From ceab71c3a933952e4223830f727f0ba4f67d1b2c Mon Sep 17 00:00:00 2001
From: Gustavo Niemeyer <gustavo@niemeyer.net>
Date: Thu, 12 Sep 2013 17:20:34 -0300
Subject: [PATCH] Go gets the result from calling QML methods.

---
 all_test.go  | 4 ++--
 cpp/capi.cpp | 5 +++--
 cpp/capi.h   | 2 +-
 datatype.go  | 3 +++
 qml.go       | 9 ++++++---
 5 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/all_test.go b/all_test.go
index 2e3e273f..9f45ac63 100644
--- a/all_test.go
+++ b/all_test.go
@@ -415,8 +415,8 @@ var tests = []struct {
 	},
 	{
 		Summary: "Call a QML method from Go",
-		QML:     `Item { function f() { console.log("f was called") } }`,
-		Done:    func(d *TestData) { d.compinst.Call("f") },
+		QML:     `Item { function f() { console.log("f was called"); return "<result>"; } }`,
+		Done:    func(d *TestData) { d.Check(d.compinst.Call("f"), Equals, "<result>") },
 		DoneLog: "f was called",
 	},
 }
diff --git a/cpp/capi.cpp b/cpp/capi.cpp
index 9f47e3c5..63d31403 100644
--- a/cpp/capi.cpp
+++ b/cpp/capi.cpp
@@ -204,13 +204,14 @@ void objectGetProperty(QObject_ *object, const char *name, DataValue *value)
     packDataValue(&var, value);
 }
 
-void objectInvoke(QObject_ *object, const char *method)
+void objectInvoke(QObject_ *object, const char *method, DataValue *resultdv)
 {
     QObject *qobject = reinterpret_cast<QObject *>(object);
 
-    // TODO Support parameters and result.
+    // TODO Parameter support.
     QVariant result;
     QMetaObject::invokeMethod(qobject, method, Qt::DirectConnection, Q_RETURN_ARG(QVariant, result));
+    packDataValue(&result, resultdv);
 }
 
 void objectSetParent(QObject_ *object, QObject_ *parent)
diff --git a/cpp/capi.h b/cpp/capi.h
index 71286c8b..9f1f1541 100644
--- a/cpp/capi.h
+++ b/cpp/capi.h
@@ -107,7 +107,7 @@ void contextSetObject(QQmlContext_ *context, QObject_ *value);
 void delObject(QObject_ *object);
 void objectGetProperty(QObject_ *object, const char *name, DataValue *value);
 void objectSetParent(QObject_ *object, QObject_ *parent);
-void objectInvoke(QObject_ *object, const char *method);
+void objectInvoke(QObject_ *object, const char *method, DataValue *result);
 
 QQmlComponent_ *newComponent(QQmlEngine_ *engine, QObject_ *parent);
 void componentSetData(QQmlComponent_ *component, const char *data, int dataLen, const char *url, int urlLen);
diff --git a/datatype.go b/datatype.go
index acae6990..47ad3f8b 100644
--- a/datatype.go
+++ b/datatype.go
@@ -89,6 +89,9 @@ func packDataValue(value interface{}, dvalue *C.DataValue, engine *Engine, owner
 }
 
 // unpackDataValue converts a value shipped by C++ into a native Go value.
+//
+// HEADS UP: This is considered safe to be run out of the main GUI thread.
+//           If that changes, fix the call sites.
 func unpackDataValue(dvalue *C.DataValue) interface{} {
 	datap := unsafe.Pointer(&dvalue.data)
 	switch dvalue.dataType {
diff --git a/qml.go b/qml.go
index 93435e1e..7af4232e 100644
--- a/qml.go
+++ b/qml.go
@@ -285,14 +285,17 @@ func (o *commonObject) Field(name string) interface{} {
 	return unpackDataValue(&value)
 }
 
-func (o *commonObject) Call(method string) {
-	// TODO Support parameters and result.
+func (o *commonObject) Call(method string) interface{} {
+	// TODO Parameter support.
+	// TODO What about errors?
+	var result C.DataValue
 	gui(func() {
 		// TODO Do not allocate this string every time.
 		name := C.CString(method)
 		defer C.free(unsafe.Pointer(name))
-		C.objectInvoke(o.addr, name)
+		C.objectInvoke(o.addr, name, &result)
 	})
+	return unpackDataValue(&result)
 }
 
 // Destroy finalizes the value and releases any resources used.