Recycling taskViews instead of inflating & throwing them away everytime

Bug: 122345781
Change-Id: If86d22729a42b8d5200f24dbf37a568fb9b11a5b

src/com/android/launcher3/util/ViewPool.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.android.launcher3.util;
+
+import android.content.Context;
+import android.os.Handler;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import com.android.launcher3.util.ViewPool.Reusable;
+
+import androidx.annotation.AnyThread;
+import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
+
+/**
+ * Utility class to maintain a pool of reusable views.
+ * During initialization, views are inflated on the background thread.
+ */
+public class ViewPool<T extends View & Reusable> {
+
+    private final Object[] mPool;
+
+    private final LayoutInflater mInflater;
+    private final ViewGroup mParent;
+    private final int mLayoutId;
+
+    private int mCurrentSize = 0;
+
+    public ViewPool(Context context, @Nullable ViewGroup parent,
+            int layoutId, int maxSize, int initialSize) {
+        mLayoutId = layoutId;
+        mParent = parent;
+        mInflater = LayoutInflater.from(context);
+        mPool = new Object[maxSize];
+
+        if (initialSize > 0) {
+            initPool(initialSize);
+        }
+    }
+
+    @UiThread
+    private void initPool(int initialSize) {
+        Preconditions.assertUIThread();
+        Handler handler = new Handler();
+
+        // Inflate views on a non looper thread. This allows us to catch errors like calling
+        // "new Handler()" in constructor easily.
+        new Thread(() -> {
+            for (int i = 0; i < initialSize; i++) {
+                T view = inflateNewView();
+                handler.post(() -> addToPool(view));
+            }
+        }).start();
+    }
+
+    @UiThread
+    public void recycle(T view) {
+        Preconditions.assertUIThread();
+        view.onRecycle();
+        addToPool(view);
+    }
+
+    @UiThread
+    private void addToPool(T view) {
+        Preconditions.assertUIThread();
+        if (mCurrentSize >= mPool.length) {
+            // pool is full
+            return;
+        }
+
+        mPool[mCurrentSize] = view;
+        mCurrentSize++;
+    }
+
+    @UiThread
+    public T getView() {
+        Preconditions.assertUIThread();
+        if (mCurrentSize > 0) {
+            mCurrentSize--;
+            return (T) mPool[mCurrentSize];
+        }
+        return inflateNewView();
+    }
+
+    @AnyThread
+    private T inflateNewView() {
+        return (T) mInflater.inflate(mLayoutId, mParent, false);
+    }
+
+    /**
+     * Interface to indicate that a view is reusable
+     */
+    public interface Reusable {
+
+        /**
+         * Called when a view is recycled / added back to the pool
+         */
+        void onRecycle();
+    }
+}