i want my Bitmap that has the height of the screen and has a bigger width than the screen to be moved a little bit to the right or left if the user changes the desktop so he
You get exact pixel values via the variables xPixels and yPixels in onOffsetsChanged(). See my answer here: android live wallpaper rescaling
For example, in onOffsetsChanged(), you can set a private class variable
mPixels = xPixels;
Then, in your draw routine
holder = getSurfaceHolder();
c = holder.lockCanvas();
c.translate(mPixels, 0f);
// c.drawBitmap ... goes here :-)
Typically, you will want a bitmap twice the width of your screen, with your artwork centered in the middle. For example: 320 pixel width screen -> 640 pixel width bitmap with "center" from 160 to 480. mPixels will be 0 at the left most launcher screen (of 5), -160 at the center, and -320 at the rightmost screen.