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?
最好的解决方案,我发现这实际上不是使用一个纺纱机,而是一个AutoCompleteTextView。它基本上是一个带有附加Spinner的EditText,可以在你输入时显示建议-但是,通过正确的配置,它可以完全按照OP的要求进行操作。
XML:
<com.google.android.material.textfield.TextInputLayout
android:id="@+id/item"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<androidx.appcompat.widget.AppCompatAutoCompleteTextView
android:id="@+id/input"
android:hint="Select one"
style="@style/AutoCompleteTextViewDropDown"/>
</com.google.android.material.textfield.TextInputLayout>
风格:
<style name="AutoCompleteTextViewDropDown">
<item name="android:clickable">false</item>
<item name="android:cursorVisible">false</item>
<item name="android:focusable">false</item>
<item name="android:focusableInTouchMode">false</item>
<item name="android:layout_width">match_parent</item>
<item name="android:layout_height">wrap_content</item>
</style>
至于适配器,使用基本的ArrayAdapter或扩展它来创建自己的适配器,但不需要在适配器方面进行额外的定制。在AutoCompleteTextView上设置适配器。
我得到了同样的问题旋转,与一个空的选择,我找到了一个更好的解决方案。看看这段简单的代码。
Spinner lCreditOrDebit = (Spinner)lCardPayView.findViewById(R.id.CARD_TYPE);
spinneradapter lAdapter =
new spinneradapter(
BillPayScreen.this,
ndroid.R.layout.simple_spinner_item,getResources().getStringArray(R.array.creditordebit));
lAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
lCreditOrDebit.setAdapter(lAdapter);
这里spinneradapter是对arrayadapter的一个小定制。它是这样的:
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
public class spinneradapter extends ArrayAdapter<String>{
private Context m_cContext;
public spinneradapter(Context context,int textViewResourceId, String[] objects) {
super(context, textViewResourceId, objects);
this.m_cContext = context;
}
boolean firsttime = true;
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(firsttime){
firsttime = false;
//Just return some empty view
return new ImageView(m_cContext);
}
//Let the array adapter take care of it this time.
return super.getView(position, convertView, parent);
}
}
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;
}
}
//...
}
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。
没有默认的API来设置微调提示。为了添加它,我们需要一个小的解决方案,而不是安全反射实现
List<Object> objects = new ArrayList<Object>();
objects.add(firstItem);
objects.add(secondItem);
// add hint as last item
objects.add(hint);
HintAdapter adapter = new HintAdapter(context, objects, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
Spinner spinnerFilmType = (Spinner) findViewById(R.id.spinner);
spinner.setAdapter(adapter);
// show hint
spinner.setSelection(adapter.getCount());
适配器来源:
public class HintAdapter
extends ArrayAdapter<Objects> {
public HintAdapter(Context theContext, List<Object> objects) {
super(theContext, android.R.id.text1, android.R.id.text1, objects);
}
public HintAdapter(Context theContext, List<Object> objects, int theLayoutResId) {
super(theContext, theLayoutResId, android.R.id.text1, objects);
}
@Override
public int getCount() {
// don't display last item. It is used as hint.
int count = super.getCount();
return count > 0 ? count - 1 : count;
}
}
原始来源