NullPointerException from UsbManager

Question

I have some code which looks like

UsbManager usbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
usbManager.getDeviceList();

When I use an Android 5.0 emulator, I get this crash:

java.lang.NullPointerException: Attempt to invoke interface method 'void android.hardware.usb.IUsbManager.getDeviceList(android.os.Bundle)' on a null object reference
    at android.hardware.usb.UsbManager.getDeviceList(UsbManager.java:243)
    ...

I understand that the official Android emulator has no USB support, but I would expect to see an empty list of USB devices rather than a crash.

I peaked in the Android code a bit, and ServiceManager's map of services didn't have an entry for "usb". Nothing in the Android 21 stack seems to handle the null value returned by ServiceManager.

The code works fine on emulated 4.4 devices, but crashes on 5.0 devices. CPU architecture doesn't seem to make a difference; I tried ARM and x86.

It also works fine on all Genymotion devices I've tried, but I need to get this working on CentOS CI hosts, and getting Genymotion to run on CentOS seems to require intrusive changes.

Any ideas for a fix or workaround? As a last resort I could catch UsbManager's NPE, but it would be pretty bad as I also use a third party library which interacts with UsbManager.

Answer 1

https://developer.android.com/reference/android/content/Context.html#getSystemService(java.lang.String)

RETURN Object The service or null if the name does not exist.

As per API, implementation is not obliged to returned a non null value.

Work around: simple.

UsbManager usbManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
if (usbManager == null) {
    Log.w("MyApp","USB Not supported");
    return;
}

// Normal route
usbManager.getDeviceList();

(I have also faced the same issue on Emulator as you described)