Added views::ViewModelT<T>, a type-safe template version of ViewModel.

ui/views/view_model.h

Index: ui/views/view_model.h
diff --git a/ui/views/view_model.h b/ui/views/view_model.h
index e8c84a9568edfdb311eeca8bafea671700b96eaa..fd4a78deec700749c614fe135265c77bd579c04d 100644
--- a/ui/views/view_model.h
+++ b/ui/views/view_model.h
@@ -16,19 +16,14 @@ namespace views {
 
 class View;
 
-// ViewModel is used to track an 'interesting' set of a views. Often times
-// during animations views are removed after a delay, which makes for tricky
-// coordinate conversion as you have to account for the possibility of the
-// indices from the model not lining up with those you expect. This class lets
-// you define the 'interesting' views and operate on those views.
-class VIEWS_EXPORT ViewModel {
+// Internal implementation of the templated ViewModel class. Provides
+// non-templated "unsafe" methods for ViewModel to wrap around. Any methods that
+// allow insertion of or access to a View* should be protected, and have a
+// public method in the ViewModel subclass that provides type-safe access to the
+// correct View subclass.
+class VIEWS_EXPORT ViewModelBase {
  public:
-  ViewModel();
-  ~ViewModel();
-
-  // Adds |view| to this model. This does not add |view| to a view hierarchy,
-  // only to this model.
-  void Add(View* view, int index);
+  ~ViewModelBase();
 
   // Removes the view at the specified index. This does not actually remove the
   // view from the view hierarchy.
@@ -50,8 +45,10 @@ class VIEWS_EXPORT ViewModel {
   // Removes and deletes all the views.
   void Clear();
 
-  // Returns the view at the specified index.
-  View* view_at(int index) const {
+  // Returns the view at the specified index. Note: Most users should use
+  // view_at() in the subclass, to get a view of the correct type. (Do not call
+  // ViewAtBase then static_cast to the desired type.)
+  View* ViewAtBase(int index) const {

[sky, 2014/10/01 19:20:37]

Can we name this view_at and the subclass implementation t_at or view_t_at?
Alternatively make this protected and friend ViewModelUtils and leave the names
you have.

[Matt Giuca, 2014/10/02 01:23:51]

I think I prefer the friends approach (since "normal code" should not be
accessing ViewAtBase, only this special class).

     check_index(index);
     return entries_[index].view;
   }
@@ -70,6 +67,13 @@ class VIEWS_EXPORT ViewModel {
   // model.
   int GetIndexOfView(const View* view) const;
 
+ protected:
+  ViewModelBase();
+
+  // Adds |view| to this model. This does not add |view| to a view hierarchy,
+  // only to this model.
+  void AddUnsafe(View* view, int index);
+
  private:
   struct Entry {
     Entry() : view(NULL) {}
@@ -90,7 +94,28 @@ class VIEWS_EXPORT ViewModel {
 
   Entries entries_;
 
-  DISALLOW_COPY_AND_ASSIGN(ViewModel);
+  DISALLOW_COPY_AND_ASSIGN(ViewModelBase);
+};
+
+// ViewModel is used to track an 'interesting' set of a views. Often times
+// during animations views are removed after a delay, which makes for tricky
+// coordinate conversion as you have to account for the possibility of the
+// indices from the model not lining up with those you expect. This class lets
+// you define the 'interesting' views and operate on those views.
+template <class T>
+class ViewModel : public ViewModelBase {

[sky, 2014/10/01 19:20:38]

I like naming this ViewModelT and having classes that use this typedef to
ViewModel.

[Matt Giuca, 2014/10/02 01:23:51]

Done.

+ public:
+  ViewModel<T>() {}
+
+  // Adds |view| to this model. This does not add |view| to a view hierarchy,
+  // only to this model.
+  void Add(T* view, int index) { AddUnsafe(view, index); }
+
+  // Returns the view at the specified index.
+  T* view_at(int index) const { return static_cast<T*>(ViewAtBase(index)); }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ViewModel<T>);
 };
 
 }  // namespace views