Added compatibility WebView for API<19 with custom method for executing JS

Author: aforcier

WordPressEditor/src/main/java/org/wordpress/android/editor/EditorWebViewCompatibility.java

@@ -0,0 +1,115 @@
+package org.wordpress.android.editor;
+
+import android.content.Context;
+import android.os.Build;
+import android.os.Message;
+import android.util.AttributeSet;
+import android.webkit.WebView;
+
+import org.wordpress.android.util.AppLog;
+import org.wordpress.android.util.AppLog.T;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+/**
+ * <p>Compatibility <code>EditorWebView</code> for pre-Chromium WebView (API<19). Provides a custom method for executing
+ * JavaScript, {@link #loadJavaScript(String)}, instead of {@link WebView#loadUrl(String)}. This is needed because
+ * <code>WebView#loadUrl(String)</code> on API<19 eventually calls <code>WebViewClassic#hideSoftKeyboard()</code>,
+ * hiding the keyboard whenever JavaScript is executed.</p>
+ *
+ * <p>This class uses reflection to access the normally inaccessible <code>WebViewCore#sendMessage(Message)</code>
+ * and use it to execute JavaScript, sidestepping <code>WebView#loadUrl(String)</code> and the keyboard issue.</p>
+ */
+@SuppressWarnings("TryWithIdenticalCatches")
+public class EditorWebViewCompatibility extends EditorWebViewAbstract {
+    private static final int EXECUTE_JS = 194; // WebViewCore internal JS message code
+
+    private Object mWebViewCore;
+    private Method mSendMessageMethod;
+
+    public EditorWebViewCompatibility(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        try {
+            this.initReflection();
+        } catch (ReflectionException e) {
+            AppLog.e(T.EDITOR, e);
+            handleReflectionFailure();
+        }
+    }
+
+    private void initReflection() throws ReflectionException {
+        Object webViewProvider;
+
+        try {
+            if (Build.VERSION.SDK_INT >= 16) {
+                // On API >= 16, the WebViewCore instance is not defined inside WebView itself but inside a
+                // WebViewClassic (implementation of WebViewProvider), referenced from the WebView as mProvider
+
+                // Access WebViewClassic object
+                Field webViewProviderField = WebView.class.getDeclaredField("mProvider");
+                webViewProviderField.setAccessible(true);
+                webViewProvider = webViewProviderField.get(this);
+
+                // Access WebViewCore object
+                Field webViewCoreField = webViewProvider.getClass().getDeclaredField("mWebViewCore");
+                webViewCoreField.setAccessible(true);
+                mWebViewCore = webViewCoreField.get(webViewProvider);
+            } else {
+                // On API < 16, the WebViewCore is directly accessible from the WebView
+
+                // Access WebViewCore object
+                Field webViewCoreField = WebView.class.getDeclaredField("mWebViewCore");
+                webViewCoreField.setAccessible(true);
+                mWebViewCore = webViewCoreField.get(this);
+            }
+
+            // Access WebViewCore#sendMessage(Message) method
+            if (mWebViewCore != null) {
+                mSendMessageMethod = mWebViewCore.getClass().getDeclaredMethod("sendMessage", Message.class);
+                mSendMessageMethod.setAccessible(true);
+            }
+        } catch (NoSuchFieldException e) {
+            throw new ReflectionException(e);
+        } catch (NoSuchMethodException e) {
+            throw new ReflectionException(e);
+        } catch (IllegalAccessException e) {
+            throw new ReflectionException(e);
+        }
+    }
+
+    private void loadJavaScript(final String javaScript) throws ReflectionException {
+        if (mSendMessageMethod == null) {
+            initReflection();
+        } else {
+            Message jsMessage = Message.obtain(null, EXECUTE_JS, javaScript);
+            try {
+                mSendMessageMethod.invoke(mWebViewCore, jsMessage);
+            } catch (InvocationTargetException e) {
+                throw new ReflectionException(e);
+            } catch (IllegalAccessException e) {
+                throw new ReflectionException(e);
+            }
+        }
+    }
+
+    public void execJavaScriptFromString(String javaScript) {
+        try {
+            loadJavaScript(javaScript);
+        } catch(ReflectionException e) {
+            AppLog.e(T.EDITOR, e);
+            handleReflectionFailure();
+        }
+    }
+
+    private void handleReflectionFailure() {
+        // TODO: Fallback to legacy editor and pass the error to analytics
+    }
+
+    public class ReflectionException extends Exception {
+        public ReflectionException(Throwable cause) {
+            super(cause);
+        }
+    }
+}