java.lang.NoSuchFieldError： no "Ljava/lang/String;" field JNI

Question

您好。请告诉我我做错了什么。实现了从android/provider/Settings$System获取密钥。像ACCELEROMETER_ROTATION这样的按键看起来没有问题(这些描述https://developer.android.com/reference/android/provider/Settings.System)但像sms_deliveryd_sound一样，他拒绝搜索。写入错误。

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.woodman.testlibsettingsv2, PID: 31133
java.lang.NoSuchFieldError: no "Ljava/lang/String;" field "sms_delivered_sound" in class "Landroid/provider/Settings$System;" or its superclasses
at com.example.woodman.testlibsettingsv2.frmMain.GetSystemKyesString(Native Method)
at com.example.woodman.testlibsettingsv2.frmMain.onCreate(frmMain.java:32)
at android.app.Activity.performCreate(Activity.java:7210)
at android.app.Activity.performCreate(Activity.java:7201)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2926)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1831)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6806)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)

代码

extern "C"
JNIEXPORT jstring JNICALL
Java_com_example_woodman_testlibsettingsv2_frmMain_GetSystemKyesString(JNIEnv *env,
 jobject instance,
 jstring key_Name_) {
const char *key_Name = env->GetStringUTFChars(key_Name_, 0);
// TODO
jclass activityThread = env->FindClass("android/app/ActivityThread");
jmethodID currentActivityThread = env->GetStaticMethodID(activityThread,
"currentActivityThread",
"()Landroid/app/ActivityThread;");
jobject at = env->CallStaticObjectMethod(activityThread, currentActivityThread);
jmethodID getApplication = env->GetMethodID(activityThread, "getApplication",
"()Landroid/app/Application;");
jobject context = env->CallObjectMethod(at, getApplication);

jclass c_settings_system = env->FindClass("android/provider/Settings$System");
jclass c_context = env->FindClass("android/content/Context");
if (c_settings_system == NULL || c_context == NULL) {
return NULL;
}
jmethodID m_get_content_resolver = env->GetMethodID(c_context, "getContentResolver",
"()Landroid/content/ContentResolver;");
if (m_get_content_resolver == NULL) {
return NULL;
}
jfieldID f_android_string_key = env->GetStaticFieldID(c_settings_system,
key_Name,
"Ljava/lang/String;");
if (f_android_string_key == NULL) {
return NULL;
}
jstring s_android_string_key = (jstring) env->GetStaticObjectField(c_settings_system,
 f_android_string_key);

jobject o_content_resolver;
o_content_resolver = env->CallObjectMethod(context,
m_get_content_resolver);
if (o_content_resolver == NULL || s_android_string_key == NULL) {
return NULL;
}
jmethodID m_get_string = env->GetStaticMethodID(c_settings_system, "getString",
"(Landroid/content/ContentResolver;Ljava/lang/String;)Ljava/lang/String;");
if (m_get_string == NULL) {
return NULL;
}
jstring string_key = (jstring) env->CallStaticObjectMethod(c_settings_system,
 m_get_string,
 o_content_resolver,
 s_android_string_key);
return string_key;
}

感谢

Answer 1

此值不是系统设置的一部分。事实上，它可以在miui框架上找到，但在其他安卓系统中找不到。

没有公共的API可以读取此设置，C++和Java中都没有。但我们知道这个值是以简单的key=value格式写在system/build.prop文件中的。

这个文件人人都可读。您不需要JNI来读取它，通常的C++甚至C文件API都可以完美地工作。

更灵活的方法是从代码中运行settings命令。