java - JNI NewStringUTF 调用时出现未决异常 'java.lang.NoSuchMethodError'

Question

我不知道为什么调用本地方法会抛出异常。

native 代码:

JNIEXPORT jstring JNICALL Java_org_amk_lockscreen_JNIActivity_getPackege(JNIEnv *env,jclass cls,jobject context){
    jclass Context_class = (*env).FindClass("android/content/Context");
    jmethodID midGetPackageName = (*env).GetMethodID(Context_class, "getPackageName", "(V)Ljava/lang/String;");
    if(midGetPackageName==0){
        return (*env).NewStringUTF("Not Found Method");
    }
    else{
        jobject packageName=(*env).CallObjectMethod( context, midGetPackageName);
        return (jstring)packageName;
    }
}

和我的java代码:

public class JNIActivity extends Activity {

    static {
        System.loadLibrary("myjni"); // "myjni.dll" in Windows, "libmyjni.so" in Unixes
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_jni);
        TextView txt = (TextView) findViewById(R.id.txtMessage);
        try {
            txt.setText(getPackege(getApplicationContext()));
        } catch (Exception exp) {
            txt.setText(exp.getMessage());
        }
    }

    public native String getMessage();

    public native String getPackege(Context con);
}

但是当运行这个时，它会抛出异常:

JNI DETECTED ERROR IN APPLICATION: JNI NewStringUTF called with pending exception 'java.lang.NoSuchMethodError' thrown in java.lang.String org.amk.lockscreen.JNIActivity.getPackege(android.content.Context):-2
in call to NewStringUTF
from java.lang.String org.amk.lockscreen.JNIActivity.getPackege(android.content.Context)

我测试了不同的方法签名，例如:

(Ljava/lang/Void;)Ljava/lang/String;     
   (V;)Ljava/lang/String;

但它再次抛出异常。

我哪里做错了？

Answer 1

GetMethodID 引发异常。您不会检查是否使用 env->ExceptionCheck(env) 引发了异常，然后使用 ExceptionClear() 清除它或立即从函数返回以便 JVM 处理它。请在此处查看有关 getMethodId 的 Oracle 文档:http://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/functions.html

例如(来自 http://www.ibm.com/developerworks/library/j-jni/ :) findClass、GetStaticMethodID 和 CallStaticVoidMethod 调用都生成类似于 GetMethodID 的异常。

int val=1;
jmethodID method;
jclass cls;

cls = (*env)->FindClass(env, "com/ibm/example/TestClass");
if ((*env)->ExceptionCheck(env)) {
   return ERR_FIND_CLASS_FAILED;
}
method = (*env)->GetStaticMethodID(env, cls, "setInfo", "(I)V");
if ((*env)->ExceptionCheck(env)) {
   return ERR_GET_STATIC_METHOD_FAILED;
}
(*env)->CallStaticVoidMethod(env, cls, method,val);
if ((*env)->ExceptionCheck(env)) {
   return ERR_CALL_STATIC_METHOD_FAILED;
}