6 June 2024 Leave a comment Tech-Help
Setting up a Spinner in Android that displays an initial prompt like “Select One” can be a bit tricky. This guide will walk you through the steps to achieve this using a custom adapter. The aim is to display the prompt text initially and replace it with the selected item once the user makes a choice, without showing the prompt in the dropdown list.
Solution Overview
We will create a custom adapter that wraps around the standard SpinnerAdapter. This custom adapter will handle displaying the initial prompt text and manage the selection of actual items. Here’s how you can do it:
Step-by-Step Implementation
1. Define the XML Layout for the Spinner
First, create the layout for the Spinner in your XML file:
<Spinner
android:id="@+id/mySpinner"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:spinnerMode="dropdown" />2. Create the Custom Adapter
Next, create a custom adapter class that decorates the existing SpinnerAdapter:
import android.content.Context;
import android.database.DataSetObserver;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListAdapter;
import android.widget.SpinnerAdapter;
/**
* Decorator Adapter to allow a Spinner to show a 'Nothing Selected...' initially
* displayed instead of the first choice in the Adapter.
*/
public class NothingSelectedSpinnerAdapter implements SpinnerAdapter, ListAdapter {
protected static final int EXTRA = 1;
protected SpinnerAdapter adapter;
protected Context context;
protected int nothingSelectedLayout;
protected int nothingSelectedDropdownLayout;
protected LayoutInflater layoutInflater;
public NothingSelectedSpinnerAdapter(SpinnerAdapter spinnerAdapter, int nothingSelectedLayout, Context context) {
this(spinnerAdapter, nothingSelectedLayout, -1, context);
}
public NothingSelectedSpinnerAdapter(SpinnerAdapter spinnerAdapter, int nothingSelectedLayout, int nothingSelectedDropdownLayout, Context context) {
this.adapter = spinnerAdapter;
this.context = context;
this.nothingSelectedLayout = nothingSelectedLayout;
this.nothingSelectedDropdownLayout = nothingSelectedDropdownLayout;
layoutInflater = LayoutInflater.from(context);
}
@Override
public final View getView(int position, View convertView, ViewGroup parent) {
if (position == 0) {
return getNothingSelectedView(parent);
}
return adapter.getView(position - EXTRA, null, parent);
}
protected View getNothingSelectedView(ViewGroup parent) {
return layoutInflater.inflate(nothingSelectedLayout, parent, false);
}
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
if (position == 0) {
return nothingSelectedDropdownLayout == -1 ? new View(context) : getNothingSelectedDropdownView(parent);
}
return adapter.getDropDownView(position - EXTRA, null, parent);
}
protected View getNothingSelectedDropdownView(ViewGroup parent) {
return layoutInflater.inflate(nothingSelectedDropdownLayout, parent, false);
}
@Override
public int getCount() {
int count = adapter.getCount();
return count == 0 ? 0 : count + EXTRA;
}
@Override
public Object getItem(int position) {
return position == 0 ? null : adapter.getItem(position - EXTRA);
}
@Override
public long getItemId(int position) {
return position >= EXTRA ? adapter.getItemId(position - EXTRA) : position - EXTRA;
}
@Override
public boolean hasStableIds() {
return adapter.hasStableIds();
}
@Override
public boolean isEmpty() {
return adapter.isEmpty();
}
@Override
public void registerDataSetObserver(DataSetObserver observer) {
adapter.registerDataSetObserver(observer);
}
@Override
public void unregisterDataSetObserver(DataSetObserver observer) {
adapter.unregisterDataSetObserver(observer);
}
@Override
public boolean areAllItemsEnabled() {
return false;
}
@Override
public boolean isEnabled(int position) {
return position != 0;
}
}3. Implement the Adapter in Your Activity
In your activity, you need to set up the Spinner with the custom adapter:
Spinner spinner = (Spinner) findViewById(R.id.mySpinner);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.planets_array, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(new NothingSelectedSpinnerAdapter(adapter, R.layout.contact_spinner_row_nothing_selected, this));4. Define the Layout for the Prompt
Create a layout file named contact_spinner_row_nothing_selected.xml with the following content:
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/text1"
style="?android:attr/spinnerItemStyle"
android:singleLine="true"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ellipsize="marquee"
android:textSize="18sp"
android:textColor="#808080"
android:text="[Select a Planet...]" />Additional Resources
For more advanced configurations and troubleshooting, consider visiting our documentation pages:
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