[macos] Implement center method #59

Author: lijy91

example/lib/pages/home.dart

@@ -222,6 +222,12 @@ class _HomePageState extends State<HomePage> with WindowListener {
                 );
               },
             ),
+            PreferenceListItem(
+              title: Text('center'),
+              onTap: () async {
+                await windowManager.center();
+              },
+            ),
             PreferenceListItem(
               title: Text('getPosition / setPosition'),
               accessoryView: Row(

lib/src/window_manager.dart

@@ -204,6 +204,23 @@ class WindowManager {
     return Offset(resultData['x'], resultData['y']);
   }
 
+  // Moves window to the center of the screen.
+  Future<void> center() async {
+    Size windowSize = await getSize();
+    Map<String, dynamic> primaryDisplay = await _getPrimaryDisplay();
+    print(primaryDisplay);
+
+    num visibleWidth = primaryDisplay['visibleSize']['width'];
+    num visibleHeight = primaryDisplay['visibleSize']['height'];
+
+    Offset position = Offset(
+      (visibleWidth / 2) - (windowSize.width / 2),
+      (visibleHeight / 2) - (windowSize.height / 2),
+    );
+
+    await this.setPosition(position);
+  }
+
   /// Moves window to position.
   Future<void> setPosition(Offset position, {animate = false}) async {
     final Map<String, dynamic> arguments = {
@@ -424,6 +441,15 @@ class WindowManager {
     await _channel.invokeMethod('startDragging');
   }
 
+  Future<Map<String, dynamic>> _getPrimaryDisplay() async {
+    final Map<String, dynamic> arguments = {
+      'devicePixelRatio': window.devicePixelRatio,
+    };
+    final Map<dynamic, dynamic> resultData =
+        await _channel.invokeMethod('getPrimaryDisplay', arguments);
+    return Map<String, dynamic>.from(resultData);
+  }
+
   Future<bool> isSubWindow() async {
     return await _channel.invokeMethod('isSubWindow');
   }

macos/Classes/WindowManager.swift

@@ -407,6 +407,32 @@ public class WindowManager: NSObject, NSWindowDelegate {
         }
     }
 
+    public func getPrimaryDisplay() -> NSDictionary {
+        let screen = NSScreen.main!
+        let size: NSDictionary = [
+            "width": screen.frame.width,
+            "height": screen.frame.height,
+        ]
+        let visiblePosition: NSDictionary = [
+            "x": screen.visibleFrame.topLeft.x,
+            "y": screen.visibleFrame.topLeft.y,
+            "width": screen.visibleFrame.width,
+            "height": screen.visibleFrame.height,
+        ]
+        let visibleSize: NSDictionary = [
+            "x": screen.visibleFrame.topLeft.x,
+            "y": screen.visibleFrame.topLeft.y,
+            "width": screen.visibleFrame.width,
+            "height": screen.visibleFrame.height,
+        ]
+        let dict: NSDictionary = [
+            "size": size,
+            "visiblePosition": visiblePosition,
+            "visibleSize": visibleSize,
+        ]
+        return dict;
+    }
+    
     public func isSubWindow() -> Bool {
         let identifier: String = mainWindow.identifier?.rawValue ?? "";
         return identifier == "subwindow"

macos/Classes/WindowManagerPlugin.swift

@@ -209,6 +209,9 @@ public class WindowManagerPlugin: NSObject, FlutterPlugin {
             windowManager.startDragging()
             result(true)
             break
+        case "getPrimaryDisplay":
+            result(windowManager.getPrimaryDisplay())
+            break
         case "isSubWindow":
             result(windowManager.isSubWindow())
             break