LSPosed is a framework that lets a module change how an app behaves at runtime. A module can hook a method and run extra code before or after the original method. That power is useful for developers who want to test behaviour and build tools for their own apps. It is not a tool for changing apps that belong to other people without permission.
Building a module from scratch sounds complex but the structure is small. A module needs a manifest entry and a hook class and a configuration file that tells LSPosed which apps to target. The hook class uses the Xposed API to find a method and attach code to it. Once that structure works you can build more complex features on top of it.
This guide assumes a rooted test device that you own and an LSPosed installation that you control. It also assumes that you will test only your own apps or apps that you have clear permission to modify. Keep backups before you enable a new module. A bad hook can cause an app to crash in a loop and a backup makes recovery fast.
The module project structure
Start with a normal Android app project in Android Studio. Add the LSPosed API dependency for the version that matches your framework. Create a main hook class that implements the entry point that LSPosed expects. That class receives a startup parameter that tells it which package is loading. Use that parameter to decide whether your hook should run for that app.
Add a configuration file that lists the module scope. The scope controls which apps can see the module. A narrow scope is safer than a broad scope because it limits the effect of a mistake. Test with one target app first and expand the scope only when the hook works reliably for that app.
Keep the module code separate from the app code that you test. A module should not share data with the target app through hidden channels. Use clear logging during development and remove verbose logging before you share a module with anyone. Clear structure makes debugging much easier when a hook does not fire.
Writing your first safe hook
Choose a simple method in your own test app for the first hook. A good first target is a method that returns a string or a number and has no side effects. Hook that method and log the call before the original code runs. Then log the result after the original code runs. That pattern teaches you the hook lifecycle without changing behaviour in a risky way.
Handle errors inside the hook. A hook that throws an exception can crash the target app. Wrap risky code in a try block and log the error instead of letting it escape. A safe hook fails quietly and leaves the original behaviour intact when something goes wrong. That habit protects the test app and it protects your time.
Test the hook with the target app in the foreground and in the background. Some methods run on different threads and some run only during startup. A hook that works during startup may not work for a method that loads later. Note when the method runs and adjust the hook timing if needed.
Hooking constructors and system methods with care
Constructors need extra care because the object does not exist yet when the hook runs. Use the after hook to inspect the created object rather than the before hook to change construction. Changing construction can break invariants that the class depends on. A small change in a constructor can cause failures far away from the hook site.
System methods need even more care. Hooking a system service can affect every app on the device. Start with a narrow target and a simple log hook. Observe the effect on the whole device before you add logic that changes a return value. A system hook that looks harmless in one app can break another app that depends on the same method.
Use the module scope to limit system hooks to test apps when possible. If a system hook must run broadly then test it with several apps and several device states. Record which apps were tested and what behaviour you observed. That record helps you spot a regression after a system update.
Debugging when a hook does not fire
A hook that does not fire usually has a simple cause. The package name may be wrong or the class name may be wrong or the method signature may not match. Check the log for a class not found error or a method not found error. Those errors point directly to the mismatch. Fix the name or the signature and test again.
Obfuscation can change class and method names in a release build. Test hooks against a debug build of your own app first. A debug build keeps names readable and makes hook development much easier. Once the hook works in debug then test it against a release build if that is part of your goal.
LSPosed logs are your best friend during development. Enable module logs and read them after each test run. Look for a load message for your module and a hook success message for your target. A missing load message means a scope or manifest problem. A missing hook message means a name or signature problem.
- Check the package name and class name first.
- Confirm the method signature matches exactly.
- Test against a debug build before a release build.
- Read LSPosed logs after every test run.
Code you can adapt
// Minimal LSPosed hook for a method in your own test app
public class MainHook implements IXposedHookLoadPackage {
@Override
public void handleLoadPackage(XC_LoadPackage.LoadPackageParam lpparam) {
if (!lpparam.packageName.equals("com.example.mytestapp")) return;
XposedHelpers.findAndHookMethod(
"com.example.mytestapp.MainActivity",
lpparam.classLoader,
"getWelcomeMessage",
new XC_MethodHook() {
@Override
protected void afterHookedMethod(MethodHookParam param) {
XposedBridge.log("Hook ran result=" + param.getResult());
}
});
}
}The snippet above is an original example written for this guide. It shows a narrow hook for a test app and it logs the result without changing app behaviour.
The narrow package check at the start is important. Without it the hook code would run for every app that loads. That waste slows the device and it increases the chance of a crash in an unrelated app. Always guard a hook with a package check before you search for a class or a method.
Logging the result helps you confirm that the hook fired and that the original method still ran. Once that confirmation works you can move to more advanced hooks. Change one behaviour at a time and test after each change. A slow and steady method beats a large hook that fails in a confusing way.
How this topic connects to nearby work
Module testing on rooted devices raises the same detection questions covered in the guide to bypass Android root detection.
Module work shares tools and habits with the research methods in the guide to APK modding techniques.
The runtime layer behind many hooks is explained in the guide to ART runtime hooks for developers.
Putting it into practice
Module updates need testing against framework updates because LSPosed versions change hook behaviour over time. A hook that worked on one framework version may behave differently after an update to the runtime or to the module API. Test a module after every framework update on a test device before you share it. Keep a note of the framework version that each module version supports. That note prevents users from installing a module on an unsupported framework version and reporting a confusing failure.
Scope changes after an update also deserve attention. A new target app version may rename a class or change a method signature. A hook that relied on the old name will silently stop working. Add a log entry when a hook attaches successfully and when it fails to find a class. That log entry turns a silent failure into a visible diagnostic. Check those logs after every target app update during development.
A final module check should test the module after a target app update that you did not expect. Target apps update frequently and a hook can break without any change to the module itself. Set a reminder to retest the module after each major target update during development. Log the target version with each test result so a failure can be linked to a specific update. That habit prevents a module from silently stopping work for weeks while users report a confusing failure. Document the supported target version in the module readme so users can check compatibility before they install an update. A clear readme note saves support time for every future target update.
Common mistakes
A common mistake is to hook a method by name without checking the full signature. A class may have several methods with the same name and different parameters. Hooking the wrong overload can cause a crash or a silent failure. Always check parameter types and return type before you write the hook.
Another mistake is to enable a module for all apps during development. A broad scope turns a small error into a device wide problem. Keep the scope narrow until the hook is stable. Expand the scope only with a reason and a test for each new target.
A third mistake is to leave debug logging enabled in a shared module. Verbose logs can leak test data and they slow down the device. Remove or guard verbose logs before you share a module. Keep a clean release version separate from a debug version.
Frequently asked questions
Do I need root to test an LSPosed module?
Yes for a normal LSPosed setup on a test device. LSPosed needs a rooted environment to inject hooks into apps. Use a dedicated test device for this work and keep your daily phone separate from experiments.
Why does my module load but my hook never runs?
Check the package name and the class name and the method signature first. Then check the module scope and the LSPosed logs. A missing log message usually points to a scope problem while a not found error points to a name problem.
Can I hook an app that I do not own?
Only with clear permission for testing or research. Hooking other apps without permission can break terms and can harm users. This guide is for your own apps and for authorised testing only.
Conclusion
A custom LSPosed module starts with a small and safe structure. A narrow scope and a simple hook and clear logs give you a foundation that you can trust. From there you can build tools that help you test and understand your own apps. Keep hooks small and test often and guard every change with error handling.
Your concrete next step is to create the test app and the module project today and hook a single simple method that only logs its result. Confirm that log entry in LSPosed logs. That first success proves the whole setup before you build anything larger.
