Delay applying a changed filter value

When changing a filter value delay the application of the new value on
the table for a couple of milliseconds. This makes the filter process
much smoother for fast typing users working on large tables.

See issue #415.

CMakeLists.txt

@@ -88,6 +88,7 @@ set(SQLB_MOC_HDR
 	src/SqlUiLexer.h
 	src/FileDialog.h
 	src/ColumnDisplayFormatDialog.h
+	src/FilterLineEdit.h
 )
 
 set(SQLB_SRC
@@ -118,6 +119,7 @@ set(SQLB_SRC
 	src/SqlUiLexer.cpp
 	src/FileDialog.cpp
 	src/ColumnDisplayFormatDialog.cpp
+	src/FilterLineEdit.cpp
 )
 
 set(SQLB_FORMS

src/FilterLineEdit.cpp

@@ -0,0 +1,70 @@
+#include "FilterLineEdit.h"
+
+#include <QTimer>
+#include <QKeyEvent>
+
+FilterLineEdit::FilterLineEdit(QWidget* parent, QList<FilterLineEdit*>* filters, int columnnum) : QLineEdit(parent), filterList(filters), columnNumber(columnnum)
+{
+    setPlaceholderText(tr("Filter"));
+#if QT_VERSION >= QT_VERSION_CHECK(5, 2, 0)
+    setClearButtonEnabled(true);
+#endif
+    setProperty("column", columnnum);            // Store the column number for later use
+
+    // Introduce a timer for delaying the signal triggered whenever the user changes the filter value.
+    // The idea here is that the textChanged() event isn't connected to the update filter slot directly anymore
+    // but instead there this timer mechanism in between: whenever the user changes the filter the delay timer
+    // is (re)started. As soon as the user stops typing the timer has a chance to trigger and call the
+    // delayedSignalTimerTriggered() method which then stops the timer and emits the delayed signal.
+    delaySignalTimer = new QTimer(this);
+    delaySignalTimer->setInterval(300);         // This is the milliseconds of not-typing we want to wait before triggering
+    connect(this, SIGNAL(textChanged(QString)), delaySignalTimer, SLOT(start()));
+    connect(delaySignalTimer, SIGNAL(timeout()), this, SLOT(delayedSignalTimerTriggered()));
+
+    // Immediately emit the delayed filter value changed signal if the user presses the enter or the return key or
+    // the line edit widget loses focus
+    connect(this, SIGNAL(editingFinished()), this, SLOT(delayedSignalTimerTriggered()));
+}
+
+void FilterLineEdit::delayedSignalTimerTriggered()
+{
+    // Stop the timer first to avoid triggering in intervals
+    delaySignalTimer->stop();
+
+    // Emit the delayed signal using the current value
+    emit delayedTextChanged(text());
+}
+
+void FilterLineEdit::keyReleaseEvent(QKeyEvent* event)
+{
+    if(event->key() == Qt::Key_Tab)
+    {
+        if(columnNumber < filterList->size() - 1)
+        {
+            filterList->at(columnNumber + 1)->setFocus();
+            event->accept();
+        }
+    } else if(event->key() == Qt::Key_Backtab) {
+        if(columnNumber > 0)
+        {
+            filterList->at(columnNumber - 1)->setFocus();
+            event->accept();
+        }
+    }
+}
+
+void FilterLineEdit::clear()
+{
+    // When programatically clearing the line edit's value make sure the effects are applied immediately, i.e.
+    // bypass the delayed signal timer
+    QLineEdit::clear();
+    delayedSignalTimerTriggered();
+}
+
+void FilterLineEdit::setText(const QString& text)
+{
+    // When programatically setting the line edit's value make sure the effects are applied immediately, i.e.
+    // bypass the delayed signal timer
+    QLineEdit::setText(text);
+    delayedSignalTimerTriggered();
+}

src/FilterLineEdit.h

@@ -0,0 +1,36 @@
+#ifndef FILTERLINEEDIT_H
+#define FILTERLINEEDIT_H
+
+#include <QLineEdit>
+#include <QList>
+
+class QTimer;
+class QKeyEvent;
+
+class FilterLineEdit : public QLineEdit
+{
+    Q_OBJECT
+
+public:
+    explicit FilterLineEdit(QWidget* parent, QList<FilterLineEdit*>* filters, int columnnum);
+
+    // Override methods for programatically changing the value of the line edit
+    void clear();
+    void setText(const QString& text);
+
+private slots:
+    void delayedSignalTimerTriggered();
+
+signals:
+    void delayedTextChanged(QString text);
+
+protected:
+    void keyReleaseEvent(QKeyEvent* event);
+
+private:
+    QList<FilterLineEdit*>* filterList;
+    int columnNumber;
+    QTimer* delaySignalTimer;
+};
+
+#endif

src/FilterTableHeader.cpp

@@ -1,46 +1,8 @@
 #include "FilterTableHeader.h"
+#include "FilterLineEdit.h"
 
-#include <QLineEdit>
 #include <QTableView>
 #include <QScrollBar>
-#include <QKeyEvent>
-#include <QDebug>
-
-class FilterLineEdit : public QLineEdit
-{
-public:
-    explicit FilterLineEdit(QWidget* parent, QList<FilterLineEdit*>* filters, int columnnum) : QLineEdit(parent), filterList(filters), columnNumber(columnnum)
-    {
-        setPlaceholderText(tr("Filter"));
-#if QT_VERSION >= QT_VERSION_CHECK(5, 2, 0)
-        setClearButtonEnabled(true);
-#endif
-        setProperty("column", columnnum);            // Store the column number for later use
-    }
-
-protected:
-    void keyReleaseEvent(QKeyEvent* event)
-    {
-        if(event->key() == Qt::Key_Tab)
-        {
-            if(columnNumber < filterList->size() - 1)
-            {
-                filterList->at(columnNumber + 1)->setFocus();
-                event->accept();
-            }
-        } else if(event->key() == Qt::Key_Backtab) {
-            if(columnNumber > 0)
-            {
-                filterList->at(columnNumber - 1)->setFocus();
-                event->accept();
-            }
-        }
-    }
-
-private:
-    QList<FilterLineEdit*>* filterList;
-    int columnNumber;
-};
 
 FilterTableHeader::FilterTableHeader(QTableView* parent) :
     QHeaderView(Qt::Horizontal, parent)
@@ -78,7 +40,7 @@ void FilterTableHeader::generateFilters(int number, bool showFirst)
             l->setVisible(false);
         else
             l->setVisible(true);
-        connect(l, SIGNAL(textChanged(QString)), this, SLOT(inputChanged(QString)));
+        connect(l, SIGNAL(delayedTextChanged(QString)), this, SLOT(inputChanged(QString)));
         filterWidgets.push_back(l);
     }
 

src/src.pro

@@ -52,7 +52,8 @@ HEADERS += \
     ExportSqlDialog.h \
     SqlUiLexer.h \
     FileDialog.h \
-    ColumnDisplayFormatDialog.h
+    ColumnDisplayFormatDialog.h \
+    FilterLineEdit.h
 
 SOURCES += \
     sqlitedb.cpp \
@@ -80,7 +81,8 @@ SOURCES += \
     ExportSqlDialog.cpp \
     SqlUiLexer.cpp \
     FileDialog.cpp \
-    ColumnDisplayFormatDialog.cpp
+    ColumnDisplayFormatDialog.cpp \
+    FilterLineEdit.cpp
 
 RESOURCES += icons/icons.qrc \
              translations/flags/flags.qrc \