我找不到使用微调器获得这种行为的方法，所以唯一对我有用的是使用微调器（自定义）适配器：
public interface SpinnerListener {
void onSpinnerExpanded();
void onSpinnerCollapsed();
}
然后可以编写一个自定义适配器，它只抓取“旋转器展开”视图并向其添加一个侦听器以侦听“展开”和“折叠”事件。我使用的自定义适配器是：
public class ListeningArrayAdapter<T> extends ArrayAdapter<T> {
private ViewGroup itemParent;
private final Collection<SpinnerListener> spinnerListeners = new ArrayList<SpinnerListener>();
public ListeningArrayAdapter(Context context, int resource, T[] objects) {
super(context, resource, objects);
}
// Add the rest of the constructors here ...
// Just grab the spinner view (parent of the spinner item view) and add a listener to it.
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
if (isParentTheListView(parent)) {
itemParent = parent;
addFocusListenerAsExpansionListener();
}
return super.getDropDownView(position, convertView, parent);
}
// Assumes the item view parent is a ListView (which it is when a Spinner class is used)
private boolean isParentTheListView(ViewGroup parent) {
return (parent != itemParent && parent != null && ListView.class.isAssignableFrom(parent.getClass()));
}
// Add a focus listener to listen to spinner expansion and collapse events.
private void addFocusListenerAsExpansionListener() {
final View.OnFocusChangeListener listenerWrapper = new OnFocusChangeListenerWrapper(itemParent.getOnFocusChangeListener(), spinnerListeners);
itemParent.setOnFocusChangeListener(listenerWrapper);
}
// Utility method.
public boolean isExpanded() {
return (itemParent != null && itemParent.hasFocus());
}
public void addSpinnerListener(SpinnerListener spinnerListener) {
spinnerListeners.add(spinnerListener);
}
public boolean removeSpinnerListener(SpinnerListener spinnerListener) {
return spinnerListeners.remove(spinnerListener);
}
// Listener that listens for 'expand' and 'collapse' events.
private static class OnFocusChangeListenerWrapper implements View.OnFocusChangeListener {
private final Collection<SpinnerListener> spinnerListeners;
private final View.OnFocusChangeListener originalFocusListener;
private OnFocusChangeListenerWrapper(View.OnFocusChangeListener originalFocusListener, Collection<SpinnerListener> spinnerListeners) {
this.spinnerListeners = spinnerListeners;
this.originalFocusListener = originalFocusListener;
}
@Override
public void onFocusChange(View view, boolean hasFocus) {
if (originalFocusListener != null) {
originalFocusListener.onFocusChange(view, hasFocus); // Preserve the pre-existing focus listener (if any).
}
callSpinnerListeners(hasFocus);
}
private void callSpinnerListeners(boolean hasFocus) {
for (SpinnerListener spinnerListener : spinnerListeners) {
if (spinnerListener != null) {
callSpinnerListener(hasFocus, spinnerListener);
}
}
}
private void callSpinnerListener(boolean hasFocus, SpinnerListener spinnerListener) {
if (hasFocus) {
spinnerListener.onSpinnerExpanded();
}
else {
spinnerListener.onSpinnerCollapsed();
}
}
}
}
然后，当我在我的活动或片段中使用微调器时，我所要做的就是将微调器适配器设置为上述自定义适配器：
private ListeningArrayAdapter<CharSequence> adapter;
private Spinner buildSpinner() {
final CharSequence[] items = {"One", "Two", "Three"};
final Spinner spinner = (Spinner)getActivity().getLayoutInflater().inflate(R.layout.item_spinner, null);
adapter = new ListeningArrayAdapter<CharSequence>(getActivity(), R.layout.item_spinner_item, items);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
adapter.addSpinnerListener(new TestSpinnerListener(getActivity())); // Add your own spinner listener implementation here.
spinner.setAdapter(adapter);
return spinner;
}
我知道这有点小技巧，有点脆弱，但它对我有用。如果 Spinner 类内置了所有这些功能并允许您设置展开-折叠侦听器，那就更好了。暂时我将不得不处理这个黑客。