onForward property
The animation starts callback, indicating that the dialog is about to open; if you use custom or multiple AnimationControllers, the animation should be run using forward() in this callback
动画开始回调, 表示该dialog即将打开; 如果使用自定义或多个AnimationController时, 应该在此回调中使用forward()运行动画
Implementation
VoidCallback? onForward;