Change the way how some widgets are measured, minimumVisibleContentSize() for widgets which content can be bigger than widget size.

src/dlangui/widgets/grid.d

@@ -1533,6 +1533,29 @@ class GridWidgetBase : ScrollWidgetBase, GridModelAdapter, MenuItemActionHandler
             sz.y += _rowHeights[i];
         return sz;
     }
+    
+    /// calculate minimum size of widget
+    override Point minimumVisibleContentSize() {
+        Point sz;
+        if (_cols == 0 || _rows == 0) {
+             sz.x = 100;
+             sz.y = 100;
+             return sz;
+        }
+        // width:
+        if (_cols < 2)
+            sz.x = _colWidths[0];
+        else
+            sz.x = _colWidths[0] + _colWidths[1];
+        
+        // height
+        if (_rows < 2)
+            sz.y = _rowHeights[0];
+        else
+            sz.y = _rowHeights[0] + _rowHeights[1];
+                
+        return sz;
+    }
 
     override protected void drawClient(DrawBuf buf) {
         if (!_cols || !_rows)

src/dlangui/widgets/lists.d

@@ -942,6 +942,11 @@ class ListWidget : WidgetGroup, OnScrollHandler, OnAdapterChangeHandler {
         if (_adapter)
             _adapter.onThemeChanged();
     }
+    
+    /// sets minimum size for the list, override to change
+    Point minimumVisibleContentSize() {
+        return Point(100, 100);
+    }
 
     /// Measure widget according to desired width and height constraints. (Step 1 of two phase layout).
     override void measure(int parentWidth, int parentHeight) {
@@ -953,6 +958,15 @@ class ListWidget : WidgetGroup, OnScrollHandler, OnAdapterChangeHandler {
             _itemSizes.length = itemCount;
         Rect m = margins;
         Rect p = padding;
+        
+        // set widget area to small when first measure
+        if (parentWidth == SIZE_UNSPECIFIED && parentHeight == SIZE_UNSPECIFIED)
+        {
+            Point sz = minimumVisibleContentSize;
+            measuredContent(parentWidth, parentHeight, sz.x, sz.y);
+            return;
+        }
+        
         // calc size constraints for children
         int pwidth = parentWidth;
         int pheight = parentHeight;
@@ -1041,6 +1055,7 @@ class ListWidget : WidgetGroup, OnScrollHandler, OnAdapterChangeHandler {
             }
         }
         measuredContent(parentWidth, parentHeight, sz.x + _sbsz.x, sz.y + _sbsz.y);
+
         if (_scrollbar.visibility == oldScrollbarVisibility) {
             _needLayout = oldNeedLayout;
             _scrollbar.cancelLayout();

src/dlangui/widgets/scroll.d

@@ -273,6 +273,11 @@ class ScrollWidgetBase :  WidgetGroup, OnScrollHandler {
         return sz;
     }
 
+    // override to set minimum scrollwidget size - default 100x100
+    Point minimumVisibleContentSize() {
+        return Point(100,100);
+    }
+
     /// Measure widget according to desired width and height constraints. (Step 1 of two phase layout).
     override void measure(int parentWidth, int parentHeight) { 
         if (visibility == Visibility.Gone) {
@@ -280,6 +285,7 @@ class ScrollWidgetBase :  WidgetGroup, OnScrollHandler {
         }
         Rect m = margins;
         Rect p = padding;
+        
         // calc size constraints for children
         int pwidth = parentWidth;
         int pheight = parentHeight;
@@ -293,13 +299,14 @@ class ScrollWidgetBase :  WidgetGroup, OnScrollHandler {
         if (_vscrollbar && _vscrollbarMode == ScrollBarMode.Visible) {
             _vscrollbar.measure(pwidth, pheight);
         }
-        Point sz = fullContentSize();
+        Point sz = minimumVisibleContentSize();
         if (_hscrollbar && _hscrollbarMode == ScrollBarMode.Visible) {
             sz.y += _hscrollbar.measuredHeight;
         }
         if (_vscrollbar && _vscrollbarMode == ScrollBarMode.Visible) {
             sz.x += _vscrollbar.measuredWidth;
         }
+
         measuredContent(parentWidth, parentHeight, sz.x, sz.y);
     }
 

src/dlangui/widgets/tree.d

@@ -813,6 +813,10 @@ class TreeWidgetBase :  ScrollWidget, OnTreeContentChangeListener, OnTreeStateCh
         super.layout(rc);
     }
 
+    override Point minimumVisibleContentSize() {
+        return Point(200,200);
+    }
+
     /// Measure widget according to desired width and height constraints. (Step 1 of two phase layout).
     override void measure(int parentWidth, int parentHeight) { 
         if (visibility == Visibility.Gone) {