplication()).getCompeticiones()){
            spinnerArrayCompeticiones.add(c.getNombre());
        }
        //ArrayAdapter<String> spinnerArrayAdapter = new ArrayAdapter<String>(this,R.layout.spinner_item_competicion,spinnerArrayCompeticiones);
        ArrayAdapter<String> spinnerArrayAdapter = new ArrayAdapter<String>(this, R.layout.spinner_item_competicion, spinnerArrayCompeticiones){
            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                final View v = vi.inflate(R.layout.spinner_item_competicion, null);
                final TextView t = (TextView)v.findViewById(R.id.tvCompeticion);
                if(spinnerCompeticion.getSelectedItemPosition()>0){
                    t.setText(spinnerArrayCompeticiones.get(spinnerCompeticion.getSelectedItemPosition()));
                }else{
                    t.setText("Competiciones");
                }
                return v;
            }
        };
        spinnerArrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinnerCompeticion.setAdapter(spinnerArrayAdapter);
    }

此外,还有一个简单的技巧来显示默认值:

你可以在列表中添加一个默认值,然后使用list. addall (yourCollection)添加所有的集合;

下面是可操作的示例代码:

List<FuelName> fuelList = new ArrayList<FuelName>();
                    fuelList.add(new FuelName(0,"Select One"));
                    fuelList.addAll(response.body());
                    ArrayAdapter adapter = new ArrayAdapter<>(getActivity(), android.R.layout.simple_spinner_item, fuelList);
                    //fuelName.setPrompt("Select Fuel");
                    fuelName.setAdapter(adapter);

之前提交的答案都没有真正按照我想要的方式解决这个问题。对我来说,理想的解决方案是在旋转器第一次显示时提供“Select One”(或任何初始文本)。当用户点击转轮时,初始文本不应该是显示的下拉框的一部分。

为了使我的特定情况更加复杂,我的旋转器数据来自通过LoaderManager回调加载的游标。

经过大量的实验,我想出了以下解决方案:

public class MyFragment extends Fragment implements
LoaderManager.LoaderCallbacks<Cursor>{

private static final String SPINNER_INIT_VALUE = "Select A Widget";
private Spinner mSpinner;
private int mSpinnerPosition;
private boolean mSpinnerDropDownShowing = false;
private View mSpinnerDropDown;

private MyCursorAdapter mCursorAdapter;

...

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
...

mCursorAdapter = new MyCursorAdapter(getActivity());

mSpinner = (Spinner) rootView.findViewById(R.id.theSpinner);
mSpinner.setOnTouchListener(mSpinnerTouchListener);
mSpinner.setAdapter(mCursorAdapter);

...
}

//Capture the touch events to toggle the spinner's dropdown visibility
private OnTouchListener mSpinnerTouchListener = new View.OnTouchListener() {
    @Override
    public boolean onTouch(View view, MotionEvent motionEvent) {
        if(mSpinnerDropDown != null && mSpinnerDropDownShowing == false){
            mSpinnerDropDownShowing = true;
            mSpinnerDropDown.setVisibility(View.VISIBLE);
        }
        return false;
    }
};

//Capture the click event on the spinner drop down items
protected OnClickListener spinnerItemClick = new OnClickListener(){

    @Override
    public void onClick(View view) {
        String widget = ((TextView) view.findViewById(android.R.id.text1)).getText().toString();

        if(!widget.equals(SPINNER_INIT_VALUE)){
            if(mCursorAdapter != null){
                Cursor cursor = mCursorAdapter.getCursor();
                if(cursor.moveToFirst()){
                    while(!cursor.isAfterLast()){
                        if(widget.equals(cursor.getString(WidgetQuery.WIDGET_NAME))){

                            ...

                            //Set the spinner to the correct item
                            mSpinnerPosition = cursor.getPosition() + 1;
                            mSpinner.setSelection(mSpinnerPosition);
                            break;
                        }
                        cursor.moveToNext();
                    }
                }
            }
        }

        //Hide the drop down. Not the most elegent solution but it is the only way I could hide/dismiss the drop down
        mSpinnerDropDown = view.getRootView();
        mSpinnerDropDownShowing = false;
        mSpinnerDropDown.setVisibility(View.GONE);
    }
};

private class MyCursorAdapter extends CursorAdapter {

    private final int DISPLACEMENT = 1;
    private final int DEFAULT_ITEM_ID = Integer.MAX_VALUE;

    private Activity mActivity;

    public MyCursorAdapter(Activity activity) {
            super(activity, null, false);
            mActivity = activity;
    }

    //When loading the regular views, inject the defualt item
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(position == 0){
            if(convertView == null){
                convertView = mActivity.getLayoutInflater().inflate(R.layout.list_item_widget, parent, false);
            }
            return getDefaultItem(convertView);
        }
        return super.getView(position - DISPLACEMENT, convertView, parent);
    }

    //When loading the drop down views, set the onClickListener for each view
    @Override
    public View getDropDownView(int position, View convertView, ViewGroup parent){
        View view = super.getDropDownView(position, convertView, parent);
        view.setOnClickListener(spinnerItemClick);
        return view;
    }

    //The special default item that is being injected
    private View getDefaultItem(View convertView){
        TextView text = (TextView) convertView.findViewById(android.R.id.text1);
        text.setText(SPINNER_INIT_VALUE);
        return convertView;
    }

    @Override
    public long getItemId(int position) {
        if (position == 0) {
            return DEFAULT_ITEM_ID;
        }
        return super.getItemId(position - DISPLACEMENT);
    }

    @Override
    public boolean isEnabled(int position) {
        return position == 0 ? true : super.isEnabled(position - DISPLACEMENT);
    }

    @Override
    public int getViewTypeCount() {
        return super.getViewTypeCount() + DISPLACEMENT;
    }

    @Override
    public int getItemViewType(int position) {
        if (position == 0) {
            return super.getViewTypeCount();
        }

        return super.getItemViewType(position - DISPLACEMENT);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        return mActivity.getLayoutInflater().inflate(R.layout.list_item_widget, parent, false);
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor){

        if(cursor.isAfterLast()){
            return;
        }

        TextView text = (TextView) view.findViewById(android.R.id.text1);
        String WidgetName = cursor.getString(WidgetQuery.WIDGET_NAME);
        text.setText(WidgetName);
    }
}
}

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。