I have a layout, default_label.xml
, like so:
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/label"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
Then, I have this class, which basically allows me to set the default button text for a spinner:
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;
protected TextView label;
/**
* Use this constructor to have NO 'Select One...' item, instead use
* the standard prompt or nothing at all.
*
* @param spinnerAdapter wrapped Adapter.
* @param nothingSelectedLayout layout for nothing selected, perhaps
* you want text grayed out like a prompt...
* @param context Context
*/
public NothingSelectedSpinnerAdapter(
SpinnerAdapter spinnerAdapter,
int nothingSelectedLayout, Context context) {
this(spinnerAdapter, nothingSelectedLayout, -1, context);
}
/**
* Use this constructor to Define your 'Select One...' layout as the first
* row in the returned choices.
* If you do this, you probably don't want a prompt on your spinner or it'll
* have two 'Select' rows.
*
* @param spinnerAdapter wrapped Adapter. Should probably return false for isEnabled(0)
* @param nothingSelectedLayout layout for nothing selected, perhaps you want
* text grayed out like a prompt...
* @param nothingSelectedDropdownLayout layout for your 'Select an Item...' in
* the dropdown.
* @param context 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) {
// 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);
}
return adapter.getView(position - EXTRA, null, parent); // Could re-use
// the convertView if possible.
}
public int getPosition(String value) {
int index = 0;
for (int i = 1; i < getCount() + EXTRA; i++) {
if (getItem(i).equals(value)) {
index = i;
break;
}
}
return index;
}
public TextView getNothingSelectedView(ViewGroup parent) {
label = (TextView) layoutInflater.inflate(nothingSelectedLayout, parent, false);
return label;
}
@Override
public 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 new View(context);
}
if (adapter.getItem(position-EXTRA).toString().equals("")){
View view = nothingSelectedDropdownLayout == -1 ?
new View(context) :
getNothingSelectedDropdownView(parent);
view.setEnabled(false);
view.setOnClickListener(null);
return view;
}
// Could re-use the convertView if possible, use setTag...
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 int getItemViewType(int position) {
return 0;
}
@Override
public int getViewTypeCount() {
return 1;
}
@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; // Don't allow the 'nothing selected'
// item to be picked.
}
}
What I want to be able to do is change the text of the TextView
, something like:
NothingSelectedSpinnerAdapter myAdapter = new NothingSelectedSpinnerAdapter(adapter, R.layout.default_label, getContext());
myAdapter.setText("Custom Label");
mySpinner.setAdapter(myAdapter);
However, when I try adding the following method to the above NothingSelectedSpinnerAdapter
class:
public void setText(String text) {
label.setText(text);
}
I get the following error:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
What should I change?
Take a look at the following three lines:
NothingSelectedSpinnerAdapter myAdapter = new NothingSelectedSpinnerAdapter(adapter, R.layout.default_label, getContext());
The Adapter is instantiated, label is null
myAdapter.setText("Custom Label");
The TextView
label is still null
, that's why label.setText();
causes a NullPointerException
mySpinner.setAdapter(myAdapter);
Now the runtime will be able to draw the Spinner
items. This involves repeated calling of getView()
(at least once for every item which should be drawn). After getView()
has been executed for position = 0
, you will have assigned a value to label . From now on, you can safely call setText()
on it.
If you want to be able to call myAdapter.setText("Custom Label");
whenever you like without having to bother about the inner workings of the Adapter, then you can introduce a field private String mLabelText
and implement the method as follows
public void setText(String labelText){
mLabelText = labelText;
if (label != null){
label.setText(labelText);
}
}
One last step: don't forget to set the text right after initializing label
public TextView getNothingSelectedView(ViewGroup parent) {
label = (TextView) layoutInflater.inflate(nothingSelectedLayout, parent, false);
label.setText(mLabelText);
return label;
}
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