Question

I wanted to know how I would make a whole symbol (an image) scrollable? I have found out how to do the multi-touch pinch to zoom but I can’t find any code samples that will let me make the image scroll vertically only with one finger.

So all I want to do is make an image scroll up and down with a single finger input. Are there any simple methods or sample code anyone could give me?

Answer 1

There are two ways to make an image scrollable in an AS3 mobile project: using the Pan gesture (two fingers), or using mouse down, move, and up (one finger – touch events are registered as mouse events on mobile devices). The example below supports both.

Note: With the mouse events, you may want to consider adding a timer to differentiate between clicks and drags (shown in example).

// Necessary imports for this example - I use Flash Builder, so I'm not sure what CS5 requires.
import flash.display.DisplayObject;
import flash.events.MouseEvent;
import flash.events.TransformGestureEvent;
import flash.geom.Point;
import flash.ui.Multitouch;
import flash.ui.MultitouchInputMode;
import flash.utils.getTimer;


public class ScrollExample {
    // The image or other display object you want to scroll
    private var t:DisplayObject;
    // Dragging variables
    private var _prevX:Number; // Not required in this case since we're only scrolling vertically
    private var _prevY:Number;
    private var _dragging:Boolean = false;
    private var _lastMouseEvent:int;
    // Minimum touch time to permit drag (in milliseconds) - I use
    private static const MIN_DRAG_TIME:Number = 150;



    public function ScrollExample() {
        // Switch multitouch mode to support gestures (touch/mouse events are still registered)
        Multitouch.inputMode = MultitouchInputMode.GESTURE;

        // For my applications, I have found that the stage is much more responsive to touch events, but you may want to change "stage" here to "t"
        // Pan Gesture - two fingers up and down - like the scroll on a Mac
        stage.addEventListener(TransformGestureEvent.GESTURE_PAN, onPan);
        // Mouse down, move, and up - one finger drag
        stage.addEventListener(MouseEvent.MOUSE_DOWN, onStartDrag);
        stage.addEventListener(MouseEvent.MOUSE_MOVE, onMoveDrag);
        stage.addEventListener(MouseEvent.MOUSE_UP, onStopDrag);
    }


    private function onPan(e:TransformGestureEvent):void {
        // Move target display object by equivalent offset from pan object
        // For only vertical scrolling, don't use X!
        //t.x += e.offsetX;
        t.y += e.offsetY;
    }


    private function onStartDrag(e:MouseEvent):void {
        // Start timer to differentiate between click and drag
        _lastMouseEvent = getTimer();

        // Start dragging
        _dragging = true;
        // Set drag location values to track how drag is occuring
        // For only vertical scrolling, don't use X!
        //_prevX = e.stageX;
        _prevY = e.stageY;
     }


     private function onMoveDrag(e:MouseEvent):void {
         // If mouse down for less than minimum time, don't drag
         if (getTimer() > _lastMouseEvent + MIN_DRAG_TIME && _dragging) {
             // Move target display object to a valid location - prevents scrolling too far
             // Not using X...
             // t.x = ValidXDragPosition(e);
             t.y = ValidYDragPosition(e);

             // Reset drag position values
             _prevX = e.stageX;
             _prevY = e.stageY;
         }
     }


     private function onStopDrag(e:MouseEvent):void {
         // Stop dragging
         _dragging = false;

         // If mouse down time was less than min time, count as click
         if (getTimer() <= _lastMouseEvent + MIN_DRAG_TIME) {
             onClick(e);
         }
     }


     private function onClick(e:MouseEvent):void {
         // Handle your click event here...
     }


     // This function prevents your target display object from moving too far
     // In this example, it stops dragging when the display object boundary is reached
     // (Only showing Y direction)
     private function ValidYDragPosition(e:MouseEvent):Number {
         // Get the requested drag amount
         var requestedPoint:Number = _prevY - e.stageY;

         if (t.y - requestedPoint > 0) {
             // If drag will move target too far down, stop at top of object
             return 0;
         } else if (t.y - requestedPoint < stage.stageHeight - t.height) {
             // If drag will move target too far up, stop at bottom of object
             return stage.stageHeight - t.height;
         } else {
             // Otherwise, allow drag by requested amount
             return t.y - requestedPoint;
         }
     }
 }