fixing the result handlers and orientation changes

briar-android/src/org/briarproject/android/controller/handler/UiContextExceptionResultHandler.java

@@ -0,0 +1,68 @@
+package org.briarproject.android.controller.handler;
+
+import android.support.annotation.Nullable;
+import android.support.annotation.UiThread;
+
+import org.briarproject.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * This class defines a result handler with a callback that runs on the UI thread
+ * and is retained when orientation changes occur. It ensures that the callback
+ * is always run in the latest context.
+ * <p>
+ * Note that this event handler should be used carefully with callbacks that
+ * depend on global variables as those variables might be destroyed or lose their
+ * state during the orientation change.
+ *
+ * @param <R> The result's object type
+ */
+@Immutable
+@NotNullByDefault
+public abstract class UiContextExceptionResultHandler<R, E extends Exception>
+		extends UiContextResultHandler<R>
+		implements ResultExceptionHandler<R, E> {
+
+	@Nullable
+	private E exception;
+
+	protected UiContextExceptionResultHandler(
+			DestroyableContextManager listener, String tag) {
+		super(listener, tag);
+	}
+
+	@Override
+	public void setDestroyableContextManager(
+			DestroyableContextManager listener) {
+		boolean isSwitchingFromNullToNonNull =
+				this.listener == null && listener != null;
+		super.setDestroyableContextManager(listener);
+		if (isSwitchingFromNullToNonNull)
+			runException();
+	}
+
+	@Override
+	public void onException(final E exception) {
+		this.exception = exception;
+		listener.runOnUiThreadUnlessDestroyed(new Runnable() {
+			@Override
+			public void run() {
+				runException();
+			}
+		});
+	}
+
+	@UiThread
+	private void runException() {
+		if (exception != null && listener != null) {
+			onExceptionUi(exception, listener);
+			listener.removeContextResultHandler(getTag());
+			exception = null;
+		}
+	}
+
+	@UiThread
+	public abstract void onExceptionUi(E exception,
+			DestroyableContextManager context);
+}