juce中的ComponentDragger

這個類其實挺簡單，就是在就是在鼠標移動時更換控件的位置。簡是簡單，用起來挺方便

#ifndef JUCE_COMPONENTDRAGGER_H_INCLUDED
#define JUCE_COMPONENTDRAGGER_H_INCLUDED


//==============================================================================
/**
    An object to take care of the logic for dragging components around with the mouse.

    Very easy to use - in your mouseDown() callback, call startDraggingComponent(),
    then in your mouseDrag() callback, call dragComponent().

    When starting a drag, you can give it a ComponentBoundsConstrainer to use
    to limit the component's position and keep it on-screen.

    e.g. @code
    class MyDraggableComp
    {
        ComponentDragger myDragger;

        void mouseDown (const MouseEvent& e)
        {
            myDragger.startDraggingComponent (this, e);
        }

        void mouseDrag (const MouseEvent& e)
        {
            myDragger.dragComponent (this, e, nullptr);
        }
    };
    @endcode
*/
class JUCE_API  ComponentDragger
{
public:
    //==============================================================================
    /** Creates a ComponentDragger. */
    ComponentDragger();

    /** Destructor. */
    virtual ~ComponentDragger();

    //==============================================================================
    /** Call this from your component's mouseDown() method, to prepare for dragging.

        @param componentToDrag      the component that you want to drag
        @param e                    the mouse event that is triggering the drag
        @see dragComponent
    */
    void startDraggingComponent (Component* componentToDrag,
                                 const MouseEvent& e);

    /** Call this from your mouseDrag() callback to move the component.

        This will move the component, using the given constrainer object to check
        the new position.

        @param componentToDrag      the component that you want to drag
        @param e                    the current mouse-drag event
        @param constrainer          an optional constrainer object that should be used
                                    to apply limits to the component's position. Pass
                                    null if you don't want to contrain the movement.
        @see startDraggingComponent
    */
    void dragComponent (Component* componentToDrag,
                        const MouseEvent& e,
                        ComponentBoundsConstrainer* constrainer);

private:
    //==============================================================================
    Point<int> mouseDownWithinTarget;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (ComponentDragger)
};

#endif   // JUCE_COMPONENTDRAGGER_H_INCLUDED

下面看看拖動部份，可以看來，就是調整位置。

void ComponentDragger::dragComponent (Component* const componentToDrag, const MouseEvent& e,
                                      ComponentBoundsConstrainer* const constrainer)
{
    jassert (componentToDrag != nullptr);
    jassert (e.mods.isAnyMouseButtonDown()); // The event has to be a drag event!

    if (componentToDrag != nullptr)
    {
        Rectangle<int> bounds (componentToDrag->getBounds());

        // If the component is a window, multiple mouse events can get queued while it's in the same position,
        // so their coordinates become wrong after the first one moves the window, so in that case, we'll use
        // the current mouse position instead of the one that the event contains...
        if (componentToDrag->isOnDesktop())
            bounds += componentToDrag->getLocalPoint (nullptr, e.source.getScreenPosition()).roundToInt() - mouseDownWithinTarget;
        else
            bounds += e.getEventRelativeTo (componentToDrag).getPosition() - mouseDownWithinTarget;

        if (constrainer != nullptr)
            constrainer->setBoundsForComponent (componentToDrag, bounds, false, false, false, false);
        else
            componentToDrag->setBounds (bounds);
    }
}