Added WindowDragArea.maximizable property (#1077)

* Fix window transparency

Related issue: leanflutter/window_manager#293

* Custom `WindowDragArea` with `maximizable` prop

Close #1056

Author: FeodorFitsner

client/macos/Runner/MainFlutterWindow.swift

@@ -4,6 +4,7 @@ import FlutterMacOS
 class MainFlutterWindow: NSWindow {
   override func awakeFromNib() {
     let flutterViewController = FlutterViewController.init()
+    flutterViewController.backgroundColor = .clear
     let windowFrame = self.frame
     self.contentViewController = flutterViewController
     self.setFrame(windowFrame, display: true)

package/lib/src/controls/window_drag_area.dart

@@ -25,6 +25,7 @@ class WindowDragAreaControl extends StatelessWidget {
 
     var contentCtrls =
         children.where((c) => c.name == "content" && c.isVisible);
+    bool maximizable = control.attrBool("maximizable", true)!;
     bool disabled = control.isDisabled || parentDisabled;
 
     if (contentCtrls.isEmpty) {
@@ -33,9 +34,40 @@ class WindowDragAreaControl extends StatelessWidget {
 
     return constrainedControl(
         context,
-        DragToMoveArea(
+        WindowDragArea(
+            maximizable: maximizable,
             child: createControl(control, contentCtrls.first.id, disabled)),
         parent,
         control);
   }
 }
+
+class WindowDragArea extends StatelessWidget {
+  final Widget child;
+  final bool maximizable;
+
+  const WindowDragArea(
+      {Key? key, required this.child, required this.maximizable})
+      : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      behavior: HitTestBehavior.translucent,
+      onPanStart: (details) {
+        windowManager.startDragging();
+      },
+      onDoubleTap: maximizable
+          ? () async {
+              bool isMaximized = await windowManager.isMaximized();
+              if (!isMaximized) {
+                windowManager.maximize();
+              } else {
+                windowManager.unmaximize();
+              }
+            }
+          : null,
+      child: child,
+    );
+  }
+}

sdk/python/packages/flet-core/src/flet_core/window_drag_area.py

@@ -71,6 +71,7 @@ def __init__(
         visible: Optional[bool] = None,
         disabled: Optional[bool] = None,
         data: Any = None,
+        maximizable: Optional[bool] = None,
     ):
 
         ConstrainedControl.__init__(
@@ -105,6 +106,7 @@ def __init__(
         self.__content: Optional[Control] = None
 
         self.content = content
+        self.maximizable = maximizable
 
     def _get_control_name(self):
         return "windowDragArea"
@@ -124,3 +126,12 @@ def content(self):
     @content.setter
     def content(self, value):
         self.__content = value
+
+    # maximizable
+    @property
+    def maximizable(self) -> Optional[bool]:
+        return self._get_attr("maximizable", data_type="bool", def_value=True)
+
+    @maximizable.setter
+    def maximizable(self, value: Optional[bool]):
+        self._set_attr("maximizable", value)