how to launch android application by hardware key

the below is one method to launch Android application by one hardware key.
I use "keycodes" in init..rc in this method.

1.make sure "=y" in kernel configuration file.

2.in init..rc, add below lines.
service launch_apk /system/bin/sh /system/bin/launch_apk.sh
    disabled
    oneshot
    keycodes 270
270 is one example of key index.

3.add one script file named launch_apk.sh in /system/bin/.
the context is as below.
    am start com.example.sendintent/com.example.sendintentMainActivity
com.example.sendintent. is one example of Main Activity of the targeted application.

4.in fact, this "keycodes" method is designed to be used in debuggable mode, see below comments in /system/core/init.keychords.c
    // only handle keychords if ro.debuggable is set or adb is enabled.
    // the logic here is that bugreports should be enabled in userdebug or eng builds
    // and on user builds for users that are developers.
so if you want to use this method in the version faced to end-user, you need do walk around here.