After hours of struggling with small bugs in JNI code I got tired and wrote these variadic template wrappers for cocos2d-x JniHelper to make calling Java from C++ nice and easy
Here’s an example. Suppose we have a Java class
class Logger {
public static void purchase(float sum, String currency) {
// some code here
}
}
Then we can call it from C++ with just one line of code
easyjni::callVoidMethod("path/to/Logger", "purchase", float(3.14), "USD");
There can be any number of arguments and the method signature is automatically inferred under the hood with template magic. Supported argument data types are: bool, char, short, int, long, float, double, char* and std::string. Make sure the arguments on the Java side have corresponding primitive types (no Boolean, Integer, etc), except for char* and std::string, corresponding Java type for them is String.
One thing to note is that it should be obvious for the compiler to infer template types, otherwise incorrect signature might be generated and JNI won’t be able to find the method you are trying to call. This can be achieved with three different approaches:
-
Using variables as parameters, i.e.
float sum = 3.14;
std::string currency = “USD”;
easyjni::callVoidMethod(“path/to/Logger”, “purchase”, sum, currency); -
With implicit casts:
easyjni::callVoidMethod(“path/to/Logger”, “purchase”, float(3.14), “USD”);
-
And with implicit template instantiation
easyjni::callVoidMethod<float, std::string>(“path/to/Logger”, “purchase”, 3.14, “USD”);
This should be integrated into cocos2dx. Could you make a pr for this.
This code was actually merged into master about a year ago