implement android.widget.Spinner using GtkDropDown

Helper classes from ListView implementation are reused. The declarations
have been moved to a new header file AdaperView.h

src/api-impl/android/widget/AbsSpinner.java

@@ -1,16 +1,52 @@
 package android.widget;
 
 import android.content.Context;
+import android.database.DataSetObserver;
 import android.util.AttributeSet;
 
 public abstract class AbsSpinner extends AdapterView {
+	private Observer observer = new Observer();
 
 	public AbsSpinner(Context context) {
 		super(context);
+		haveCustomMeasure = false;
 	}
 
 	public AbsSpinner(Context context, AttributeSet attributeSet) {
 		super(context, attributeSet);
+		haveCustomMeasure = false;
 	}
 
+	@Override
+	protected native long native_constructor(Context context, AttributeSet attrs);
+	protected native void native_setAdapter(long widget, SpinnerAdapter adapter);
+
+	public void setAdapter(SpinnerAdapter adapter) {
+		SpinnerAdapter oldAdapter = getAdapter();
+		if (oldAdapter != null)
+			oldAdapter.unregisterDataSetObserver(observer);
+		super.setAdapter(adapter);
+		if (adapter != null)
+			adapter.registerDataSetObserver(observer);
+		native_setAdapter(this.widget, adapter);
+	}
+
+	public SpinnerAdapter getAdapter() {
+		return (SpinnerAdapter) super.getAdapter();
+	}
+
+	@Override
+	public native void setOnItemSelectedListener(AdapterView.OnItemSelectedListener listener);
+
+	private class Observer extends DataSetObserver {
+
+		@Override
+		public void onChanged() {
+			AbsSpinner.this.native_setAdapter(widget, getAdapter());
+		}
+		@Override
+		public void onInvalidated() {
+			AbsSpinner.this.native_setAdapter(widget, getAdapter());
+		}
+	}
 }

src/api-impl/android/widget/Spinner.java

@@ -13,8 +13,4 @@ public class Spinner extends AbsSpinner {
 		super(context, attributeSet);
 	}
 
-	public void setAdapter(SpinnerAdapter adapter) {
-		super.setAdapter(adapter);
-	}
-
 }