[TD]use weak_ptr as deletion guard

- prevent crash if dimension deleted by Python while dialog
  is open

src/Mod/TechDraw/Gui/TaskDimension.cpp

@@ -47,11 +47,10 @@ using namespace TechDraw;
 using namespace TechDrawGui;
 
 TaskDimension::TaskDimension(QGIViewDimension *parent, ViewProviderDimension *dimensionVP) :
-    ui(new Ui_TaskDimension)
+    ui(new Ui_TaskDimension),
+    m_parent(parent),
+    m_dimensionVP(dimensionVP)
 {
-    m_parent = parent;
-    m_dimensionVP = dimensionVP;
-
     ui->setupUi(this);
 
     // Tolerancing
@@ -143,6 +142,11 @@ TaskDimension::~TaskDimension()
 
 bool TaskDimension::accept()
 {
+    if (m_dimensionVP.expired()) {
+        QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Missing Dimension"),
+                                               QObject::tr("Dimension not found.  Was it deleted? Can not continue."));
+        return true;
+    }
     Gui::Document* doc = m_dimensionVP->getDocument();
     m_dimensionVP->getObject()->purgeTouched();
     doc->commitCommand();
@@ -153,6 +157,11 @@ bool TaskDimension::accept()
 
 bool TaskDimension::reject()
 {
+    if (m_dimensionVP.expired()) {
+        QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Missing Dimension"),
+                                               QObject::tr("Dimension not found.  Was it deleted? Can not continue."));
+        return true;
+    }
     Gui::Document* doc = m_dimensionVP->getDocument();
     doc->abortCommand();
     recomputeFeature();
@@ -165,6 +174,10 @@ bool TaskDimension::reject()
 
 void TaskDimension::recomputeFeature()
 {
+    if (m_dimensionVP.expired()) {
+        // guard against deletion while this dialog is running
+        return;
+    }
     App::DocumentObject* objVP = m_dimensionVP->getObject();
     assert(objVP);
     objVP->getDocument()->recomputeFeature(objVP);
@@ -297,12 +310,18 @@ void TaskDimension::onArbitraryTolerancesChanged()
 
 void TaskDimension::onFlipArrowheadsChanged()
 {
+    if (m_dimensionVP.expired()) {
+        return;
+    }
     m_dimensionVP->FlipArrowheads.setValue(ui->cbArrowheads->isChecked());
     recomputeFeature();
 }
 
 void TaskDimension::onColorChanged()
 {
+    if (m_dimensionVP.expired()) {
+        return;
+    }
     App::Color ac;
     ac.setValue<QColor>(ui->dimensionColor->color());
     m_dimensionVP->Color.setValue(ac);
@@ -311,12 +330,18 @@ void TaskDimension::onColorChanged()
 
 void TaskDimension::onFontsizeChanged()
 {
+    if (m_dimensionVP.expired()) {
+        return;
+    }
     m_dimensionVP->Fontsize.setValue(ui->qsbFontSize->value().getValue());
     recomputeFeature();
 }
 
 void TaskDimension::onDrawingStyleChanged()
 {
+    if (m_dimensionVP.expired()) {
+        return;
+    }
     m_dimensionVP->StandardAndStyle.setValue(ui->comboDrawingStyle->currentIndex());
     recomputeFeature();
 }

src/Mod/TechDraw/Gui/TaskDimension.h

@@ -23,6 +23,7 @@
 #ifndef GUI_TASKVIEW_TASKDIMENSION_H
 #define GUI_TASKVIEW_TASKDIMENSION_H
 
+#include <Gui/DocumentObserver.h>
 #include <Gui/TaskView/TaskDialog.h>
 #include <Gui/TaskView/TaskView.h>
 #include <Mod/TechDraw/TechDrawGlobal.h>
@@ -72,7 +73,7 @@ private Q_SLOTS:
 private:
     std::unique_ptr<Ui_TaskDimension> ui;
     QGIViewDimension *m_parent;
-    ViewProviderDimension *m_dimensionVP;
+    Gui::WeakPtrT<ViewProviderDimension> m_dimensionVP;
     std::pair<double, bool> getAngleFromSelection();
 };