1.1 --- a/src/de/matthiasmann/twl/model/AbstractProperty.java	Mon Jan 09 23:15:31 2012 +0100
     1.2 +++ b/src/de/matthiasmann/twl/model/AbstractProperty.java	Thu Jan 12 08:29:00 2012 +0100
     1.3 @@ -1,5 +1,5 @@
     1.4  /*
     1.5 - * Copyright (c) 2008-2009, Matthias Mann
     1.6 + * Copyright (c) 2008-2012, Matthias Mann
     1.7   *
     1.8   * All rights reserved.
     1.9   *
    1.10 @@ -39,7 +39,7 @@
    1.11   */
    1.12  public abstract class AbstractProperty<T> implements Property<T> {
    1.13  
    1.14 -    private Runnable[] valueChangedCallbacks = null;
    1.15 +    private Runnable[] valueChangedCallbacks;
    1.16  
    1.17      public void addValueChangedCallback(Runnable cb) {
    1.18          valueChangedCallbacks = CallbackSupport.addCallbackToList(
    1.19 @@ -51,6 +51,10 @@
    1.20                  valueChangedCallbacks, cb);
    1.21      }
    1.22  
    1.23 +    public boolean hasValueChangedCallbacks() {
    1.24 +        return valueChangedCallbacks != null;
    1.25 +    }
    1.26 +    
    1.27      protected void fireValueChangedCallback() {
    1.28          CallbackSupport.fireCallbacks(valueChangedCallbacks);
    1.29      }

     2.1 --- a/src/de/matthiasmann/twl/model/HasCallback.java	Mon Jan 09 23:15:31 2012 +0100
     2.2 +++ b/src/de/matthiasmann/twl/model/HasCallback.java	Thu Jan 12 08:29:00 2012 +0100
     2.3 @@ -1,5 +1,5 @@
     2.4  /*
     2.5 - * Copyright (c) 2008-2011, Matthias Mann
     2.6 + * Copyright (c) 2008-2012, Matthias Mann
     2.7   *
     2.8   * All rights reserved.
     2.9   *
    2.10 @@ -61,6 +61,14 @@
    2.11      }
    2.12  
    2.13      /**
    2.14 +     * Returns true when the callback list is not empty
    2.15 +     * @return true when the callback list is not empty
    2.16 +     */
    2.17 +    public boolean hasCallbacks() {
    2.18 +        return callbacks != null;
    2.19 +    }
    2.20 +    
    2.21 +    /**
    2.22       * Calls all registered callbacks.
    2.23       *
    2.24       * Callbacks can call {@code addCallback} or {@code removeCallback}.