Intent intent = new Intent(); //呼叫照相機
intent.setAction("android.media.action.STILL_IMAGE_CAMERA");
startActivity(intent);

Button btn = (Button)findViewById(R.id.button1);
btn.setOnClickListener(new OnClickListener(){

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent intent = new Intent(); //呼叫照相機
intent.setAction("android.media.action.STILL_IMAGE_CAMERA");
startActivity(intent);
}});