Make qt wallet test compatible with qt4

Unlike Qt5, the Qt4 signals implementation doesn't allow a signal to be
directly connected to a c++ lambda expression. Work around this by defining a
Callback QObject with a virtual method that can forward calls to a closure.

The Qt4 error was reported by Patrick Strateman <patrick.strateman@gmail.com>
in https://github.com/bitcoin/bitcoin/pull/10039#issuecomment-289248763

1 files changed, 30 insertions, 0 deletions

diff --git a/src/qt/callback.h b/src/qt/callback.h
new file mode 100644
index 0000000000..a8b593a652
--- /dev/null
+++ b/src/qt/callback.h
@@ -0,0 +1,30 @@
+#ifndef BITCOIN_QT_CALLBACK_H
+#define BITCOIN_QT_CALLBACK_H
+
+#include <QObject>
+
+class Callback : public QObject
+{
+    Q_OBJECT
+public Q_SLOTS:
+    virtual void call() = 0;
+};
+
+template <typename F>
+class FunctionCallback : public Callback
+{
+    F f;
+
+public:
+    FunctionCallback(F f_) : f(std::move(f_)) {}
+    ~FunctionCallback() override {}
+    void call() override { f(this); }
+};
+
+template <typename F>
+FunctionCallback<F>* makeCallback(F f)
+{
+    return new FunctionCallback<F>(std::move(f));
+}
+
+#endif // BITCOIN_QT_CALLBACK_H