Use StaggeredGridLayoutManager for gallery thumb list

app/src/main/java/com/hippo/widget/recyclerview/AutoGridLayoutManager.java

@@ -0,0 +1,126 @@
+/*
+ * Copyright 2016 Hippo Seven
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.hippo.widget.recyclerview;
+
+import android.content.Context;
+import android.support.v7.widget.GridLayoutManager;
+import android.support.v7.widget.RecyclerView;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class AutoGridLayoutManager extends GridLayoutManager {
+
+    public static final int STRATEGY_MIN_SIZE = 0;
+    public static final int STRATEGY_SUITABLE_SIZE = 1;
+
+    private int mColumnSize = -1;
+    private boolean mColumnSizeChanged = true;
+    private int mStrategy;
+
+    private List<OnUpdateSpanCountListener> mListeners;
+
+    public AutoGridLayoutManager(Context context, int columnSize) {
+        super(context, 1);
+        setColumnSize(columnSize);
+    }
+
+    public AutoGridLayoutManager(Context context, int columnSize, int orientation, boolean reverseLayout) {
+        super(context, 1, orientation, reverseLayout);
+        setColumnSize(columnSize);
+    }
+
+    public void setColumnSize(int columnSize) {
+        if (columnSize == mColumnSize) {
+            return;
+        }
+        mColumnSize = columnSize;
+        mColumnSizeChanged = true;
+    }
+
+    public void setStrategy(int strategy) {
+        if (strategy == mStrategy) {
+            return;
+        }
+        mStrategy = strategy;
+        mColumnSizeChanged = true;
+    }
+
+    public static int getSpanCountForSuitableSize(int total, int single) {
+        int span = total / single;
+        if (span <= 0) {
+            return 1;
+        }
+        int span2 = span + 1;
+        float deviation = Math.abs(1 - (total / span / (float) single));
+        float deviation2 = Math.abs(1 - (total / span2 / (float) single));
+        return deviation < deviation2 ? span : span2;
+    }
+
+    public static int getSpanCountForMinSize(int total, int single) {
+        return Math.max(1, total / single);
+    }
+
+    @Override
+    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
+        if (mColumnSizeChanged && mColumnSize > 0) {
+            int totalSpace;
+            if (getOrientation() == VERTICAL) {
+                totalSpace = getWidth() - getPaddingRight() - getPaddingLeft();
+            } else {
+                totalSpace = getHeight() - getPaddingTop() - getPaddingBottom();
+            }
+
+            int spanCount;
+            switch (mStrategy) {
+                default:
+                case STRATEGY_MIN_SIZE:
+                    spanCount = getSpanCountForMinSize(totalSpace, mColumnSize);
+                    break;
+                case STRATEGY_SUITABLE_SIZE:
+                    spanCount = getSpanCountForSuitableSize(totalSpace, mColumnSize);
+                    break;
+            }
+            setSpanCount(spanCount);
+            mColumnSizeChanged = false;
+
+            if (null != mListeners) {
+                for (int i = 0, n = mListeners.size(); i < n; i++) {
+                    mListeners.get(i).onUpdateSpanCount(spanCount);
+                }
+            }
+        }
+        super.onLayoutChildren(recycler, state);
+    }
+
+    public void addOnUpdateSpanCountListener(OnUpdateSpanCountListener listener) {
+        if (null == mListeners) {
+            mListeners = new ArrayList<>();
+        }
+        mListeners.add(listener);
+    }
+
+    public void removeOnUpdateSpanCountListener(OnUpdateSpanCountListener listener) {
+        if (null != mListeners) {
+            mListeners.remove(listener);
+        }
+    }
+
+    public interface OnUpdateSpanCountListener {
+        void onUpdateSpanCount(int spanCount);
+    }
+}