Add variadic template overloads for QJniObject/Environment methods

This allows the compiler to deduce the template arguments based on the
provided method parameters, which we can then pass to the methodSignature
and fieldSignature helpers to generate the signature string completely at
compile time.

Since we can't partially specialize template member functions, replace
the specializations for void methods with compile-time-if branches in
the general templates.

This variadic template now prevents implicit conversion from the
LiteralStorage types to const char* signatures, so catch the case where
such a type ends up in the parameter list.

Due to overload resolution rules for constructors, we need to explicitly
disable the constructor if any of the arguments is a string literal type,
as we have to keep the old C-style variadic function working for such
calls.

Add variations that use the variadic templates to the unit tests.

Change-Id: I8734664b38bae932369462330a9a03302254c33c
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

1 files changed, 50 insertions, 1 deletions

diff --git a/src/corelib/kernel/qjnienvironment.cpp b/src/corelib/kernel/qjnienvironment.cpp
index 9766ff4d3b..3eab31bbc2 100644
--- a/src/corelib/kernel/qjnienvironment.cpp
+++ b/src/corelib/kernel/qjnienvironment.cpp
@@ -232,6 +232,16 @@ jmethodID QJniEnvironment::findMethod(jclass clazz, const char *methodName, cons
 }
 
 /*!
+    \fn template<typename ...Args> jmethodId QJniEnvironment::findMethod(jclass clazz, const char *methodName)
+    \since 6.4
+
+    Searches for an instance method of a class \a clazz. The method is specified
+    by its \a methodName, the signature is deduced from the template parameters.
+
+    Returns the method ID or \c nullptr if the method is not found.
+*/
+
+/*!
     Searches for a static method of a class \a clazz. The method is specified
     by its \a methodName and \a signature.
 
@@ -265,9 +275,28 @@ jmethodID QJniEnvironment::findStaticMethod(jclass clazz, const char *methodName
     return nullptr;
 }
 
+/*!
+    \fn template<typename ...Args> jmethodId QJniEnvironment::findStaticMethod(jclass clazz, const char *methodName)
+    \since 6.4
+
+    Searches for an instance method of a class \a clazz. The method is specified
+    by its \a methodName, the signature is deduced from the template parameters.
+
+    Returns the method ID or \c nullptr if the method is not found.
+
+    \code
+    QJniEnvironment env;
+    jclass javaClass = env.findClass("org/qtproject/example/android/CustomClass");
+    jmethodID methodId = env.findStaticMethod<void, jstring>(javaClass, "staticJavaMethod");
+    QJniObject javaMessage = QJniObject::fromString("findStaticMethod example");
+    QJniObject::callStaticMethod<void>(javaClass,
+                                       methodId,
+                                       javaMessage.object<jstring>());
+    \endcode
+*/
 
 /*!
-    Searches for an member field of a class \a clazz. The field is specified
+    Searches for a member field of a class \a clazz. The field is specified
     by its \a fieldName and \a signature.
 
     Returns the field ID or \c nullptr if the field is not found.
@@ -289,6 +318,16 @@ jfieldID QJniEnvironment::findField(jclass clazz, const char *fieldName, const c
 }
 
 /*!
+    \fn template<typename T> jfieldID QJniEnvironment::findField(jclass clazz, const char *fieldName)
+    \since 6.4
+
+    Searches for a member field of a class \a clazz. The field is specified
+    by its \a fieldName. The signature of the field is deduced from the template parameter.
+
+    Returns the field ID or \c nullptr if the field is not found.
+*/
+
+/*!
     Searches for a static field of a class \a clazz. The field is specified
     by its \a fieldName and \a signature.
 
@@ -311,6 +350,16 @@ jfieldID QJniEnvironment::findStaticField(jclass clazz, const char *fieldName, c
 }
 
 /*!
+    \fn template<typename T> jfieldID QJniEnvironment::findStaticField(jclass clazz, const char *fieldName)
+    \since 6.4
+
+    Searches for a static field of a class \a clazz. The field is specified
+    by its \a fieldName. The signature of the field is deduced from the template parameter.
+
+    Returns the field ID or \c nullptr if the field is not found.
+*/
+
+/*!
     \fn JavaVM *QJniEnvironment::javaVM()
 
     Returns the Java VM interface for the current process. Although it might