The simple answer is: you can not!
The reason is that it is against the law to take a picture without the shutter making sound, this is for privacy concerns. Moreover, as you will notice, you can't take a picture even when your camera preview is not set properly, still for privacy reasons. At this point you have four options:
Find a way to hack the API
Root the phone and disable the shutter sound
Write your own native code for the camera...but this may be highly dependant on the device you're using it
Use the siplest way that is also the way used by most (if not all) the silent camera
applications in the market. Simply intercept the preview frame via the onPreviewFrame callback from your onClickListener and then save it as an image. The major drawback here is that the maximum preview resolution is far less than the maximum picture resolution so the photo you will take this way will have a fairly low resolution. Indeed if you read the comments on the silent camera apps on the market you will see a lot of people complaining about the resolution of the images not being so high. This is the reason why: they use the trick I exaplained you above.
To conclude, there is no easy way to achieve what you want!