Proper null check to allow nullptr though

[tlf30]

Hello @SpaiR,
I would like to perform a null check to allow passing a null pointer through to native code.
Example:

public static native void openDialog(String vKey, String vTitle, String vFilters, String vPath, String vFileName,
                                         int vCountSelectionMax, long vUserDatas, int vFlags); /*
       if (env->IsSameObject(obj_vFilters, NULL)) {
            ImGuiFileDialog::Instance()->OpenDialog(vKey, vTitle, nullptr, vPath, vFileName, vCountSelectionMax, reinterpret_cast<void*>(vUserDatas), vFlags);
        } else {
            char* filters = (char*)env->GetStringUTFChars(obj_vFilters, JNI_FALSE);
            ImGuiFileDialog::Instance()->OpenDialog(vKey, vTitle, filters, vPath, vFileName, vCountSelectionMax, reinterpret_cast<void*>(vUserDatas), vFlags);
            env->ReleaseStringUTFChars(obj_vFilters, filters);
        }
    */

But the build system is still generating the char* vFilters = (char*)env->GetStringUTFChars(obj_vFilters, 0);, which causes an access violation when vFilters is null. I saw elsewhere in the library a check that uses obj_name == NULL, but this is not a safe way to check for a null as jni can have an object that is flagged as null, but not equal to null in the situation of a weak reference.

JNIEXPORT void JNICALL Java_imgui_extension_imguifiledialog_ImGuiFileDialog_openDialog(JNIEnv* env, jclass clazz, jstring obj_vKey, jstring obj_vTitle, jstring obj_vFilters, jstring obj_vPath, jstring obj_vFileName, jint vCountSelectionMax, jlong vUserDatas, jint vFlags) {
	char* vKey = (char*)env->GetStringUTFChars(obj_vKey, 0);
	char* vTitle = (char*)env->GetStringUTFChars(obj_vTitle, 0);
	char* vFilters = (char*)env->GetStringUTFChars(obj_vFilters, 0);
	char* vPath = (char*)env->GetStringUTFChars(obj_vPath, 0);
	char* vFileName = (char*)env->GetStringUTFChars(obj_vFileName, 0);


//@line:50

        if (env->IsSameObject(obj_vFilters, NULL)) {
            ImGuiFileDialog::Instance()->OpenDialog(vKey, vTitle, nullptr, vPath, vFileName, vCountSelectionMax, reinterpret_cast<void*>(vUserDatas), vFlags);
        } else {
            char* filters = (char*)env->GetStringUTFChars(obj_vFilters, JNI_FALSE);
            ImGuiFileDialog::Instance()->OpenDialog(vKey, vTitle, filters, vPath, vFileName, vCountSelectionMax, reinterpret_cast<void*>(vUserDatas), vFlags);
            env->ReleaseStringUTFChars(obj_vFilters, filters);
        }
    
	env->ReleaseStringUTFChars(obj_vKey, vKey);
	env->ReleaseStringUTFChars(obj_vTitle, vTitle);
	env->ReleaseStringUTFChars(obj_vFilters, vFilters);
	env->ReleaseStringUTFChars(obj_vPath, vPath);
	env->ReleaseStringUTFChars(obj_vFileName, vFileName);

}

Is there a way to prevent the build system from generating the char* vFilters = (char*)env->GetStringUTFChars(obj_vFilters, 0); and env->ReleaseStringUTFChars(obj_vFilters, vFilters);?

Thanks,
Trevor

[SpaiR]

Yes. Add a "MANUAL" marker to the method definition. Thus no auto-generation will be applied to the method args.
https://github.com/SpaiR/imgui-java/blob/master/imgui-binding/src/main/java/imgui/ImGui.java#L837

[tlf30]

Got it, thanks! See #98