Java tutorial
// Copyright (c) 2012 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.content.browser.accessibility; import android.content.Context; import android.os.Bundle; import android.os.SystemClock; import android.view.View; import android.view.accessibility.AccessibilityNodeInfo; import org.chromium.content.browser.ContentViewCore; import org.chromium.content.browser.JavascriptInterface; import org.json.JSONException; import org.json.JSONObject; import java.util.Iterator; import java.util.concurrent.atomic.AtomicInteger; /** * Handles injecting accessibility Javascript and related Javascript -> Java APIs for JB and newer * devices. */ class JellyBeanAccessibilityInjector extends AccessibilityInjector { private CallbackHandler mCallback; private JSONObject mAccessibilityJSONObject; private static final String ALIAS_TRAVERSAL_JS_INTERFACE = "accessibilityTraversal"; // Template for JavaScript that performs AndroidVox actions. private static final String ACCESSIBILITY_ANDROIDVOX_TEMPLATE = "cvox.AndroidVox.performAction('%1s')"; /** * Constructs an instance of the JellyBeanAccessibilityInjector. * @param view The ContentViewCore that this AccessibilityInjector manages. */ protected JellyBeanAccessibilityInjector(ContentViewCore view) { super(view); } @Override public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) { info.setMovementGranularities(AccessibilityNodeInfo.MOVEMENT_GRANULARITY_CHARACTER | AccessibilityNodeInfo.MOVEMENT_GRANULARITY_WORD | AccessibilityNodeInfo.MOVEMENT_GRANULARITY_LINE | AccessibilityNodeInfo.MOVEMENT_GRANULARITY_PARAGRAPH | AccessibilityNodeInfo.MOVEMENT_GRANULARITY_PAGE); info.addAction(AccessibilityNodeInfo.ACTION_NEXT_AT_MOVEMENT_GRANULARITY); info.addAction(AccessibilityNodeInfo.ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY); info.addAction(AccessibilityNodeInfo.ACTION_NEXT_HTML_ELEMENT); info.addAction(AccessibilityNodeInfo.ACTION_PREVIOUS_HTML_ELEMENT); info.addAction(AccessibilityNodeInfo.ACTION_CLICK); info.setClickable(true); } @Override public boolean supportsAccessibilityAction(int action) { if (action == AccessibilityNodeInfo.ACTION_NEXT_AT_MOVEMENT_GRANULARITY || action == AccessibilityNodeInfo.ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY || action == AccessibilityNodeInfo.ACTION_NEXT_HTML_ELEMENT || action == AccessibilityNodeInfo.ACTION_PREVIOUS_HTML_ELEMENT || action == AccessibilityNodeInfo.ACTION_CLICK) { return true; } return false; } @Override public boolean performAccessibilityAction(int action, Bundle arguments) { if (!accessibilityIsAvailable() || !mContentViewCore.isAlive() || !mInjectedScriptEnabled || !mScriptInjected) { return false; } boolean actionSuccessful = sendActionToAndroidVox(action, arguments); if (actionSuccessful) mContentViewCore.showImeIfNeeded(); return actionSuccessful; } @Override protected void addAccessibilityApis() { super.addAccessibilityApis(); Context context = mContentViewCore.getContext(); if (context != null && mCallback == null) { mCallback = new CallbackHandler(ALIAS_TRAVERSAL_JS_INTERFACE); mContentViewCore.addJavascriptInterface(mCallback, ALIAS_TRAVERSAL_JS_INTERFACE); } } @Override protected void removeAccessibilityApis() { super.removeAccessibilityApis(); if (mCallback != null) { mContentViewCore.removeJavascriptInterface(ALIAS_TRAVERSAL_JS_INTERFACE); mCallback = null; } } /** * Packs an accessibility action into a JSON object and sends it to AndroidVox. * * @param action The action identifier. * @param arguments The action arguments, if applicable. * @return The result of the action. */ private boolean sendActionToAndroidVox(int action, Bundle arguments) { if (mCallback == null) return false; if (mAccessibilityJSONObject == null) { mAccessibilityJSONObject = new JSONObject(); } else { // Remove all keys from the object. final Iterator<?> keys = mAccessibilityJSONObject.keys(); while (keys.hasNext()) { keys.next(); keys.remove(); } } try { mAccessibilityJSONObject.accumulate("action", action); if (arguments != null) { if (action == AccessibilityNodeInfo.ACTION_NEXT_AT_MOVEMENT_GRANULARITY || action == AccessibilityNodeInfo.ACTION_PREVIOUS_AT_MOVEMENT_GRANULARITY) { final int granularity = arguments .getInt(AccessibilityNodeInfo.ACTION_ARGUMENT_MOVEMENT_GRANULARITY_INT); mAccessibilityJSONObject.accumulate("granularity", granularity); } else if (action == AccessibilityNodeInfo.ACTION_NEXT_HTML_ELEMENT || action == AccessibilityNodeInfo.ACTION_PREVIOUS_HTML_ELEMENT) { final String element = arguments .getString(AccessibilityNodeInfo.ACTION_ARGUMENT_HTML_ELEMENT_STRING); mAccessibilityJSONObject.accumulate("element", element); } } } catch (JSONException ex) { return false; } final String jsonString = mAccessibilityJSONObject.toString(); final String jsCode = String.format(ACCESSIBILITY_ANDROIDVOX_TEMPLATE, jsonString); return mCallback.performAction(mContentViewCore, jsCode); } private static class CallbackHandler { private static final String JAVASCRIPT_ACTION_TEMPLATE = "(function() {" + " retVal = false;" + " try {" + " retVal = %s;" + " } catch (e) {" + " retVal = false;" + " }" + " %s.onResult(%d, retVal);" + "})()"; // Time in milliseconds to wait for a result before failing. private static final long RESULT_TIMEOUT = 5000; private final AtomicInteger mResultIdCounter = new AtomicInteger(); private final Object mResultLock = new Object(); private final String mInterfaceName; private boolean mResult = false; private long mResultId = -1; private CallbackHandler(String interfaceName) { mInterfaceName = interfaceName; } /** * Performs an action and attempts to wait for a result. * * @param contentView The ContentViewCore to perform the action on. * @param code Javascript code that evaluates to a result. * @return The result of the action. */ private boolean performAction(ContentViewCore contentView, String code) { final int resultId = mResultIdCounter.getAndIncrement(); final String js = String.format(JAVASCRIPT_ACTION_TEMPLATE, code, mInterfaceName, resultId); contentView.evaluateJavaScript(js, null); return getResultAndClear(resultId); } /** * Gets the result of a request to perform an accessibility action. * * @param resultId The result id to match the result with the request. * @return The result of the request. */ private boolean getResultAndClear(int resultId) { synchronized (mResultLock) { final boolean success = waitForResultTimedLocked(resultId); final boolean result = success ? mResult : false; clearResultLocked(); return result; } } /** * Clears the result state. */ private void clearResultLocked() { mResultId = -1; mResult = false; } /** * Waits up to a given bound for a result of a request and returns it. * * @param resultId The result id to match the result with the request. * @return Whether the result was received. */ private boolean waitForResultTimedLocked(int resultId) { long waitTimeMillis = RESULT_TIMEOUT; final long startTimeMillis = SystemClock.uptimeMillis(); while (true) { try { if (mResultId == resultId) return true; if (mResultId > resultId) return false; final long elapsedTimeMillis = SystemClock.uptimeMillis() - startTimeMillis; waitTimeMillis = RESULT_TIMEOUT - elapsedTimeMillis; if (waitTimeMillis <= 0) return false; mResultLock.wait(waitTimeMillis); } catch (InterruptedException ie) { /* ignore */ } } } /** * Callback exposed to JavaScript. Handles returning the result of a * request to a waiting (or potentially timed out) thread. * * @param id The result id of the request as a {@link String}. * @param result The result of a request as a {@link String}. */ @JavascriptInterface @SuppressWarnings("unused") public void onResult(String id, String result) { final long resultId; try { resultId = Long.parseLong(id); } catch (NumberFormatException e) { return; } synchronized (mResultLock) { if (resultId > mResultId) { mResult = Boolean.parseBoolean(result); mResultId = resultId; } mResultLock.notifyAll(); } } } }