What causes "getContext().getString(R.string.banner_adapter_null_error)" in youth5201314/banner?

Create and pass a concrete BannerAdapter/ImageAdapter instance: banner.setAdapter(new ImageAdapter(images)).

youth5201314/banner · error · NullPointerException

getContext().getString(R.string.banner_adapter_null_error)

Error message

getContext().getString(R.string.banner_adapter_null_error)

What it means

Banner.setAdapter() throws this NullPointerException when you pass a null adapter. The banner requires a non-null RecyclerView.Adapter to render its pages, so it fails fast with a localized message (R.string.banner_adapter_null_error) instead of crashing later inside the RecyclerView. It is an explicit guard in the library's public API.

Solutions

Create and pass a concrete BannerAdapter/ImageAdapter instance: banner.setAdapter(new ImageAdapter(images)).
Verify the adapter variable is non-null before calling setAdapter (assert or if-check).
Ensure image/data list is initialized before building the adapter so the adapter itself isn't null.
If an adapter is mandatory, never conditionally skip setAdapter; provide a default empty adapter instead.

Example fix

// before
ImageAdapter adapter = null;
banner.setAdapter(adapter); // NPE
// after
ImageAdapter adapter = new ImageAdapter(imageUrls);
banner.setAdapter(adapter);

Defensive patterns

Strategy: validation

Validate before calling

if (adapter == null) {
    throw new IllegalArgumentException("Banner adapter must not be null");
}
banner.setAdapter(adapter);

Prevention

Always instantiate the adapter immediately before setAdapter.
Never build the adapter from nullable data without a null check.
Keep banner setup code together so no setup step is accidentally skipped.
Fail fast in your own factory methods instead of returning null adapters.

When it happens

Trigger: Calling banner.setAdapter(null) directly, or passing an adapter variable/factory method that returned null (e.g. an adapter not yet initialized, or a conditional adapter construction that fell through).

Common situations: Configuring the banner in an Activity/Fragment before the adapter is created; adapter built from data that is still null; copy-pasted setup code where the setAdapter line was commented out but a variable remained null; dependency-injection factory returning null on failure.

Related errors

AI-assisted analysis of youth5201314/banner@777c7dbfaa (2026-09-08). Data as JSON: /api/errors/6a4fa6011b4c9b6e. Report an issue: GitHub.

Appendix: source

Thrown at banner/src/main/java/com/youth/banner/Banner.java:708

    }

    /**
     * 移除一些引用
     */
    public void destroy() {
        if (getViewPager2() != null && mPageChangeCallback != null) {
            getViewPager2().unregisterOnPageChangeCallback(mPageChangeCallback);
            mPageChangeCallback = null;
        }
        stop();
    }

    /**
     * 设置banner的适配器
     */
    public Banner setAdapter(BA adapter) {
        if (adapter == null) {
            throw new NullPointerException(getContext().getString(R.string.banner_adapter_null_error));
        }
        this.mAdapter = adapter;
        if (!isInfiniteLoop()) {
            getAdapter().setIncreaseCount(0);
        }
        getAdapter().registerAdapterDataObserver(mAdapterDataObserver);
        mViewPager2.setAdapter(adapter);
        setCurrentItem(mStartPosition, false);
        initIndicator();
        return this;
    }

    /**
     * 设置banner的适配器
     * @param adapter
     * @param isInfiniteLoop 是否支持无限循环
     * @return
     */

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