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?
考虑有N个项目要选择。
添加完这N个项目后,添加提示文本作为(N+1)个项目。
将所选项目设置为第N个位置[(N+1)个项目]。
在OnItemSelected Listener中,如果所选位置不是N,弹出最后一个项目并调用Adapter.notifyDataSetChanged()并将所选项目设置为所选位置。
就像这样:
spinner.setItems("Daily", "One time", "Frequency"); // here "Frequency is the hint text"
spinner.setSelectedIndex(2);
spinner.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(Spinner view, int position, long id, Object item) {
if (position != 2) {
view.setItems("Daily", "One time");
view.setSelectedIndex(position);
}else {
// This item is not a valid selection
}
}
});
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;
}
}
}
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。
When extending SpinnerAdapter, you override two View-producing methods, getView(int, View, ViewGroup) and getDropDownView(int, View, ViewGroup). The first one supplies the View inserted into the Spinner itself; the second supplies the View in the drop-down list (as the name suggests). You can override the getView(...) so that, until an item has been selected, it displays a TextView containing a prompt; then, when you detect an item has been selected, you change it to display a TextView corresponding to that.
public class PromptingAdapter extends SpinnerAdapter {
//... various code ...
private boolean selectionmade = false;
//call this method from the OnItemSelectedListener for your Spinner
public setSelectionState(boolean b) {
selectionmade = b;
}
@Override
public View getView(int position, View recycle, ViewGroup container) {
if(selectionmade) {
//your existing code to supply a View for the Spinner
//you could even put "return getDropDownView(position, recycle, container);"
}
else {
View output;
if(recycle instanceof TextView) {
output = recycle;
}
else {
output = new TextView();
//and layout stuff
}
output.setText(R.string.please_select_one);
//put a string "please_select_one" in res/values/strings.xml
return output;
}
}
//...
}
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);
}
}
我通过使用按钮而不是旋转器来处理这个问题。我在GitHub上有样本项目。
在项目中,我同时显示旋转器和按钮,以显示它们确实看起来相同。除了按钮,你可以将初始文本设置为任何你想要的。
下面是活动的样子:
package com.stevebergamini.spinnerbutton;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Spinner;
public class MainActivity extends Activity {
Spinner spinner1;
Button button1;
AlertDialog ad;
String[] countries;
int selected = -1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
spinner1 = (Spinner) findViewById(R.id.spinner1);
button1 = (Button) findViewById(R.id.button1);
countries = getResources().getStringArray(R.array.country_names);
// You can also use an adapter for the allert dialog if you'd like
// ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, countries);
ad = new AlertDialog.Builder(MainActivity.this).setSingleChoiceItems(countries, selected,
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
button1.setText(countries[which]);
selected = which;
ad.dismiss();
}}).setTitle(R.string.select_country).create();
button1.setOnClickListener( new OnClickListener(){
@Override
public void onClick(View v) {
ad.getListView().setSelection(selected);
ad.show();
}});
}
}
注意:是的,我意识到这是依赖于应用的主题和外观将略有不同,如果使用Theme. holo。但是,如果您使用的是遗留主题之一,如Theme。黑色,你可以开始了。