Fix onItemSelected firing for ReactPicker on initial layout.

Reviewed By: AaaChiuuu

Differential Revision: D3732557

fbshipit-source-id: ed031dbf205996dab8cb0555af972e6f26c0d202

Author: donyu

ReactAndroid/src/main/java/com/facebook/react/views/picker/ReactPicker.java

@@ -79,6 +79,10 @@ public void requestLayout() {
 
   public void setOnSelectListener(@Nullable OnSelectListener onSelectListener) {
     if (getOnItemSelectedListener() == null) {
+      // onItemSelected gets fired immediately after layout because checkSelectionChanged() in
+      // AdapterView updates the selection position from the default INVALID_POSITION. To match iOS
+      // behavior, we don't want the event emitter for onItemSelected to fire right after layout.
+      mSuppressNextEvent = true;
       setOnItemSelectedListener(
           new OnItemSelectedListener() {
             @Override