Question

我在Android中编写了一个c-jni函数，我在创建Long-object时遇到了问题。我成功调用了构造函数，但是当我用longValue读取对象的值时，我得到了错误的结果。

jmethodID longConstructor;
jmethodID longGetLongValue;
jclass cls;
jobject obj;

// Create a object of type Long.
cls = (*env)->FindClass(env,"java/lang/Long");
longConstructor = (*env)->GetMethodID(env,cls,"<init>","(J)V");
obj = (*env)->NewObject(env, cls, longConstructor, 4242);

// Get the value by calling the function longValue.
longGetLongValue= (*env)->GetMethodID(env,cls,"longValue","()J");
long return_long_value = (*env)->CallLongMethod(env, obj, longGetLongValue);

// Log the result.
LOGD("%li",  return_long_value);

我希望上面的代码会在日志中打印4242，但是日志中打印的值是1691768.

有没有人知道为什么4242没有写入日志？

Answer 1

＆lt; jni.h＆gt; 声明

typedef long long       jlong;          /* signed 64 bits */

因此，这是修复：

obj = (*env)->NewObject(env, cls, longConstructor, (jlong)4242); // or 4242ll

longGetLongValue= (*env)->GetMethodID(env,cls,"longValue","()J");
long return_long_value = (*env)->CallLongMethod(env, obj, longGetLongValue);
jlong return_jlong_value = (*env)->CallLongMethod(env, obj, longGetLongValue);

__android_log_print(ANDROID_LOG_DEBUG, "test", "native t = %ld",  return_long_value);
__android_log_print(ANDROID_LOG_DEBUG, "test", "native t = %lld",  return_jlong_value);

Answer 2

如果你看一下JNI映射类型，C中的long等同于jint，因此我认为你应该使用java / lang / Integer而不是java / lang / Long。

// Create a object of type Integer
jclass cls = (*env)->FindClass(env, "java/lang/Integer");
jmethodID constructorId = (*env)->GetMethodID(env, cls, "<init>", "(I)V");
jobject o = (*env)->NewObject(env, cls, constructorId, 4242);

// Get the value by calling the function intValue.
jmethodID intValueMethodId = (*env)->GetMethodID(env, cls, "intValue", "()I");
long val = (*env)->CallIntMethod(env, obj, intValueMethodId);

// Log the result.
LOGD("%d",  val);

JNI：使用错误值创建的长对象

2 个答案: