使用String参数调用时JNI崩溃 [英] JNI crash when called with a String argument

问题描述

我试图从我的Android代码中调用用C实现的函数.代码流是这样的:

I am trying to call a function implemented in C from my Android code. The code flow is this:

在我的主要活动的onCreate()中，我有这个:

In the onCreate() of my main activity, I have this:

    TestClass tc = new TestClass();
    tc.act();

这是TestClass:

This is TestClass:

package bar.foo;

public class TestClass {
    static {
        System.loadLibrary("testclass");
    }
    public native void doStuff1(String s);
    public native void doStuff2(String s1, String s2);

    TestClass() { }
    public void act() {
        doStuff1 ("Foo");
        doStuff2 ("Bar", "Baz");
    }
}

testclass.c是:

And testclass.c is:

#include <stdio.h>
#include <string.h>
#include <jni.h>
#include <android/log.h>

#define alprint __android_log_print

#define METHOD_SIGNATURE_1 Java_bar_foo_TestClass_doStuff1
#define METHOD_SIGNATURE_2 Java_bar_foo_TestClass_doStuff2

void METHOD_SIGNATURE_1(JNIEnv* env, jstring s) {

    const char *ns;
    int jsLen;

    /* Extract strings */
    ns = (*env)->GetStringUTFChars(env, s, NULL);
        jsLen = (*env)->GetStringUTFLength(env, s);

        alprint(6, "doStuff1", "Text = %s [%d]\n", ns, jsLen);

    (*env)->ReleaseStringUTFChars(env, s, ns);

        return;
}

void METHOD_SIGNATURE_2(JNIEnv* env, jstring s1, jstring s2) {

    const char *ns1;
    const char *ns2;
    int js1Len;
        int js2Len;

    /* Extract strings */
    ns1 = (*env)->GetStringUTFChars(env, s1, NULL);
        js1Len = (*env)->GetStringUTFLength(env, s1);
        ns2 = (*env)->GetStringUTFChars(env, s2, NULL);
        js2Len = (*env)->GetStringUTFLength(env, s2);

        alprint(6, "doStuff2", "Text(1) = %s [%d]\n", ns1, js1Len);
        alprint(6, "doStuff2", "Text(2) = %s [%d]\n", ns2, js2Len);

    (*env)->ReleaseStringUTFChars(env, s1, ns1);
    (*env)->ReleaseStringUTFChars(env, s2, ns2);

        return;
}

这可以很好地编译，并且可以在我的Android设备(运行Android 5.1的Nexus 5)上启动，但是在启动时崩溃:

This compiles fine, and launches on my Android device (a Nexus 5 running Android 5.1) but crashes upon launch with:

JNI DETECTED ERROR IN APPLICATION: jstring has wrong type: bar.foo.TestClass

完整的崩溃转储位于此处: http://pastebin.com/C0M98Uzb

The full crash dump is here: http://pastebin.com/C0M98Uzb

自昨天晚上以来，我一直在为此烦恼；有人知道这是怎么回事吗?

I have been breaking my head over this one since yesterday evening; does anyone know what this is about?

推荐答案

JNI函数中的第二个参数是对调用了本机方法的Java对象的引用(对于静态函数，则为类).因此，您只需要在函数声明中添加一个thiz参数:

The second parameter in a JNI function is a reference to the Java object the native method was called on (or the class in the case of a static function). So you just need to add a thiz parameter to your function declarations:

void METHOD_SIGNATURE_1(JNIEnv* env, jobject thiz, jstring s)
void METHOD_SIGNATURE_2(JNIEnv* env, jobject thiz, jstring s1, jstring s2)

这篇关于使用String参数调用时JNI崩溃的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！