DrKLO/Telegram · error · IllegalStateException

{positionDescription}: Class is not a LayoutManager {classNa

Error message

{positionDescription}: Class is not a LayoutManager {className}

What it means

The class named by app:layoutManager loads and instantiates, but is not a subclass of RecyclerView.LayoutManager (the earlier asSubclass(LayoutManager.class) succeeded via the typed path, yet a ClassCastException surfaces during newInstance/setLayoutManager). RecyclerView reports 'Class is not a LayoutManager'.

Source

Thrown at TMessagesProj/src/main/java/androidx/recyclerview/widget/RecyclerView.java:883

                                    + ": Error creating LayoutManager " + className, e1);
                        }
                    }
                    constructor.setAccessible(true);
                    setLayoutManager(constructor.newInstance(constructorArgs));
                } catch (ClassNotFoundException e) {
                    throw new IllegalStateException(attrs.getPositionDescription()
                            + ": Unable to find LayoutManager " + className, e);
                } catch (InvocationTargetException e) {
                    throw new IllegalStateException(attrs.getPositionDescription()
                            + ": Could not instantiate the LayoutManager: " + className, e);
                } catch (InstantiationException e) {
                    throw new IllegalStateException(attrs.getPositionDescription()
                            + ": Could not instantiate the LayoutManager: " + className, e);
                } catch (IllegalAccessException e) {
                    throw new IllegalStateException(attrs.getPositionDescription()
                            + ": Cannot access non-public constructor " + className, e);
                } catch (ClassCastException e) {
                    throw new IllegalStateException(attrs.getPositionDescription()
                            + ": Class is not a LayoutManager " + className, e);
                }
            }
        }
    }

    private String getFullClassName(Context context, String className) {
        if (className.charAt(0) == '.') {
            return context.getPackageName() + className;
        }
        if (className.contains(".")) {
            return className;
        }
        return RecyclerView.class.getPackage().getName() + '.' + className;
    }

    private void initChildrenHelper() {
        mChildHelper = new ChildHelper(new ChildHelper.Callback() {

View on GitHub (pinned to 45ab8f4308)

Solutions

Ensure app:layoutManager names a concrete subclass of RecyclerView.LayoutManager (LinearLayoutManager, GridLayoutManager, StaggeredGridLayoutManager, or your own subclass).
Double-check the FQN against the actual class hierarchy.
If you only need a different view type, that belongs on the item layout / Adapter, not layoutManager.

Example fix

<!-- before -->
<androidx.recyclerview.widget.RecyclerView
    app:layoutManager="com.example.MyRecyclerAdapter"/>

<!-- after -->
<androidx.recyclerview.widget.RecyclerView
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"/>

Defensive patterns

Strategy: type-guard

Validate before calling

static void assertLayoutManager(Class<?> c) {
    if (!RecyclerView.LayoutManager.class.isAssignableFrom(c)) {
        throw new IllegalArgumentException(c.getName() + " is not a LayoutManager");
    }
}

Type guard

static boolean isLayoutManagerClass(Class<?> c) {
    return RecyclerView.LayoutManager.class.isAssignableFrom(c);
}

Try / catch

null

Prevention

Cross-check the layoutManager class FQN against a LayoutManager subclass.
Do not confuse Adapter/ViewHolder class names with LayoutManager.
Add a lint/test that asserts every app:layoutManager resolves to a LayoutManager subclass.

When it happens

Trigger: app:layoutManager names a class that is NOT a LayoutManager subclass (e.g. a ViewHolder, an Adapter, a plain View). The asSubclass check passed via a different code shape but the assignment to setLayoutManager fails the cast.

Common situations: Confusing the layoutManager attribute with the view class itself. Pasting a class name from a different framework role (Adapter vs LayoutManager).

Related errors

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/c9f8a05f0f61db73. Report an issue: GitHub.