I am working on a Blackberry application which includes Zoom pinch functionality, but this functionality works in touch screen devices. My app will work on curve type of devices too.
Please let me know if "I can detect programmatically if the device is touch screen or not" so I can make my application flexible for both types.
If you only need to support OS 4.7+ devices, then you don't need to use the preprocessor. You can programmatically test for the touchscreen with this:
boolean isTouch = TouchScreen.isSupported();
What Rupak suggested in his answer may not be enough (just adding touch handling code, which will be ignored for non-touch devices). In your case, if you want to support a zoom feature, you may need to actively detect a non-touch device (with the code above), and choose to add a new zoom ButtonField, which is not even shown on touch devices that do support the pinch gesture. If you don't do this, then either non-touch devices won't be able to zoom, or touch devices will have their screens cluttered with an unnecessary button.
But, the TouchScreen API is only for 4.7+. If you need to run the same code on older OS versions, too, this other method can be used:
boolean isTouch = (new Canvas(){protected void paint(Graphics graphics){}}).hasPointerEvents();
My apps mostly still do support 4.5+, which can't even compile touch handling code. So, I normally rely on this kind of preprocessor macro to selectively compile different code. First, at the top of the file
//#preprocess
Then, anywhere inside the file:
//#ifndef TOUCH_SCREEN
/*
//#endif
// code only for touch devices:
import net.rim.device.api.ui.TouchEvent;
//#ifndef TOUCH_SCREEN
*/
//#endif
And then for builds that I will produce for deployment to touchscreen devices, I add the TOUCH_SCREEN preprocessor flag. If you don't want to worry about uploading different app bundles for touch vs. non-touch devices, just programmatically detect touch screens with the Java code (isTouch) and use the preprocessor just to remove code that won't compile on pre-4.7 OS versions.
Note: this somewhat confusing "double negative" preprocessor logic is not a mistake. It's like that to accommodate the slightly different way preprocessors in BlackBerry-enabled IDEs (e.g. JDE, Eclipse, Netbeans) handle preprocessing. Unfortunately, preprocessing is not a standardized J2ME feature, so it's implementation is a little flaky.
Touch support was added since BlackBerry API 4.7.0. Check the documentation of TouchEvent class.
So if you are building application for devices running on 4.7.0 or later, you don't need to do anything. You can code touch event related task and the application will run on both touch and non-touch devices. For non-touch devices the code related to touch event will not executed.
But if you need to support older devices those are running below 4.7.0 you need use preprocessor directives.
Try following link for using preprocessor directives on you application:
Coding for Multiple Blackberry Devices - Using Preprocessor Directives in Eclipse
Other related links:
Create preprocessor directives for a workspace
Specifying preprocessor directives
Preprocessor directives supported by the RIM compiler
Using preprocessor directives in BlackBerry JDE plugin for eclipse?
How To - Use the preprocessor in BlackBerry JDE
