Checking whether package is installed on android device in JNI C

Question

I wanted to check whether specific set of packages are installed on the device in c++ ndk code as I don't wanted to check in Java code, so after research I had written code comparing code in java. My code checks packageinfo and if exception is thrown it treats it as package not found. Here is my code snippet

jboolean
checkpackages(JNIEnv *env, jobject context, char packagePaths[][MAX_STRING_SIZE], int size) {

    jstring packageName;
    jobject packageManagerObj;
    jobject packageInfoObj;
    jclass contextClass = env->GetObjectClass(context);
    jmethodID getPackageNameMid = env->GetMethodID(contextClass, "getPackageName",
                                                   "()Ljava/lang/String;");
    jmethodID getPackageManager = env->GetMethodID(contextClass, "getPackageManager",
                                                   "()Landroid/content/pm/PackageManager;");
    jclass packageManagerClass = env->FindClass("android/content/pm/PackageManager");
    jmethodID getPackageInfo = env->GetMethodID(packageManagerClass, "getPackageInfo",
                                                "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");
    jclass packageInfoClass = env->FindClass("android/content/pm/PackageInfo");
    jfieldID versionCodeFid = env->GetFieldID(packageInfoClass, "versionCode", "I");
    packageManagerObj = env->CallObjectMethod(context, getPackageManager);
    for (int i = 0; i < size; i++) {
        const char *path = packagePaths[i];
        //packageName = env->NewStringUTF(path);

         jstring packageNamet = env->NewStringUTF("com.mypackgage");
        packageInfoObj = env->CallObjectMethod(packageManagerObj, getPackageInfo, packageNamet, 0x0);
        int versionCode = env->GetIntField(packageInfoObj, versionCodeFid);
        if(env->ExceptionCheck()) {
            env->ExceptionClear();

            __android_log_print(ANDROID_LOG_DEBUG, DEBUG_TAG, "NATIVE: Package manager: Exception");
        } else {
              return true;
        }
    }

    return false;
}

Here even after putting exception check my code crashes with pending exception

JNI DETECTED ERROR IN APPLICATION: JNI GetIntField called with pending exception android.content.pm.PackageManager$NameNotFoundException

My code works if I put existing package on device.I'm using Android studio 4.0.1 and ndk 21.3. Please help me in how can I handle this or any other way we can do.

Michael · Accepted Answer · 2020-09-25 07:36:59Z

0

As the documentation for getPackageInfo says, it can throw a NameNotFoundException.

You don't check for any exceptions until after GetIntField, which means that you might end up calling GetIntField with a pending exceptions, which isn't allowed.

answered Sep 25, 2020 at 7:36

Michael

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4 Comments

Mario Over a year ago

I had put code in try{}catch(std::exception){} but it was not working so I searched and got that to handle exception in ndk we should use if(env->ExceptionCheck()) { env->ExceptionClear(); //to clear exception before any other ndk code is run. } so used it in the code.

Michael Over a year ago

Like I said, you're not checking for Java exceptions until after GetIntField, but the CallObjectMethod just before it can throw an exception, and it is an error to call JNI functions with a pending Java exception. You need to check for and handle Java exceptions after every JNI call that can throw an exception.

Mario Over a year ago

Yes Michael, as I have mentioned in my above comment I have added code int versionCode = env->GetIntField(packageInfoObj, versionCodeFid); in try catch block but it was not going in catch block so after researching I came to know that to handle exception in ndk JNI c we have to check just below the statement that may result in exception if exception has occured by using statement env->ExceptionCheck(). try catch block doesn't get executed. Refered developer.com/java/data/exception-handling-in-jni.html

Michael Over a year ago

" in try catch block but it was not going in catch block" Because try/catch in C++ is for catching C++ exceptions. But what you're dealing with here are Java exceptions, which C++ has no idea about. Hence the need to use ExceptionCheck/Occurred/Clear. And again: checking for Java exceptions only after GetIntField is not enough. You need to do that after every single JNI call that might throw a Java exception.

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