Merge pull request #2984 from Hixie/table

More table fixes

packages/flutter/lib/src/rendering/table.dart

@@ -491,7 +491,7 @@ class RenderTable extends RenderBox {
         assert(_rows == 0);
         return;
       }
-      for (RenderBox oldChild in cells) {
+      for (RenderBox oldChild in _children) {
         if (oldChild != null)
           dropChild(oldChild);
       }
@@ -503,8 +503,8 @@ class RenderTable extends RenderBox {
     assert(cells != null);
     assert(cells.length % columns == 0);
     // remove cells that are moving away
-    for (int y = 0; y < _columns; y += 1) {
-      for (int x = 0; x < _rows; x += 1) {
+    for (int y = 0; y < _rows; y += 1) {
+      for (int x = 0; x < _columns; x += 1) {
         int xyOld = x + y * _columns;
         int xyNew = x + y * columns;
         if (_children[xyOld] != null && (x >= columns || xyNew >= cells.length || _children[xyOld] != cells[xyNew]))
@@ -567,6 +567,8 @@ class RenderTable extends RenderBox {
     assert(_children.length == rows * columns);
     final int xy = x + y * columns;
     RenderBox oldChild = _children[xy];
+    if (oldChild == value)
+      return;
     if (oldChild != null)
       dropChild(oldChild);
     _children[xy] = value;
@@ -759,6 +761,7 @@ class RenderTable extends RenderBox {
         RenderBox child = _children[xy];
         if (child != null) {
           TableCellParentData childParentData = child.parentData;
+          assert(childParentData != null);
           childParentData.x = x;
           childParentData.y = y;
           switch (childParentData.verticalAlignment ?? defaultVerticalAlignment) {

packages/flutter/test/rendering/table_test.dart

@@ -71,4 +71,24 @@ void main() {
     table.rows = 4;
     expect(child.attached, isFalse);
   });
+
+  test('Table test: replacing cells', () {
+    RenderTable table;
+    RenderBox child1 = new RenderPositionedBox();
+    RenderBox child2 = new RenderPositionedBox();
+    RenderBox child3 = new RenderPositionedBox();
+    table = new RenderTable();
+    table.setFlatChildren(3, <RenderBox>[child1, new RenderPositionedBox(), child2,
+                                         new RenderPositionedBox(), child3, new RenderPositionedBox()]);
+    expect(table.rows, equals(2));
+    layout(table);
+    table.setFlatChildren(3, <RenderBox>[new RenderPositionedBox(), child1, new RenderPositionedBox(),
+                                         child2, new RenderPositionedBox(), child3]);
+    layout(table);
+    table.setFlatChildren(3, <RenderBox>[new RenderPositionedBox(), child1, new RenderPositionedBox(),
+                                         child2, new RenderPositionedBox(), child3]);
+    layout(table);
+    expect(table.columns, equals(3));
+    expect(table.rows, equals(2));
+  });
 }