Qt: Set IO Graph display filter when having Y field

Calling setFilter() between setValueUnits() and setValueUnitField()
will fail when having "Y Field" because check_field_unit() fails
with inconsistent values.  The display filter will then be ignored.

Call setFilter() first to ensure filter_ is set before setting
value units.  setFilter() does not depend on the value unit when
used to set the display filter.

Change-Id: Ibf2d37fddcce9fcf6febebfefa0b2518ae093737
Fixes: v2.3.0rc0-2930-g0ea51ad822 ("Qt: Fix uninitialized memory access in val_units_")
Reviewed-on: https://code.wireshark.org/review/22619
Petri-Dish: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Stig Bjørlykke <stig@bjorlykke.org>

1 files changed, 12 insertions, 4 deletions

diff --git a/ui/qt/io_graph_dialog.cpp b/ui/qt/io_graph_dialog.cpp
index c7960db4b8..2024d76684 100644
--- a/ui/qt/io_graph_dialog.cpp
+++ b/ui/qt/io_graph_dialog.cpp
@@ -404,6 +404,15 @@ void IOGraphDialog::addDefaultGraph(bool enabled, int idx)
 
 // Sync the settings from a graphTreeWidget item to its IOGraph.
 // Disables the graph if any errors are found.
+//
+// NOTE: Setting dfilter, yaxis and yfield here will all end up in setFilter() and this
+//       has a chicken-and-egg problem because setFilter() depends on previous assigned
+//       values for filter_, val_units_ and vu_field_.  Setting values in wrong order
+//       may give unpredicted results because setFilter() does not always set filter_
+//       on errors.
+// TODO: The issues in the above note should be fixed and setFilter() should not be
+//       called so frequently.
+
 void IOGraphDialog::syncGraphSettings(QTreeWidgetItem *item)
 {
     if (!item) return;
@@ -414,16 +423,15 @@ void IOGraphDialog::syncGraphSettings(QTreeWidgetItem *item)
     bool retap = !iog->visible() && visible;
 
     iog->setName(item->text(name_col_));
+    iog->setFilter(item->text(dfilter_col_));
 
-    /* dfilter and plot style depend on the value unit, so set it first. */
+    /* plot style depend on the value unit, so set it first. */
     iog->setValueUnits(item->data(yaxis_col_, Qt::UserRole).toInt());
+    iog->setValueUnitField(item->text(yfield_col_));
 
-    iog->setFilter(item->text(dfilter_col_));
     iog->setColor(colors_[item->data(color_col_, Qt::UserRole).toInt() % colors_.size()]);
     iog->setPlotStyle(item->data(style_col_, Qt::UserRole).toInt());
 
-    iog->setValueUnitField(item->text(yfield_col_));
-
     iog->moving_avg_period_ = item->data(sma_period_col_, Qt::UserRole).toUInt();
 
     iog->setInterval(ui->intervalComboBox->itemData(ui->intervalComboBox->currentIndex()).toInt());