Improve data form API

Add

DataForm.getField(String)
DataForm.getHiddenFormTypeField()

smack-extensions/src/main/java/org/jivesoftware/smackx/xdata/FormField.java

@@ -35,6 +35,11 @@ public class FormField {
 
     public static final String ELEMENT = "field";
 
+    /**
+     * The constant String "FORM_TYPE"
+     */
+    public static final String FORM_TYPE = "FORM_TYPE";
+
     /**
      * Form Field Types as defined in XEP-4 § 3.3.
      * 
@@ -118,10 +123,11 @@ public class FormField {
         }
     }
 
+    private final String variable;
+
     private String description;
     private boolean required = false;
     private String label;
-    private String variable;
     private Type type;
     private final List<Option> options = new ArrayList<Option>();
     private final List<String> values = new ArrayList<String>();
@@ -142,6 +148,7 @@ public class FormField {
      * name.
      */
     public FormField() {
+        this(null);
         this.type = Type.fixed;
     }
 
@@ -214,7 +221,12 @@ public class FormField {
 
     /**
      * Returns the variable name that the question is filling out.
-     *
+     * <p>
+     * According to XEP-4 § 3.2 the variable name (the 'var' attribute)
+     * "uniquely identifies the field in the context of the form" (if the field is not of type 'fixed', in which case
+     * the field "MAY possess a 'var' attribute")
+     * </p>
+     * 
      * @return the variable name of the question.
      */
     public String getVariable() {
@@ -270,11 +282,19 @@ public class FormField {
 
     /**
      * Sets an indicative of the format for the data to answer.
+     * <p>
+     * This method will throw an IllegalArgumentException if type is 'fixed'. To create FormFields of type 'fixed' use
+     * {@link #FormField()} instead.
+     * </p>
      *
      * @param type an indicative of the format for the data to answer.
      * @see Type
+     * @throws IllegalArgumentException if type is 'fixed'.
      */
     public void setType(Type type) {
+        if (type == Type.fixed) {
+            throw new IllegalArgumentException("Can not set type to fixed, use FormField constructor without arguments instead.");
+        }
         this.type = type;
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/xdata/packet/DataForm.java

@@ -125,6 +125,24 @@ public class DataForm implements PacketExtension {
         }
     }
 
+    /**
+     * Return the form field with the given variable name or null.
+     *
+     * @param variableName
+     * @return the form field or null.
+     * @since 4.1
+     */
+    public FormField getField(String variableName) {
+        synchronized (fields) {
+            for (FormField field : fields) {
+                if (variableName.equals(field.getVariable())) {
+                    return field;
+                }
+            }
+        }
+        return null;
+    }
+
     public String getElementName() {
         return ELEMENT;
     }
@@ -169,6 +187,11 @@ public class DataForm implements PacketExtension {
      * @param field the field to add to the form.
      */
     public void addField(FormField field) {
+        String fieldVariableName = field.getVariable();
+        if (fieldVariableName != null && getField(fieldVariableName) != null) {
+            throw new IllegalArgumentException("This data form already contains a form field with the variable name '"
+                            + fieldVariableName + "'");
+        }
         synchronized (fields) {
             fields.add(field);
         }
@@ -206,6 +229,20 @@ public class DataForm implements PacketExtension {
         return Collections.unmodifiableList(extensionElements);
     }
 
+    /**
+     * Returns the hidden FORM_TYPE field or null if this data form has none.
+     *
+     * @return the hidden FORM_TYPE field or null.
+     * @since 4.1
+     */
+    public FormField getHiddenFormTypeField() {
+        FormField field = getField(FormField.FORM_TYPE);
+        if (field != null && field.getType() == FormField.Type.hidden) {
+            return field;
+        }
+        return null;
+    }
+
     /**
      * Returns true if this DataForm has at least one FORM_TYPE field which is
      * hidden. This method is used for sanity checks.
@@ -213,12 +250,7 @@ public class DataForm implements PacketExtension {
      * @return true if there is at least one field which is hidden.
      */
     public boolean hasHiddenFormTypeField() {
-        for (FormField f : fields) {
-            if (f.getVariable().equals("FORM_TYPE") && f.getType() == FormField.Type.hidden) {
-                return true;
-            }
-        }
-        return false;
+        return getHiddenFormTypeField() != null;
     }
 
     @Override