UE4运用C++和框架开发坦克大战教程笔记（十九）（第58~60集）完结

58. 弹窗显示与隐藏

这节课我们先来补全 TransferMask() 里对于 Overlay 布局类型面板的遮罩转移逻辑，大体上与 Canvas 布局类型的差不多。

接下来就是编写弹窗的隐藏和重新显示的逻辑。

在写重新显示弹窗的逻辑时我们发现 DoEnterUIPanel() 有一段代码可以复用，但是发现了一处逻辑上的错误，所以要调整一下代码。

DDFrameWidget.cpp

void UDDFrameWidget::DoEnterUIPanel(FName PanelName)
{
   
	// ... 省略
	
		// 此处作更改	
		if (!WorkLayout) {
   
			if (UnActiveCanvas.Num() == 0) {
   
				WorkLayout = WidgetTree->ConstructWidget<UCanvasPanel>(UCanvasPanel::StaticClass());
				WorkLayout->SetVisibility(ESlateVisibility::SelfHitTestInvisible);
			}
			else
				WorkLayout = UnActiveCanvas.Pop();
				
			// 添加布局控件到界面最顶层
			UCanvasPanelSlot* FrameCanvasSlot = RootCanvas->AddChildToCanvas(WorkLayout);
			FrameCanvasSlot->SetAnchors(FAnchors(0.f, 0.f, 1.f, 1.f));
			FrameCanvasSlot->SetOffsets(FMargin(0.f, 0.f, 0.f, 0.f));
			// 添加到激活画布组
			ActiveCanvas.Push(WorkLayout);	
		}

		// ... 省略

		// 此处作更改
		if (!WorkLayout) {
   
			if (UnActiveOverlay.Num() == 0) {
   
				WorkLayout = WidgetTree->ConstructWidget<UOverlay>(UOverlay::StaticClass());
				WorkLayout->SetVisibility(ESlateVisibility::SelfHitTestInvisible);
			}
			else
				WorkLayout = UnActiveOverlay.Pop();

			// 添加布局控件到界面最顶层
			UCanvasPanelSlot* FrameCanvasSlot = RootCanvas->AddChildToCanvas(WorkLayout);
			FrameCanvasSlot->SetAnchors(FAnchors(0.f, 0.f, 1.f, 1.f));
			FrameCanvasSlot->SetOffsets(FMargin(0.f, 0.f, 0.f, 0.f));
			// 添加到激活画布组
			ActiveOverlay.Push(WorkLayout);	
		}

	// ... 省略
}

void UDDFrameWidget::HidePanelReverse(UDDPanelWidget* PanelWidget)
{
   
	// 获取弹窗栈到数组
	TArray<UDDPanelWidget*> PopStack;
	PopPanelStack.GenerateValueArray(PopStack);

	// 如果不是最上层的弹窗，直接返回
	if (PopStack[PopStack.Num() - 1] != PanelWidget) {
   
		DDH::Debug() << PanelWidget->GetObjectName() << " Is Not Last Panel In PopPanelStack" << DDH::Endl();
		return;
	}

	// 从栈中移除
	PopPanelStack.Remove(PanelWidget->GetObjectName());
	// 执行隐藏函数
	PanelWidget->PanelHidden();

	// 调整弹窗栈
	PopStack.Pop();
	if (PopStack.Num() > 0) {
   
		UDDPanelWidget* PrePanelWidget = PopStack[PopStack.Num() - 1];
		// 转移遮罩到新的最顶层的弹窗的下一层
		TransferMask(PrePanelWidget);
		// 恢复被冻结的最顶层的弹窗
		PrePanelWidget->PanelResume();
	}
	// 如果没有弹窗就移除遮罩
	else
		RemoveMaskPanel();
}

void UDDFrameWidget::ShowPanelReverse(UDDPanelWidget* PanelWidget)
{
   
	// 如果弹窗栈里有元素，冻结最顶层的弹窗
	if (PopPanelStack.Num() > 0) {
   
		TArray<UDDPanelWidget*> PanelStack;
		PopPanelStack.GenerateValueArray(PanelStack);
		PanelStack[PanelStack.Num() - 1]->PanelFreeze();
	}

	// 弹窗对象必须从当前父控件移除，再重新添加到最顶层的界面（因为弹窗只是隐藏而不是销毁了）
	if (PanelWidget->UINature.LayoutType == ELayoutType::Canvas) {
   
		UCanvasPanel* PreWorkLayout = Cast<UCanvasPanel>(PanelWidget->GetParent());
		UCanvasPanelSlot* PrePanelSlot = Cast<UCanvasPanelSlot>(PanelWidget->Slot);
		FAnchors PreAnchors = PrePanelSlot->GetAnchors();
		FMargin PreOffsets = PrePanelSlot->GetOffsets();

		// 将 PanelWidget 从当前父控件移除
		PanelWidget->RemoveFromParent();
		// 处理父控件
		if (PreWorkLayout->GetChildrenCount() == 0) {
   
			PreWorkLayout->RemoveFromParent();
			ActiveCanvas.Remove(PreWorkLayout);
			UnActiveCanvas.Push(PreWorkLayout);
		}

		// 寻找最顶层的 WorkLayout
		UCanvasPanel* WorkLayout = NULL;

		// 判断最底层的布局控件是否是 Canvas
		if (RootCanvas->GetChildrenCount() > 0)
			WorkLayout = Cast<UCanvasPanel>(RootCanvas->GetChildAt(RootCanvas->GetChildrenCount() - 1));
			
		if (!WorkLayout) {
   
			// 如果没有任何对象
			if (UnActiveCanvas.Num() == 0) {
   
				WorkLayout = WidgetTree->ConstructWidget<UCanvasPanel>(UCanvasPanel::StaticClass());
				WorkLayout->SetVisibility(ESlateVisibility::SelfHitTestInvisible);
			}
			else
				WorkLayout = UnActiveCanvas.Pop();

			// 添加布局控件到界面最顶层
			UCanvasPanelSlot* FrameCanvasSlot = RootCanvas->AddChildToCanvas(WorkLayout);
			FrameCanvasSlot->SetAnchors