change fromDialog() to return a Maybe instead of an Observable

Author: thomasnield

src/main/java/io/reactivex/rxjavafx/observables/JavaFxObservable.java

@@ -16,6 +16,7 @@
 package io.reactivex.rxjavafx.observables;
 
 
+import io.reactivex.Maybe;
 import io.reactivex.Observable;
 import io.reactivex.rxjavafx.sources.*;
 import javafx.beans.value.ObservableValue;
@@ -367,9 +368,9 @@ public static Observable<Long> interval(final Duration duration) {
     }
 
     /**
-     * Returns an Observable that emits the T response  of a Dialog. If no response was given then the Observable will be empty.
+     * Returns a Maybe that emits the T response  of a Dialog. If no response was given then the Maybe will be empty.
      */
-    public static <T> Observable<T> fromDialog(Dialog<T> dialog) {
+    public static <T> Maybe<T> fromDialog(Dialog<T> dialog) {
         return DialogSource.fromDialogSource(dialog);
     }
 }

src/main/java/io/reactivex/rxjavafx/sources/DialogSource.java

@@ -15,16 +15,18 @@
  */
 package io.reactivex.rxjavafx.sources;
 
-import io.reactivex.Observable;
+import io.reactivex.Maybe;
+import io.reactivex.Single;
 import io.reactivex.rxjavafx.schedulers.JavaFxScheduler;
 import javafx.scene.control.Dialog;
+
 import java.util.Optional;
 
 public final class DialogSource {
     private DialogSource() {}
 
-    public static <T> Observable<T> fromDialogSource(final Dialog<T> dialog) {
-        return Observable.fromCallable(dialog::showAndWait)
+    public static <T> Maybe<T> fromDialogSource(final Dialog<T> dialog) {
+        return Single.fromCallable(dialog::showAndWait)
                 .subscribeOn(JavaFxScheduler.platform())
                 .filter(Optional::isPresent)
                 .map(Optional::get);