Add "frame" : scrollable area.

examples/component/checkbox_in_frame.cpp

@@ -0,0 +1,42 @@
+#include "ftxui/component/checkbox.hpp"
+#include "ftxui/component/container.hpp"
+#include "ftxui/component/input.hpp"
+#include "ftxui/component/menu.hpp"
+#include "ftxui/component/checkbox.hpp"
+#include "ftxui/component/screen_interactive.hpp"
+#include "ftxui/component/toggle.hpp"
+#include "ftxui/screen/string.hpp"
+
+using namespace ftxui;
+
+class MyComponent : public Component {
+ public:
+  MyComponent() {
+    Add(&container);
+    checkbox.resize(30);
+    for(int i = 0; i<checkbox.size(); ++i) {
+      checkbox[i].label = (L"CheckBox " + to_wstring(i));
+      container.Add(&checkbox[i]);
+    }
+  }
+
+  Element Render() override {
+    Elements content;
+    for(auto& it : checkbox) {
+      content.push_back(it.Render());
+    }
+    return vbox(std::move(content)) | frame | size(20, 10) | border;
+  }
+
+ private:
+  std::vector<CheckBox> checkbox;
+  Container container = Container::Vertical();
+};
+
+int main(int argc, const char* argv[]) {
+  auto screen = ScreenInteractive::FitComponent();
+  MyComponent component;
+  screen.Loop(&component);
+
+  return 0;
+}