Photo Picker Dialog: Add caching for the decoded images.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java

Index: chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java b/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
index 6c73972eadb3c87da1d3b42c7a18259e2ac6809e..cbe9d7b7c031065d787725ee3ddae002aeabe7f7 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
@@ -6,10 +6,12 @@ package org.chromium.chrome.browser.photo_picker;
 
 import android.app.Activity;
 import android.content.Context;
+import android.graphics.Bitmap;
 import android.graphics.Rect;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.Toolbar.OnMenuItemClickListener;
+import android.util.LruCache;
 import android.view.LayoutInflater;
 import android.view.MenuItem;
 import android.view.View;
@@ -28,6 +30,8 @@ import java.util.List;
  */
 public class PickerCategoryView extends RelativeLayout
         implements FileEnumWorkerTask.FilesEnumeratedCallback, OnMenuItemClickListener {
+    private static final int KILOBYTE = 1024;
+
     // The dialog that owns us.
     private PhotoPickerDialog mDialog;
 
@@ -55,6 +59,14 @@ public class PickerCategoryView extends RelativeLayout
     // The {@link SelectionDelegate} keeping track of which images are selected.
     private SelectionDelegate<PickerBitmap> mSelectionDelegate;
 
+    // A low-resolution cache for images. Helpful for cache misses from the high-resolution cache
+    // to avoid showing gray squares (we show pixelated versions instead until image can be loaded
+    // off disk, which is much less jarring).
+    private LruCache<String, Bitmap> mLowResBitmaps;
+
+    // A high-resolution cache for images.
+    private LruCache<String, Bitmap> mHighResBitmaps;

[Michael van Ouwerkerk, 2017/04/27 17:07:35]

What guarantee do we have that these caches do not survive for longer than
needed?

[Finnur, 2017/05/04 16:05:15]

This object is destroyed when the dialog goes away.

+
     /**
      * The number of columns to show. Note: mColumns and mPadding (see below) should both be even
      * numbers or both odd, not a mix (the column padding will not be of uniform thickness if they
@@ -106,7 +118,22 @@ public class PickerCategoryView extends RelativeLayout
         mRecyclerView.setLayoutManager(mLayoutManager);
         mRecyclerView.addItemDecoration(new GridSpacingItemDecoration(mColumns, mPadding));
 
-        // TODO(finnur): Implement caching.
+        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / KILOBYTE);
+        final int cacheSizeLarge = maxMemory / 2; // 1/2 of the available memory.
+        final int cacheSizeSmall = maxMemory / 8; // 1/8th of the available memory.
+        mLowResBitmaps = new LruCache<String, Bitmap>(cacheSizeSmall) {
+            @Override
+            protected int sizeOf(String key, Bitmap bitmap) {
+                return bitmap.getByteCount() / KILOBYTE;
+            }
+        };
+        mHighResBitmaps = new LruCache<String, Bitmap>(cacheSizeLarge) {

[Michael van Ouwerkerk, 2017/04/27 17:07:35]

Please ping memory-dev@chromium.org
https://groups.google.com/a/chromium.org/forum/#!forum/memory-dev to discuss
whether this use case merits hooking into ComponentCallbacks2.onTrimMemory
https://developer.android.com/reference/android/content/ComponentCallbacks2.html

[Finnur, 2017/05/04 16:05:15]

Will do, thanks.

+            @Override
+            protected int sizeOf(String key, Bitmap bitmap) {
+                return bitmap.getByteCount() / KILOBYTE;
+            }
+        };
+
         // TODO(finnur): Remove this once the decoder service is in place.
         prepareBitmaps();
     }
@@ -176,6 +203,14 @@ public class PickerCategoryView extends RelativeLayout
         return mPickerBitmaps;
     }
 
+    public LruCache<String, Bitmap> getLowResBitmaps() {
+        return mLowResBitmaps;
+    }
+
+    public LruCache<String, Bitmap> getHighResBitmaps() {
+        return mHighResBitmaps;
+    }
+
     public boolean isMultiSelectAllowed() {
         return mMultiSelectionAllowed;
     }