From a0ff84f896af72f34218f829fd321ec90c2dc1ed Mon Sep 17 00:00:00 2001
From: jrfeng <jrfeng331@qq.com>
Date: Sat, 21 Nov 2020 10:44:17 +0800
Subject: [PATCH] feature: add 'OnSelectCountChangeListener'

---
 .../helper/SelectableAdapter.java             |  9 +++++
 .../recyclerview/helper/SelectableHelper.java | 33 +++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/helper/src/main/java/recyclerview/helper/SelectableAdapter.java b/helper/src/main/java/recyclerview/helper/SelectableAdapter.java
index b429d66..50652fa 100644
--- a/helper/src/main/java/recyclerview/helper/SelectableAdapter.java
+++ b/helper/src/main/java/recyclerview/helper/SelectableAdapter.java
@@ -78,6 +78,15 @@ public void setSelectMode(SelectableHelper.SelectMode mode) {
         mSelectableHelper.setSelectMode(mode);
     }
 
+    /**
+     * 设置一个用于监听 “选中数量” 改变的监听器。
+     *
+     * @param listener 监听器，可为 null。为 null 时将清除上次设置的监听器。
+     */
+    public void setOnSelectCountChangeListener(SelectableHelper.OnSelectCountChangeListener listener) {
+        mSelectableHelper.setOnSelectCountChangeListener(listener);
+    }
+
     /**
      * 查询某个列表项是否已被选中。
      *
diff --git a/helper/src/main/java/recyclerview/helper/SelectableHelper.java b/helper/src/main/java/recyclerview/helper/SelectableHelper.java
index 6edcd0f..c80adc6 100644
--- a/helper/src/main/java/recyclerview/helper/SelectableHelper.java
+++ b/helper/src/main/java/recyclerview/helper/SelectableHelper.java
@@ -61,6 +61,7 @@ public class SelectableHelper {
     private List<Integer> mSelectedPositions;
 
     private RecyclerView.AdapterDataObserver mAdapterDataObserver;
+    private OnSelectCountChangeListener mOnSelectCountChangeListener;
 
     public SelectableHelper(@NonNull RecyclerView.Adapter adapter) {
         NonNullUtil.requireNonNull(adapter);
@@ -135,6 +136,16 @@ public void clearSelected() {
         for (Integer selectedPosition : mSelectedPositions.subList(0, mSelectedPositions.size())) {
             deselect(selectedPosition);
         }
+        notifySelectCountChanged();
+    }
+
+    /**
+     * 设置一个用于监听 “选中数量” 改变的监听器。
+     *
+     * @param listener 监听器，可为 null。为 null 时将清除上次设置的监听器。
+     */
+    public void setOnSelectCountChangeListener(@Nullable OnSelectCountChangeListener listener) {
+        mOnSelectCountChangeListener = listener;
     }
 
     /**
@@ -206,6 +217,8 @@ public void onItemRangeRemoved(int positionStart, int itemCount) {
                         mSelectedPositions.add(selectedItem - itemCount);
                     }
                 }
+
+                notifySelectCountChanged();
             }
 
             @Override
@@ -268,6 +281,7 @@ private void select(int position) {
         }
 
         mSelectedPositions.add(position);
+        notifySelectCountChanged();
 
         if (mRecyclerView == null) {
             return;
@@ -287,6 +301,7 @@ private void deselect(int position) {
 
         // 要手动装箱, 否则调用的是 remove(int):E 方法, 而不是 remove(Object):boolean 方法
         mSelectedPositions.remove(Integer.valueOf(position));
+        notifySelectCountChanged();
 
         if (mRecyclerView == null) {
             return;
@@ -301,6 +316,12 @@ private void deselect(int position) {
         }
     }
 
+    private void notifySelectCountChanged() {
+        if (mOnSelectCountChangeListener != null) {
+            mOnSelectCountChangeListener.onSelectCountChanged(mSelectedPositions.size());
+        }
+    }
+
     /**
      * 选择模式。
      */
@@ -320,4 +341,16 @@ public interface Selectable {
 
         void onUnselected();
     }
+
+    /**
+     * 监听选中数量改变的。
+     */
+    public interface OnSelectCountChangeListener {
+        /**
+         * 当选中的列表项的数量发生改变时会回调该方法。
+         *
+         * @param selectedCount 当前的选中数量
+         */
+        void onSelectCountChanged(int selectedCount);
+    }
 }