[Contextual Search] Adds offscreen View rendering capability

ui/android/java/src/org/chromium/ui/resources/dynamics/ViewResourceInflater.java

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.ui.resources.dynamics;
+
+import android.content.Context;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.ViewTreeObserver;
+
+/**
+ * ViewResourceInflater is a utility class that facilitates using an Android View as a dynamic
+ * resource, which can be later used as a compositor layer. This class assumes that the View
+ * is defined declaratively, using a XML Layout file, and that the View that is going to be
+ * inflated is the single top-level View of the layout (its root).
+ *
+ * By default, the View is inflated without being attached to the hierarchy, which allows
+ * subclasses to read/modify the View "offscreen", via the method {@link #onFinishInflate()}.
+ * Only when a new snapshot of the View is required, which happens when the method
+ * {@link #invalidate()} is called, and the View is automatically detached from the
+ * hierarchy after the snapshot is captured.
+ *
+ * There's also an option to not attach to the hierarchy at all, by overriding the method
+ * {@link #shouldAttachView()} and making it return false (the default is yes). In this case
+ * the changes to the View will always be "offscreen". By default, an unspecified value of
+ * {@link View.MeasureSpec} will de used to determine the width and height of the View.
+ * It's possible to specify custom size constraints by overriding the methods
+ * {@link #getWidthMeasureSpec()} and {@link #getHeightMeasureSpec()}.
+ */
+public class ViewResourceInflater {
+
+    /**
+     * The id of the XML Layout that describes the View.
+     */
+    private int mLayoutId;
+
+    /**
+     * The id of the View being inflated, which must be the root of the given Layout.
+     */
+    private int mViewId;
+
+    /**
+     * The Context used to inflate the View.
+     */
+    private Context mContext;
+
+    /**
+     * The ViewGroup container used to inflate the View.
+     */
+    private ViewGroup mContainer;
+
+    /**
+     * The DynamicResourceLoader used to manage resources generated dynamically.
+     */
+    private DynamicResourceLoader mResourceLoader;
+
+    /**
+     * The ViewResourceAdapter used to capture snapshots of the View.
+     */
+    private ViewResourceAdapter mResourceAdapter;
+
+    /**
+     * The inflated View.
+     */
+    private View mView;
+
+    /**
+     * Whether the View is invalided.
+     */
+    private boolean mIsInvalidated;
+
+    /**
+     * Whether the View is attached to the hierarchy.
+     */
+    private boolean mIsAttached;
+
+    /**
+     * The ViewInflaterOnDrawListener used to track changes in the View when attached.
+     */
+    private ViewInflaterOnDrawListener mOnDrawListener;
+
+    /**
+     * The invalid ID.
+     */
+    private static final int INVALID_ID = -1;
+
+    /**
+     * @param layoutId          The XML Layout that declares the View.
+     * @param viewId            The id of the root View of the Layout.
+     * @param context           The Android Context used to inflate the View.
+     * @param container         The container View used to inflate the View.
+     * @param resourceLoader    The resource loader that will handle the snapshot capturing.
+     */
+    public ViewResourceInflater(int layoutId,
+                                int viewId,
+                                Context context,
+                                ViewGroup container,
+                                DynamicResourceLoader resourceLoader) {
+        mLayoutId = layoutId;
+        mViewId = viewId;
+        mContext = context;
+        mContainer = container;
+        mResourceLoader = resourceLoader;
+    }
+
+    /**
+     * Inflate the layout.
+     */
+    public void inflate() {
+        if (mView != null) return;
+
+        // Inflate the View without attaching to hierarchy (attachToRoot param is false).
+        mView = LayoutInflater.from(mContext).inflate(mLayoutId, mContainer, false);
+
+        // Make sure the View we just inflated is the right one.
+        assert mView.getId() == mViewId;
+
+        // Allow subclasses to access/modify the View before it's attached
+        // to the hierarchy (if allowed) or snapshots are captured.
+        onFinishInflate();
+
+        registerResource();
+    }
+
+    /**
+     * Invalidate the inflated View, causing a snapshot of the View to be captured.
+     */
+    public void invalidate() {
+        // View must be inflated at this point. If it's not, do it now.
+        if (mView == null) {
+            inflate();
+        }
+
+        mIsInvalidated = true;
+
+        // If the View is already attached, we don't need to do anything because the
+        // snapshot will be captured automatically when the View is drawn.
+        if (!mIsAttached) {
+            if (shouldAttachView()) {
+                // TODO(pedrosimonetti): investigate if complex views can be rendered offline.
+                // NOTE(pedrosimonetti): it seems that complex views don't get rendered
+                // properly if not attached to the hierarchy. The problem seem to be related
+                // to the use of the property "layout_gravity: end", possibly in combination
+                // of other things like elastic views (layout_weight: 1) and/or fading edges.
+                attachView();
+            } else {
+                // When the View is not attached, we need to manually layout the View
+                // and invalidate the resource in order to capture a new snapshot.
+                layout();
+                invalidateResource();
+            }
+        }
+    }
+
+    /**
+     * Destroy the instance.
+     */
+    public void destroy() {
+        if (mView == null) return;
+
+        unregisterResource();
+
+        detachView();
+        mView = null;
+
+        mLayoutId = INVALID_ID;
+        mViewId = INVALID_ID;
+
+        mContext = null;
+        mContainer = null;
+        mResourceLoader = null;
+    }
+
+    /**
+     * @return The measured width of the inflated View.
+     */
+    public int getMeasuredWidth() {
+        // View must be inflated at this point.
+        assert mView != null;
+
+        return mView.getMeasuredWidth();
+    }
+
+    /**
+     * @return The measured height of the inflated View.
+     */
+    public int getMeasuredHeight() {
+        // View must be inflated at this point.
+        assert mView != null;
+
+        return mView.getMeasuredHeight();
+    }
+
+    /**
+     * @return The id of View, which is used as an identifier for the resource loader.
+     */
+    public int getViewId() {
+        return mViewId;
+    }
+
+    /**
+     * The callback called after inflating the View, allowing subclasses to access/modify
+     * the View before it's attached to the hierarchy (if allowed) or snapshots are captured.
+     */
+    protected void onFinishInflate() {}
+
+    /**
+     * NOTE(pedrosimonetti): Complex views don't fully work when not attached to the hierarchy.
+     * @return Whether the View should be attached to the hierarchy after being inflated.
+     *         Subclasses should override this method to change the default behavior.
+     */
+    protected boolean shouldAttachView() {
+        return true;
+    }
+
+    /**
+     * @return Whether the View should be detached from the hierarchy after being captured.
+     *         Subclasses should override this method to change the default behavior.
+     */
+    protected boolean shouldDetachViewAfterCapturing() {
+        return true;
+    }
+
+    /**
+     * @return The MeasureSpec used for calculating the width of the offscreen View.
+     *         Subclasses should override this method to specify measurements.
+     *         By default, this method returns an unspecified MeasureSpec.
+     */
+    protected int getWidthMeasureSpec() {
+        return getUnspecifiedMeasureSpec();
+    }
+
+    /**
+     * @return The MeasureSpec used for calculating the height of the offscreen View.
+     *         Subclasses should override this method to specify measurements.
+     *         By default, this method returns an unspecified MeasureSpec.
+     */
+    protected int getHeightMeasureSpec() {
+        return getUnspecifiedMeasureSpec();
+    }
+
+    /**
+     * @return The View resource.
+     */
+    protected View getView() {
+        return mView;
+    }
+
+    /**
+     * Attach the View to the hierarchy.
+     */
+    private void attachView() {
+        if (!mIsAttached) {
+            assert mView.getParent() == null;
+            mContainer.addView(mView);
+            mIsAttached = true;
+
+            if (mOnDrawListener == null) {
+                // Add a draw listener. For now on, changes in the View will cause a
+                // new snapshot to be captured, if the ViewResourceInflater was invalidated.
+                mOnDrawListener = new ViewInflaterOnDrawListener();
+                mView.getViewTreeObserver().addOnDrawListener(mOnDrawListener);
+            }
+        }
+    }
+
+    /**
+     * Detach the View from the hierarchy.
+     */
+    private void detachView() {
+        if (mIsAttached) {
+            if (mOnDrawListener != null) {
+                mView.getViewTreeObserver().removeOnDrawListener(mOnDrawListener);
+                mOnDrawListener = null;
+            }
+
+            assert mView.getParent() != null;
+            mContainer.removeView(mView);
+            mIsAttached = false;
+        }
+    }
+
+    /**
+     * Layout the View. This is to be used when the View is not attached to the hierarchy.
+     */
+    private void layout() {
+        // View must be inflated at this point.
+        assert mView != null;
+
+        mView.measure(getWidthMeasureSpec(), getHeightMeasureSpec());
+        mView.layout(0, 0, getMeasuredWidth(), getMeasuredHeight());
+    }
+
+    /**
+     * @return An unspecified MeasureSpec value.
+     */
+    private int getUnspecifiedMeasureSpec() {
+        return View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
+    }
+
+    /**
+     * Register the resource and creates an adapter for it.
+     */
+    private void registerResource() {
+        if (mResourceAdapter == null) {
+            mResourceAdapter = new ViewInflaterAdapter(mView.findViewById(mViewId));
+        }
+
+        if (mResourceLoader != null) {
+            mResourceLoader.registerResource(mViewId, mResourceAdapter);
+        }
+    }
+
+    /**
+     * Unregister the resource and destroys the adapter.
+     */
+    private void unregisterResource() {
+        if (mResourceLoader != null) {
+            mResourceLoader.unregisterResource(mViewId);
+        }
+
+        mResourceAdapter = null;
+    }
+
+    /**
+     * Invalidate the resource, which will cause a new snapshot to be captured.
+     */
+    private void invalidateResource() {
+        if (mIsInvalidated && mView != null && mResourceAdapter != null) {
+            mIsInvalidated = false;
+            mResourceAdapter.invalidate(null);
+        }
+    }
+
+    /**
+     * A custom {@link ViewResourceAdapter} that calls the method {@link #onCaptureEnd()}.
+     */
+    private class ViewInflaterAdapter extends ViewResourceAdapter {
+        public ViewInflaterAdapter(View view) {
+            super(view);
+        }
+
+        @Override
+        protected void onCaptureEnd() {
+            ViewResourceInflater.this.onCaptureEnd();
+        }
+    }
+
+    /**
+     * Called when a snapshot is captured.
+     */
+    private void onCaptureEnd() {
+        if (shouldDetachViewAfterCapturing()) {
+            detachView();
+        }
+    }
+
+    /**
+     * A custom {@link ViewTreeObserver.OnDrawListener} that calls the method {@link #onDraw()}.
+     */
+    private class ViewInflaterOnDrawListener implements ViewTreeObserver.OnDrawListener {
+        @Override
+        public void onDraw() {
+            ViewResourceInflater.this.onDraw();
+        }
+    }
+
+    /**
+     * Called when the View is drawn,
+     */
+    private void onDraw() {
+        invalidateResource();
+    }
+}