Add ability to invalidate views

Summary: When some drawing attributes of a view changes how it measures, we need to be able to relayout it correctly.  This adds method `invalidate(View)` to `YogaLayout` which will flag the corresponding node as dirty and requiring layout again.

Reviewed By: emilsjolander

Differential Revision: D4634563

fbshipit-source-id: af7f47dce00a31414d0987a58307c5d44c1bcf20

android/src/main/java/com/facebook/yoga/android/YogaLayout.java

@@ -231,6 +231,28 @@ public class YogaLayout extends ViewGroup {
     super.removeAllViewsInLayout();
   }
 
+  /**
+   * Marks a particular view as "dirty" and to be relaid out.  If the view is not a child of this
+   * {@link YogaLayout}, the entire tree is traversed to find it.
+   *
+   * @param view the view to mark as dirty
+   */
+  public void invalidate(View view) {
+    if (mYogaNodes.containsKey(view)) {
+      mYogaNodes.get(view).dirty();
+      return;
+    }
+
+    final int childCount = mYogaNode.getChildCount();
+    for (int i = 0; i < childCount; i++) {
+      final YogaNode yogaNode = mYogaNode.getChildAt(i);
+      if (yogaNode.getData() instanceof YogaLayout) {
+        ((YogaLayout) yogaNode.getData()).invalidate(view);
+      }
+    }
+    invalidate();
+  }
+
   private void removeViewFromYogaTree(View view, boolean inLayout) {
     final YogaNode node = mYogaNodes.get(view);
     if (node == null) {
@@ -293,9 +315,7 @@ public class YogaLayout extends ViewGroup {
   protected void onLayout(boolean changed, int l, int t, int r, int b) {
     // Either we are a root of a tree, or this function is called by our parent's onLayout, in which
     // case our r-l and b-t are the size of our node.
-    if (!(getParent() instanceof YogaLayout) &&
-        Math.round(mYogaNode.getLayoutHeight()) != b-t &&
-        Math.round(mYogaNode.getLayoutWidth()) != r-l) {
+    if (!(getParent() instanceof YogaLayout)) {
         createLayout(
             MeasureSpec.makeMeasureSpec(r - l, MeasureSpec.EXACTLY),
             MeasureSpec.makeMeasureSpec(b - t, MeasureSpec.EXACTLY));

docs/_docs/api/android.md

@@ -30,3 +30,9 @@ The list of all attributes can be found in [attrs.xml](https://github.com/facebo
 ## Auto margins
 
 You can specify `margin_left="auto"` (or `margin_right` etc.) for auto values.  This is in addition to the dimensions you can speicfy, such as `margin_left="20dp"`.
+
+## Invalidation (_temporary_)
+
+If you change any attribute of a view that will change its measure size, you must invalidate it.  Do this by calling `YogaLayout#invalidate(View)` on any `YogaLayout` further up the tree.  Obviously it is most efficient to call it on the view's parent (if it is a `YogaLayout`, but in case this is impractical, you can call it on the root of the tree.
+
+This is a temporary solution.  Ideally, the view should invalidate itself whenever an attribute (text, font etc.) that will alter its size changes.  This will be automatic once we find a good way to hook into the Android invalidation system.