無法解析JNIfunction：Android ndk

Question

我想通過從C++代碼中調用Android方法來獲取Android中已安裝應用程序的列表。找到第一個方法（getPackageManager()），但getInstalledApplications()方法每次都是零。這裏有什麼問題？

JNIEXPORT jobject JNICALL Java_com_example_davidt_ndkexample_TestNdk_getListOfInstalledApps 
    (JNIEnv* env, jobject obj, jobject activity){ 
    jclass contextWrapperClass = env->FindClass("android/content/ContextWrapper"); 
    jmethodID getPackageManagerId = env->GetMethodID(contextWrapperClass,"getPackageManager","()Landroid/content/pm/PackageManager;"); 
    if (getPackageManagerId == 0) { 
     fprintf(stderr, "packageManager() not found"); 
    } 

    jobject pm = env->CallObjectMethod(activity, getPackageManagerId); 

    jclass PackageManagerClass = env->GetObjectClass(pm); 
    jmethodID getInstalledApplicationsId = env->GetMethodID(PackageManagerClass,"getInstalledApplications","(I)[Landroid/content/pm/ApplicationInfo;"); 
    if (getInstalledApplicationsId == 0) { 
     fprintf(stderr, "getInstalledApplications() not found"); 
    } 

    return env->CallObjectMethod(pm, getInstalledApplicationsId); 
} 

Answer 1

看起來你的簽名描述符是錯誤的。我用javap的工具進行檢查，

javap -s -bootclasspath <Your SDK Installation Path>/platforms/android-25/android.jar android.content.pm.PackageManager 

和getInstalledApplications返回

public abstract java.util.List<android.content.pm.ApplicationInfo> getInstalledApplications(int); 
    descriptor: (I)Ljava/util/List; 

所以，在你的情況下，它必須是

jmethodID getInstalledApplicationsId = env->GetMethodID(PackageManagerClass,"getInstalledApplications","(I)Ljava/util/List");