refactor(android): extract FragmentBase class (#154)

android/widgets/src/main/java/org/nativescript/widgets/AnimatorHelper.java

@@ -0,0 +1,61 @@
+package org.nativescript.widgets;
+
+import android.animation.Animator;
+import android.animation.AnimatorSet;
+import android.animation.ObjectAnimator;
+
+class AnimatorHelper {
+    static final int version = android.os.Build.VERSION.SDK_INT;
+    static final int exitFakeResourceId = -20;
+
+    static Animator createDummyAnimator(long duration) {
+        float[] alphaValues = new float[2];
+        alphaValues[0] = 1;
+        alphaValues[1] = 1;
+
+        Animator animator = ObjectAnimator.ofFloat(null, "alpha", alphaValues);
+        if (duration > 0) {
+            animator.setDuration(duration);
+        }
+
+        return animator;
+    }
+
+    static long getTotalDuration(Animator animator) {
+        if (animator instanceof AnimatorSet) {
+            return getAnimatorSetTotalDuration((AnimatorSet)animator);
+        } else {
+            return getAnimatorTotalDuration(animator);
+        }
+    }
+
+    static long getAnimatorTotalDuration(Animator animator) {
+        long totalDuration;
+        if (version >= 24) {
+            totalDuration = animator.getTotalDuration();
+        } else {
+            long duration = animator.getDuration();
+            if (duration == Animator.DURATION_INFINITE) {
+                totalDuration = Animator.DURATION_INFINITE;
+            } else {
+                totalDuration = animator.getStartDelay() + duration;
+            }
+        }
+
+        return totalDuration;
+    }
+
+    static long getAnimatorSetTotalDuration(AnimatorSet animatorSet) {
+        long totalDuration = 0;
+        if (version >= 24) {
+            totalDuration = animatorSet.getTotalDuration();
+        } else {
+            // TODO: this is only meaningful for "playTogether" animators
+            for (Animator animator: animatorSet.getChildAnimations()) {
+                totalDuration = Math.max(totalDuration, getTotalDuration(animator));
+            }
+        }
+
+        return totalDuration;
+    }
+}

android/widgets/src/main/java/org/nativescript/widgets/FragmentBase.java

@@ -0,0 +1,36 @@
+package org.nativescript.widgets;
+
+import android.animation.Animator;
+import android.support.v4.app.Fragment;
+
+public abstract class FragmentBase extends Fragment {
+
+    @Override
+    public Animator onCreateAnimator(int transit, boolean enter, int nextAnim) {
+        // [nested frames / fragments] apply dummy animator to the nested fragment with
+        // the same duration as the exit animator of the removing parent fragment to work around
+        // https://code.google.com/p/android/issues/detail?id=55228 (child fragments disappear
+        // when parent fragment is removed as all children are first removed from parent)
+        if (!enter) {
+            Fragment removingParentFragment = this.getRemovingParentFragment();
+            if (removingParentFragment != null) {
+                Animator parentAnimator = removingParentFragment.onCreateAnimator(transit, enter, AnimatorHelper.exitFakeResourceId);
+                if (parentAnimator != null) {
+                    long duration = AnimatorHelper.getTotalDuration(parentAnimator);
+                    return AnimatorHelper.createDummyAnimator(duration);
+                }
+            }
+        }
+
+        return super.onCreateAnimator(transit, enter, nextAnim);
+    }
+
+    public Fragment getRemovingParentFragment() {
+        Fragment parentFragment = this.getParentFragment();
+        while (parentFragment != null && !parentFragment.isRemoving()) {
+            parentFragment = parentFragment.getParentFragment();
+        }
+
+        return parentFragment;
+    }
+}