how can move the child only inside the parent?

Recently I worked in a project using Flex. Its a Photo editing project. I have took a Canvas and take a image in that canvas using the code canvas.addChild(image) . Now i can move the image freely by using moving code. The image move inside the canvas and outside the canvas. I 开发者_C百科want to move the image/child only inside the canvas not outside. How can i do this?

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There are two ways to do this:

• Bounding Rectangle
• Scroll Rectangle (or Mask)

Assuming your "moving code" is something like an Event.ENTER_FRAME handler initialized onClick, you want to make it so the image can't leave the bounds of the parent Canvas.

The first case (bounding rectangle) will allow you to drag the image within the retangle but you will always be able to see the whole image. This is how Image croppers work.

To create a bounding rectangle, you'll have to write a fairly detailed method, but the idea behind it is simple. Just get the bounding rectangle from the canvas, and don't let the image.x go below 0 and don't let image.x + image.width go beyond canvas.width. Same with height. Here's a sample Image Cropper in Flex (and the source). Check out how they did it for details.

The second case (scroll rectangle) would allow you to create more of a pan/zoom like container like you see on this Flex Pan/Zoom Map (here's the source). Also, the large image in the Flex Image Cropper on the right is an example of this second case, but they don't have the dragging. That requires that you manipulate the position of the scrollRect property on the canvas. The scrollRect property is a flash.geom.Rectangle defining the Canvas' "viewport". You then change/update the verticalScrollPosition and horizontalScrollPosition properties, so it's backwards (compared to the Bounding Rectangle).

I think if you set clipAndEnableScrolling to true on the canvas, and you drag a child image around inside of it (and image.includeInLayout = true), it should clip the image to only show up inside the canvas. But I'm guessing you want case 1. Just search those properties and you'll find some good examples on google.

Good luck, should be a fun project.

Lance