Making a Android Toast via JNI, i.e. calling Java methods via JNI

Question

Concerning the outputting of an Toast, I found that there are some ways to make a Toast, that invoke calling a FindClass on JNIEnv object with the android/widget/Toast parameter, but I found no references in the code doing this.

I found this code here

jclass toast = (*env)->FindClass(env, "android/widget/Toast");
// ToastクラスのmakeTextスタティックメソッドのメソッドIDを取得する
jmethodID methodMakeText = (*env)->GetStaticMethodID(env, toast, "makeText", "(Landroid/content/Context;Ljava/lang/CharSequence;I)Landroid/widget/Toast;");
if(methodMakeText == NULL){
LOGE("toast.makeText not Found");

return;

But when using the strings tool on the C++ compiled files used in the app I'm decompiling, I haven't found any references to a Toast.

What other ways there are to call methods in a Java library, e.g. make a Toast?

Answer 1

You can try:

jclass toast = (*env)->FindClass(env, "android/widget/Toast"); // get the class you need (need to be already loaded otherwise you have to define it first)
jmethodID methodToCall = env->GetStaticMethodID(toast, "makeText", "(Landroid/content/Context;Ljava/lang/CharSequence;I)Landroid/widget/Toast;"); // get your desidered method

env->CallStaticVoidMethod(toast, methodToCall, <your parameters here>); // ask the jvm to call your method (assuming its static)