[Feature] Add FastScrollerBuilder.setPopupTextProvider().

Author: zhanghai

README.md

@@ -52,6 +52,7 @@ You can also implement [`PopupTextProvider`](library/src/main/java/me/zhanghai/a
 For more customization, please use the methods on [`FastScrollerBuilder`](library/src/main/java/me/zhanghai/android/fastscroll/FastScrollerBuilder.java). Namely:
 
 - `setViewHelper()` allows providing a custom `ViewHelper` to support more views.
+- `setPopupTextProvider()` allows providing a custom `PopupTextProvider` if your `RecyclerView.Adapter` cannot implement that interface.
 - `setPadding()` allows setting a custom padding for the scrollbar, instead of the padding of the view.
 - `setTrackDrawable()` and `setThumbDrawable()` allow setting custom drawables for the scrollbar. The `android:state_pressed` state will be updated for them so you can use a selector.
 - `setPopupStyle()` allows customizing the popup view with a lambda that will receive the view.

library/src/main/java/me/zhanghai/android/fastscroll/FastScrollerBuilder.java

@@ -39,6 +39,9 @@ public class FastScrollerBuilder {
     @Nullable
     private FastScroller.ViewHelper mViewHelper;
 
+    @Nullable
+    private PopupTextProvider mPopupTextProvider;
+
     @Nullable
     private Rect mPadding;
 
@@ -65,6 +68,12 @@ public FastScrollerBuilder setViewHelper(@Nullable FastScroller.ViewHelper viewH
         return this;
     }
 
+    @NonNull
+    public FastScrollerBuilder setPopupTextProvider(@Nullable PopupTextProvider popupTextProvider) {
+        mPopupTextProvider = popupTextProvider;
+        return this;
+    }
+
     @NonNull
     public FastScrollerBuilder setPadding(int left, int top, int right, int bottom) {
         if (mPadding == null) {
@@ -147,7 +156,7 @@ private FastScroller.ViewHelper getOrCreateViewHelper() {
         if (mView instanceof ViewHelperProvider) {
             return ((ViewHelperProvider) mView).getViewHelper();
         } else if (mView instanceof RecyclerView) {
-            return new RecyclerViewHelper((RecyclerView) mView);
+            return new RecyclerViewHelper((RecyclerView) mView, mPopupTextProvider);
         } else if (mView instanceof NestedScrollView) {
             throw new UnsupportedOperationException("Please use "
                     + FastScrollNestedScrollView.class.getSimpleName() + " instead of "

library/src/main/java/me/zhanghai/android/fastscroll/RecyclerViewHelper.java

@@ -31,12 +31,16 @@ class RecyclerViewHelper implements FastScroller.ViewHelper {
 
     @NonNull
     private final RecyclerView mView;
+    @Nullable
+    private final PopupTextProvider mPopupTextProvider;
 
     @NonNull
     private final Rect mTempRect = new Rect();
 
-    public RecyclerViewHelper(@NonNull RecyclerView view) {
+    public RecyclerViewHelper(@NonNull RecyclerView view,
+                              @Nullable PopupTextProvider popupTextProvider) {
         mView = view;
+        mPopupTextProvider = popupTextProvider;
     }
 
     @Override
@@ -115,11 +119,16 @@ public void scrollTo(int offset) {
     @Nullable
     @Override
     public String getPopupText() {
-        RecyclerView.Adapter<?> adapter = mView.getAdapter();
-        if (!(adapter instanceof PopupTextProvider)) {
+        PopupTextProvider popupTextProvider = mPopupTextProvider;
+        if (popupTextProvider == null) {
+            RecyclerView.Adapter<?> adapter = mView.getAdapter();
+            if (adapter instanceof PopupTextProvider) {
+                popupTextProvider = (PopupTextProvider) adapter;
+            }
+        }
+        if (popupTextProvider == null) {
             return null;
         }
-        PopupTextProvider popupTextProvider = (PopupTextProvider) adapter;
         int position = getFirstItemAdapterPosition();
         if (position == RecyclerView.NO_POSITION) {
             return null;