Btukfyl

I am trying to create a custom Lint check so that particular annotated methods have to first ensure that the fragment/activity is attached/visible before doing any work.

E.g.

class MyFragment extends Fragment {



    @CheckIsActive

    void lint_fail() {

        // This would throw a lint warning

    }



    @CheckIsActive

    void lint_succeed() {

        if(isAdded()) {

            // This wouldn't throw a lint warning

        }

    }



}

To do this, I have created an IssueRegistry, the @CheckIsActive annotation and the following custom Detector class.

public class CheckActiveDetector extends Detector implements Detector.UastScanner {



    private static final String CHECK_ACTIVE_ANNOTATION = Constants.ANNOTATIONS_PREFIX + "CheckIsActive";



    private static final Implementation IMPLEMENTATION = new Implementation(

            CheckActiveDetector.class,

            Scope.JAVA_FILE_SCOPE);



    public static final Issue ISSUE = Issue.create(

            "CheckActive",

            "Method should check if the activity/fragment is active",

            "This method should ensure the Activity/Fragment is active before continuing",

            Category.CORRECTNESS,

            9,

            Severity.WARNING,

            IMPLEMENTATION

    );





    public CheckActiveDetector() {}



    @Nullable

    @Override

    public List<Class<? extends UElement>> getApplicableUastTypes() {

        return Collections.<Class<? extends UElement>>singletonList(UMethod.class);

    }



    @Nullable

    @Override

    public UElementHandler createUastHandler(@NotNull final JavaContext context) {

        return new UElementHandler() {

            @Override

            public void visitMethod(@NotNull UMethod node) {





                UExpression body = node.getUastBody();

                if(body != null && node.findAnnotation(CHECK_ACTIVE_ANNOTATION) != null) {



                    String methodName = node.getName();

                    String message = "Overriding method should call `isAdded()"

                            + methodName + "`";

                    Location location = context.getLocation(node);

                    context.report(ISSUE, node, location, message);



                }

            }

        };

    }

}

I have struggled to work out how to progress from the state I am in now, which is (I believe) entering a method and correctly checking if it was annotated. I am not sure with the detector methods, how to

1. Check if the containing class extends Activity / Fragment


2. Check if isAdded() for Fragment or isDestroyed() for Activity was called

Does anyone have any idea how to carry on from this or know where any of this is documented? It seems Google is not using the latest lint version within their source (e.g. CallSuper source) so that has not been too much help.

Thanks

I suspect the actual Lint rule will be very complicated, but in very simple case it can be implemented this way:

@Override

public void visitMethod(@NotNull UMethod node) {

    if (node.findAnnotation(CHECK_ACTIVE_ANNOTATION) == null) {

        return;

    }

    UExpression body = node.getUastBody();

    if (!(body instanceof UBlockExpression)) {

        return;

    }

    List<UExpression> expressions = ((UBlockExpression) body).getExpressions();

    UExpression firstExpression = expressions.get(0);

    // check if the first expression in method body is 'if' expression

    if (!(firstExpression instanceof UIfExpression)) {

        // probably it is not okay

        return;

    }

    UExpression condition = ((UIfExpression) firstExpression).getCondition();

    if (!(condition instanceof UCallExpression)) {

        // isAdded() is a method call, so we need a UCallExpression

        // probably not ok

        return;

    }

    if ("isAdded".equals(((UCallExpression) condition).getMethodName())) {

        // it is ok



        // you can also check argument count and the owner of the method to

        // ensure it is the correct one

    } else {

        // it is not ok

    }

}