[Remoting Android] Make JniClient own JniDisplayHandler

remoting/android/java/src/org/chromium/chromoting/jni/Client.java

Index: remoting/android/java/src/org/chromium/chromoting/jni/Client.java
diff --git a/remoting/android/java/src/org/chromium/chromoting/jni/Client.java b/remoting/android/java/src/org/chromium/chromoting/jni/Client.java
index 628573a0162934586f2d3f5d58396c918c06eba8..058fcac32a59ec182ff9210b3a1d1118df470ce2 100644
--- a/remoting/android/java/src/org/chromium/chromoting/jni/Client.java
+++ b/remoting/android/java/src/org/chromium/chromoting/jni/Client.java
@@ -23,9 +23,8 @@ public class Client implements InputStub {
     // Pointer to the C++ object, cast to a |long|.
     private long mNativeJniClient;
 
-    // Reference has to be kept until the lifecycle of Client ends. Code are currently using
-    // getDisplay() without doing a null check.
-    private Display mDisplay;
+    // Implementation-dependent display object used by the desktop view.
+    private Object mDisplay;
 
     // The global Client instance (may be null). This needs to be a global singleton so that the
     // Client can be passed between Activities.
@@ -41,11 +40,20 @@ public class Client implements InputStub {
     }
 
     /**
-     * Returns the display object. It will be null before calling connectToHost() but won't be null
-     *          after calling disconnectFromHost().
+     * Sets the display object. Called by the native code when the connection starts.
+     * @param display the implementation-dependent object used by the desktop view.
+     */
+    @CalledByNative
+    private void setDisplay(Object display) {

[Lambros, 2016/06/29 00:18:39]

I think you could use Display instead of Object here. Looking elsewhere in
Chromium, I see examples of methods that are @CalledByNative, but they still
specify the proper type of their parameters.
For example:
https://cs.chromium.org/chromium/src/base/android/jni_generator/jni_generator...
I think you'll get a ClassCastException if you try to pass the wrong type of
object from native code.

[Yuwei, 2016/06/29 00:40:09]

As discussed offline,

* The point of passing and storing Object is that different implementations of
DesktopView will expect different type of Display object.
* The Java client will no longer need to access the display object so it doesn't
(and shouldn't) need to know the type information.

+        mDisplay = display;
+    }
+
+    /**
+     * Returns the display object. It will be null before calling connectToHost() or after calling
+     * disconnectFromHost().
      * @return the display object.
      */
-    public Display getDisplay() {
+    public Object getDisplay() {

[Lambros, 2016/06/29 00:18:39]

Even if you needed the instanceof checking, you could still return Display and
put the instanceof check inside here instead of the calling code.

         return mDisplay;
     }
 
@@ -93,8 +101,7 @@ public class Client implements InputStub {
 
         mConnectionListener = listener;
         mAuthenticator = authenticator;
-        mDisplay = new Display();
-        nativeConnect(mNativeJniClient, mDisplay.getNativePointer(), username, authToken, hostJid,
+        nativeConnect(mNativeJniClient, username, authToken, hostJid,
                 hostId, hostPubkey, mAuthenticator.getPairingId(hostId),
                 mAuthenticator.getPairingSecret(hostId), mCapabilityManager.getLocalCapabilities(),
                 flags);
@@ -124,7 +131,7 @@ public class Client implements InputStub {
         mConnected = false;
         mCapabilityManager.onHostDisconnect();
 
-        mDisplay.destroy();
+        mDisplay = null;
     }
 
     /** Called whenever the connection status changes. */
@@ -296,7 +303,7 @@ public class Client implements InputStub {
     private native void nativeDestroy(long nativeJniClient);
 
     /** Performs the native portion of the connection. */
-    private native void nativeConnect(long nativeJniClient, long nativeJniDisplayHandler,
+    private native void nativeConnect(long nativeJniClient,
             String username, String authToken, String hostJid, String hostId, String hostPubkey,
             String pairId, String pairSecret, String capabilities, String flags);