如何在Android中的gridview中显示随机图像

I have a number of images in my directory and I'm displaying them in a gridview in Android. I I have set a limit on how many images it displays but I also want those images to be randomly selected. At the moment, the gridview displays the first set of images (e.g. 4). I can come up with the random number generator but I don't know how/why the gridview is selecting the first set of images (e.g. the first 4 images).I have a number of images in my directory and I