Day 0

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1. SlateCore\SlotBase.h

class SLATECORE_API FSlotBase  // widget槽位, 每个槽位可拥有一个widget实例
{
  FORCEINLINE_DEBUGGABLE void AttachWidget( const TSharedRef<SWidget>& InWidget )
  {
      Widget = InWidget;
  }

  /**
   * Access the widget in the current slot.
   * There will always be a widget in the slot; sometimes it is
   * the SNullWidget instance.
   */
  FORCEINLINE_DEBUGGABLE const TSharedRef<SWidget>& GetWidget() const
  {
      return Widget;
  }

  /**
   * Remove the widget from its current slot.
   * The removed widget is returned so that operations could be performed on it.
   * If the null widget was being stored, an invalid shared ptr is returned instead.
   */
  const TSharedPtr<SWidget> DetachWidget();
private:
  /**
   *
   * Widget IS NOW PRIVATE!
   *
   */
  TSharedRef<SWidget> Widget;
};

template<typename SlotType>
class TSlotBase : public FSlotBase；

问题列表:

• 为何要TSlotBase，FSlotBase的子类是否拥有更多的槽位属性.

2. SlateCore\Public\Widgets\DeclarativeSyntaxSupport.h
   该文件时为了实现声明式编写ui而定义一些宏和类，声明式语法如下

        //The Maximize/Minimize button is only displayed when not in Immersive mode.
        SNew( SEditorViewportToolBarButton )
          .Cursor( EMouseCursor::Default )
          .ButtonType( EUserInterfaceActionType::ToggleButton )
          .IsChecked( ViewportRef, &SLevelViewport::IsMaximized )
          .OnClicked( ViewportRef, &SLevelViewport::OnToggleMaximize )
          .Visibility( ViewportRef, &SLevelViewport::GetMaximizeToggleVisibility )
          .Image( "LevelViewportToolBar.Maximize" )
          .ToolTipText( LOCTEXT("Maximize_ToolTip", "Maximizes or restores this viewport") )

宏定义：

/**
 * Slate widgets are constructed through SNew and SAssignNew.
 * e.g.
 *      
 *     TSharedRef<SButton> MyButton = SNew(SButton);
 *        or
 *     TSharedPtr<SButton> MyButton;
 *     SAssignNew( MyButton, SButton );
 *
 * Using SNew and SAssignNew ensures that widgets are populated
 */

#define SNew( WidgetType, ... ) \
    MakeTDecl<WidgetType>( #WidgetType, __FILE__, __LINE__, RequiredArgs::MakeRequiredArgs(__VA_ARGS__) ) <<= TYPENAME_OUTSIDE_TEMPLATE WidgetType::FArguments()


#define SAssignNew( ExposeAs, WidgetType, ... ) \
    MakeTDecl<WidgetType>( #WidgetType, __FILE__, __LINE__, RequiredArgs::MakeRequiredArgs(__VA_ARGS__) ) . Expose( ExposeAs ) <<= TYPENAME_OUTSIDE_TEMPLATE WidgetType::FArguments()

其中每种类型的Widget都有自己的WidgetType::FArguments，作为初始化新实例的参数。

TDecl封装了构造Widget实例和初始化操作:

/**
 * Utility class used during widget instantiation.
 * Performs widget allocation and construction.
 * Ensures that debug info is set correctly.
 * Returns TSharedRef to widget.
 *
 * @see SNew
 * @see SAssignNew
 */
template<class WidgetType, typename RequiredArgsPayloadType>
struct TDecl
{
    TDecl( const ANSICHAR* InType, const ANSICHAR* InFile, int32 OnLine, RequiredArgsPayloadType&& InRequiredArgs )
        : _Widget( TWidgetAllocator<WidgetType, TIsDerivedFrom<WidgetType, SUserWidget>::IsDerived >::PrivateAllocateWidget() )
        , _RequiredArgs(InRequiredArgs)
    {
        _Widget->SetDebugInfo( InType, InFile, OnLine );
    }

    /**
     * Initialize OutVarToInit with the widget that is being constructed.
     * @see SAssignNew
     */
    template<class ExposeAsWidgetType>
    TDecl& Expose( TSharedPtr<ExposeAsWidgetType>& OutVarToInit )
    {
        OutVarToInit = _Widget;
        return *this;
    }

    /**
     * Initialize OutVarToInit with the widget that is being constructed.
     * @see SAssignNew
     */
    template<class ExposeAsWidgetType>
    TDecl& Expose( TSharedRef<ExposeAsWidgetType>& OutVarToInit )
    {
        OutVarToInit = _Widget;
        return *this;
    }

    /**
     * Initialize a WEAK OutVarToInit with the widget that is being constructed.
     * @see SAssignNew
     */
    template<class ExposeAsWidgetType>
    TDecl& Expose( TWeakPtr<ExposeAsWidgetType>& OutVarToInit )
    {
        OutVarToInit = _Widget;
        return *this;
    }

    /**
     * Complete widget construction from InArgs.
     *
     * @param InArgs  NamedArguments from which to construct the widget.
     *
     * @return A reference to the widget that we constructed.
     */
        // 注意：该重载函数在宏中的应用.
    TSharedRef<WidgetType> operator<<=( const typename WidgetType::FArguments& InArgs ) const
    {
        //@todo UMG: This should be removed in favor of all widgets calling their superclass construct.
        _Widget->SWidgetConstruct(
            InArgs._ToolTipText,
            InArgs._ToolTip ,
            InArgs._Cursor ,
            InArgs._IsEnabled ,
            InArgs._Visibility,
            InArgs._RenderTransform,
            InArgs._RenderTransformPivot,
            InArgs._Tag,
            InArgs._ForceVolatile,
            InArgs._Clipping,
            InArgs.MetaData );

                // 这里传递用户自定义类的参数, 和 FArguments的参数
        _RequiredArgs.CallConstruct(_Widget, InArgs);

        return _Widget;
    }

    const TSharedRef<WidgetType> _Widget;
    RequiredArgsPayloadType& _RequiredArgs;
};

3. SlateCore\Public\Widgets\IToolTip.h
   工具提示接口, 目前还不知道如何使用。

/**
 * Interface for tool tips.
 */
class IToolTip
{
public:

    /**
     * Gets the widget that this tool tip represents.
     *
     * @return The tool tip widget.
     */
    virtual TSharedRef<class SWidget> AsWidget( ) = 0;

    /**
     * Gets the tool tip's content widget.
     *
     * @return The content widget.
     */
    virtual TSharedRef<SWidget> GetContentWidget( ) = 0;

    /**
     * Sets the tool tip's content widget.
     *
     * @param InContentWidget The new content widget to set.
     */
    virtual void SetContentWidget( const TSharedRef<SWidget>& InContentWidget ) = 0;

    /**
     * Checks whether this tool tip has no content to display right now.
     *
     * @return true if the tool tip has no content to display, false otherwise.
     */
    virtual bool IsEmpty( ) const = 0;

    /**
     * Checks whether this tool tip can be made interactive by the user (by holding Ctrl).
     *
     * @return true if it is an interactive tool tip, false otherwise.
     */
    virtual bool IsInteractive( ) const = 0;

    /**
     * Called when the tooltip widget is about to be requested for opening.
     */
    virtual void OnOpening( ) = 0;

    /**
     * Called when the tooltip widget is closed and the tooltip is no longer needed.
     */
    virtual void OnClosed( ) = 0;

public:

    /** Virtual destructor. */
    virtual ~IToolTip( ) { }
};