UE4 Slate教程4——自定义控件

本文将介绍自定义Slate控件的方法、向控件传递参数的方法，以及SButton事件响应背后的原理。

使用类向导添加一个SCompoundWidget类型的控件，命名为“SCustomWidget”，添加如下代码：
SCustomWidget.h：

#pragma once

#include "CoreMinimal.h"
#include "Widgets/SCompoundWidget.h"
#include "DeclarativeSyntaxSupport.h"

// 声明一个委托
DECLARE_DELEGATE_OneParam(FOnButtonDown, FString)

class HELLOSLATE_API SCustomWidget : public SCompoundWidget
{
public:
	SLATE_BEGIN_ARGS(SCustomWidget)
	{
		_Message = TEXT("Hello");// 这样设置参数的默认值
	}

	// 将要传递的参数放到反射系统，这样就可以在SNew之后为该变量赋值
	SLATE_EVENT(FOnButtonDown, OnButtonDown)
	SLATE_ARGUMENT(FString, Message)

	SLATE_END_ARGS()

	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs);

	// 重写OnMouseButtonDown函数，在这里执行委托
	virtual FReply OnMouseButtonDown(const FGeometry& MyGeometry, const FPointerEvent& MouseEvent) override;

	// 声明要传递的参数
	FOnButtonDown OnButtonDown;
	FString Message;
};

SCustomWidget.cpp：

#include "SCustomWidget.h"
#include "SlateOptMacros.h"

BEGIN_SLATE_FUNCTION_BUILD_OPTIMIZATION
void SCustomWidget::Construct(const FArguments& InArgs)
{
	// 赋予传入的值
	OnButtonDown = InArgs._OnButtonDown;
	Message = InArgs._Message;

	/*
	ChildSlot
	[
		// Populate the widget
	];
	*/
}

FReply SCustomWidget::OnMouseButtonDown(const FGeometry& MyGeometry, const FPointerEvent& MouseEvent)
{
	OnButtonDown.ExecuteIfBound(Message);

	return FReply::Handled();
}
END_SLATE_FUNCTION_BUILD_OPTIMIZATION

在SStandardSlateWidget中构建该控件并传入参数：
SStandardSlateWidget.h：

#pragma once

#include "CoreMinimal.h"
#include "Widgets/SCompoundWidget.h"
#include "DeclarativeSyntaxSupport.h"

class HELLOSLATE_API SStandardSlateWidget : public SCompoundWidget
{
public:
	SLATE_BEGIN_ARGS(SStandardSlateWidget)
	{}
	SLATE_END_ARGS()

	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs);

	// 这个是用来绑定到委托上的函数
	void ShowMessage(FString inMessage);
};

SStandardSlateWidget.cpp：

#include "SStandardSlateWidget.h"
#include "SlateOptMacros.h"

#include "SCustomWidget.h"
#include "MessageDialog.h"

BEGIN_SLATE_FUNCTION_BUILD_OPTIMIZATION
void SStandardSlateWidget::Construct(const FArguments& InArgs)
{	
	ChildSlot
	[
		SNew(SCustomWidget)
		.Message("Hello World!")// 传入普通变量
		.OnButtonDown(this, &SStandardSlateWidget::ShowMessage)// 传入委托
	];
}

void SStandardSlateWidget::ShowMessage(FString inMessage)
{
	FMessageDialog::Open(EAppMsgType::Ok, FText::FromString(inMessage));
}
END_SLATE_FUNCTION_BUILD_OPTIMIZATION

效果如下：

查看SButton的源码，可以看到如下：

		/** Called when the button is clicked */
		SLATE_EVENT( FOnClicked, OnClicked )

		/** Called when the button is pressed */
		SLATE_EVENT( FSimpleDelegate, OnPressed )

		/** Called when the button is released */
		SLATE_EVENT( FSimpleDelegate, OnReleased )

		SLATE_EVENT( FSimpleDelegate, OnHovered )

		SLATE_EVENT( FSimpleDelegate, OnUnhovered )

可以看出，Slate预置的控件均是采用这种方式传递事件。