Skip saving/restoring state for unmounted fragments. (#313)

We currently cannot take any adventage of saving and restoring fragment state because view hierarchy of the unmounted fragment is retained by RN core anyways. Skipping sabe/restore will allow us to avoid unnecessary serializiation/deserialization of the view hierarchy but will also help circumvent some bugs which comes from the side effects of restoring. One of the bugs have been reported in #162 and in that particular case restoring result in InputText change event being triggered with stale value. This was happening in the situation when we were going back to a screen with InputText component.

android/src/main/java/com/swmansion/rnscreens/Screen.java

@@ -2,6 +2,8 @@
 
 import android.content.Context;
 import android.graphics.Paint;
+import android.os.Parcelable;
+import android.util.SparseArray;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.WindowManager;
@@ -68,6 +70,18 @@ public Screen(ReactContext context) {
     setLayoutParams(new WindowManager.LayoutParams(WindowManager.LayoutParams.TYPE_APPLICATION));
   }
 
+  @Override
+  protected void dispatchSaveInstanceState(SparseArray<Parcelable> container) {
+    // do nothing, react native will keep the view hierarchy so no need to serialize/deserialize
+    // view's states. The side effect of restoring is that TextInput components would trigger set-text
+    // events which may confuse text input handling.
+  }
+
+  @Override
+  protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {
+    // ignore restoring instance state too as we are not saving anything anyways.
+  }
+
   @Override
   protected void onLayout(boolean changed, int l, int t, int r, int b) {
     if (changed) {