Stetho is a great debugging tool for Android and we have made sure it works with Litho as well. To enable Litho debugging in Stetho, add the following lines in the onCreate() method of your Application implementation.

public class SampleApplication extends Application {
  public void onCreate() {
    SoLoader.init(this, false);
              .enableWebKitInspector(new LithoWebKitInspector(this))

This will enable full integration of Litho in stetho. After you have enabled Litho support, just start your app and navigate to chrome://inspect in your browser.

Stetho start

Click on the inspect link for the application you would like to inspect (we are using the Litho sample app). This opens a UI inspector where you are able to inspect the View and Component hierarchy of your application.

Stetho inspect

When inspecting a Litho component you are also given the ability to edit the contents of your UI directly from the inspector! This enables quick design iterations by tweaking margins, padding, and many other properties, without needed to re-compile or re-start the application. You can also use this to quickly test that your UI handles different lengths of text properly.

Stetho edit

Annotation Processor

With Gradle

Debugging the annotation processor stage is a bit tricky as you are essentially debugging the Java Compiler (javac). Gradle, however, allows you to attach a debugger during the compilation stage by setting the property org.gradle.debug to true. To start Gradle with that flag, figure out a target that invokes the annotation processor and start it like this:

./gradlew --no-daemon -Dorg.gradle.debug=true :litho-widget:compileDebugJavaWithJavac

In this case we are compiling the litho-widget package.

This will pause the execution during the “Starting Daemon” phase until you connect your debugger. This can be done by running a standard “Remote” target in IntelliJ which will look like this:

IntelliJ Remote Target

Now set a breakpoint at the right point, run your remote target and debug away!

With Buck

Buck doesn’t have built-in support for suspending the compiler, but you can still attach a debugger by directly instrumenting the JVM to open a debugging port.

For that, first make sure to kill any previous instances of Buck which may still be running with old flags, then set the JAVA_TOOLS_OPTIONS to contain the JDWP options.

$ buck kill
$ env JAVA_TOOL_OPTIONS="-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005" buck build //litho-widget/...

Note that this won’t pause the JVM (suspend=n), but as the process will continue to run you can choose to attach to the process at any time.

Edit on GitHub