ui: fixed crash that had a chance to occur when showing source files of cdb/cbp/sonargraph project

src/lib/CMakeLists.txt

@@ -595,6 +595,7 @@ add_files(
 	utility/ScopedFunctor.cpp
 	utility/ScopedFunctor.h
 	utility/ScopedSwitcher.h
+	utility/SingleValueCache.h
 	utility/TimeStamp.cpp
 	utility/TimeStamp.h
 	utility/tracing.cpp

src/lib/utility/SingleValueCache.h

@@ -0,0 +1,48 @@
+#ifndef SINGLE_VALUE_CACHE_H
+#define SINGLE_VALUE_CACHE_H
+
+#include <functional>
+
+template <typename ValType>
+class SingleValueCache
+{
+public:
+	SingleValueCache(std::function<ValType()> calculator);
+	ValType getValue();
+	void clear();
+
+private:
+	std::function<ValType()> m_calculator;
+	ValType m_value;
+	bool m_hasValue;
+};
+
+template <typename ValType>
+SingleValueCache<ValType>::SingleValueCache(std::function<ValType()> calculator)
+	: m_calculator(calculator)
+	, m_hasValue(false)
+{
+}
+
+template <typename ValType>
+ValType SingleValueCache<ValType>::getValue()
+{
+	if (!m_hasValue)
+	{
+		m_value = m_calculator();
+		m_hasValue = true;
+	}
+	return m_value;
+}
+
+template <typename ValType>
+void SingleValueCache<ValType>::clear()
+{
+	if (m_hasValue)
+	{
+		m_value = ValType();
+		m_hasValue = false;
+	}
+}
+
+#endif // SINGLE_VALUE_CACHE_H