Check for null/emtpy values in dialog box

Before we let the user start the execution we will check for null
values every time that the attributes change. This is true for
both the clustering attribute and the threshold attribute.

- At the moment the dialog will display a dialog box, but this
could change to a message in the message bar.

Author: sergiobuj

clusterpy_lightdialog.py

@@ -39,7 +39,6 @@ def __init__(self):
         self.help_browser.setHtml(abouthtml)
 
 class maxpDialog(QtGui.QDialog, Ui_maxp_ui):
-    DONE_MSG = "Finish"
 
     def __init__(self):
         QtGui.QDialog.__init__(self)
@@ -48,6 +47,10 @@ def __init__(self):
                         QtCore.SIGNAL("currentIndexChanged(int)"),
                         self.updateThresholdLimits)
 
+        self.connect(self.attribute_combo,
+                QtCore.SIGNAL("currentIndexChanged(int)"),
+                self.checkAttrValues)
+
         self.connect(self.layer_combo,
                         QtCore.SIGNAL("currentIndexChanged(int)"),
                         self.updateAttrCombo)
@@ -77,18 +80,46 @@ def updateAttrCombo(self, newindex):
             self.attribute_combo.addItems(fieldNames)
             self.threshold_attr_combo.addItems(fieldNames2)
 
+    def checkAttrValues(self, newindex):
+        if newindex > -1:
+            attributeName = self.attribute_combo.currentText()
+            self.checkAllValues(attributeName)
+
+    def checkAllValues(self, attributeName):
+        layerIndex = self.layer_combo.currentIndex()
+        fiterator = self.mc.layer(layerIndex).dataProvider().getFeatures()
+
+        valid = True
+        maximum = 0
+        minimum = 99999
+        for feature in fiterator:
+            val = feature.attribute(attributeName)
+            try:
+                minimum = val if val < minimum else minimum
+                maximum += val
+            except TypeError:
+                valid = False
+
+        if not valid:
+            null_message  = "Some values are missing.\n" +\
+            "Check the Attribute Table for NULL or empty values.\n" +\
+            "Column: " + str(attributeName) + "\n" +\
+            "Please update the Attribute Table in order to run Max-p."
+
+            # Showing a message box might be better to get the user's attention
+            QtGui.QMessageBox.warning(self, "Clusterpy", null_message)
+            #self.showMessage("Clusterpy Error", "NULL or Empty Attrs",
+            #    level=QgsMessageBar.CRITICAL)
+
+        return minimum, maximum
+
     def updateThresholdLimits(self, newindex):
         if newindex > -1:
             layerIndex = self.layer_combo.currentIndex()
             fiterator = self.mc.layer(layerIndex).dataProvider().getFeatures()
             attributeName = self.threshold_attr_combo.currentText()
 
-            maximum = 0
-            minimum = 99999
-            for feature in fiterator:
-                val = feature.attribute(attributeName)
-                minimum = val if val < minimum else minimum
-                maximum += val
+            minimum, maximum = self.checkAllValues(attributeName)
 
             self.threshold_spin.setMinimum(minimum)
             self.threshold_spin.setMaximum(maximum)
@@ -145,8 +176,8 @@ def finishRun(self, success, outputmsg):
         self.okbutton.setEnabled(True)
         if success:
             self.addToCanvas()
-            output_msg = "Success. New column added to attribute table. " + outputmsg
-            self.showMessage("Clusterpy", output_msg, duration=0 )
+            msg = "Success. New column added to attribute table. " + outputmsg
+            self.showMessage("Clusterpy", msg, duration=0 )
         else:
             self.showMessage("Clusterpy Error",
                                         outputmsg,