JNI 对象操作-jnidui-xiang-cao-zuo.md

---

// 1.寻找类 Student
// jclass studentClass = env->FindClass("com/derry/as_jni_project/Student"); // 第一种
jclass studentClass = env->GetObjectClass(student); // 第二种

// 2.Student类里面的函数规则  签名
jmethodID setName = env->GetMethodID(studentClass, "setName", "(Ljava/lang/String;)V");
jmethodID getName = env->GetMethodID(studentClass, "getName", "()Ljava/lang/String;");
jmethodID showInfo = env->GetStaticMethodID(studentClass, "showInfo", "(Ljava/lang/String;)V");

// 3.调用 setName
jstring value = env->NewStringUTF("AAAA");
env->CallVoidMethod(student, setName, value);

// 4.调用 getName
jstring getNameResult = static_cast<jstring>(env->CallObjectMethod(student, getName));
const char *getNameValue = env->GetStringUTFChars(getNameResult, NULL);
LOGE("调用到getName方法，值是:%s\n", getNameValue);

// 5.调用静态showInfo
jstring jstringValue = env->NewStringUTF("静态方法你好，我是C++");
env->CallStaticVoidMethod(studentClass, showInfo, jstringValue);

}

运行结果：

I/JNISTUDY: strChar：九阳神功
D/Student: Java setName name:AAAA
E/JNISTUDY: 调用到getName方法，值是:AAAA
D/Student: showInfo info:静态方法你好，我是C++

# JNI创建JAVA对象

Java对象：

```java
import android.util.Log;

public class Student {

    private final static String TAG = Student.class.getSimpleName();

    public String name;
    public int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        Log.d(TAG, "Java setName name:" + name);
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        Log.d(TAG, "Java setAge age:" + age);
        this.age = age;
    }

    public static void showInfo(String info) {
        Log.d(TAG, "showInfo info:" + info);
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

import android.util.Log;

public class Person {

    private static final String TAG = Person.class.getSimpleName();

    public Student student;

    public void setStudent(Student student) {
        Log.d(TAG, "call setStudent student:" + student.toString());
        this.student = student;
    }

    public static void putStudent(Student student) {
        Log.d(TAG, "call static putStudent student:" + student.toString());
    }
}

JNI层

// C++ 堆 栈 ...
// JNI函数  局部引用，全局引用，...
extern "C"
JNIEXPORT void JNICALL
Java_com_derry_as_1jni_1project_MainActivity_insertObject(JNIEnv *env, jobject thiz) {
    /*jstring str = env->GetStringUTFChars();
    jstring str = env->GetStringUTFChars();
    jstring str = env->GetStringUTFChars();
    jstring str = env->GetStringUTFChars();
    jstring str = env->GetStringUTFChars();
    jstring str = env->GetStringUTFChars();
    jstring str = env->GetStringUTFChars();

    // 好习惯：
    // 我用完了，我记释放，在我函数执行过程中，不会导致 内存占用多
    env->ReleaseStringUTFChars()*/


    // 1.通过包名+类名的方式 拿到 Student class  凭空拿class
    const char *studentstr = "com/derry/as_jni_project/Student";
    jclass studentClass = env->FindClass(studentstr);

    // 2.通过student的class  实例化此Student对象   C++ new Student
    jobject studentObj = env->AllocObject(studentClass); // AllocObject 只实例化对象，不会调用对象的构造函数

    // 方法签名的规则
    jmethodID setName = env->GetMethodID(studentClass, "setName", "(Ljava/lang/String;)V");
    jmethodID setAge = env->GetMethodID(studentClass, "setAge", "(I)V");

    // 调用方法
    jstring strValue = env->NewStringUTF("Derry");
    env->CallVoidMethod(studentObj, setName, strValue);
    env->CallVoidMethod(studentObj, setAge, 99);


    // env->NewObject() // NewObject 实例化对象，会调用对象的构造函数


    // ====================  下面是 Person对象  调用person对象的  setStudent 函数等

    // 4.通过包名+类名的方式 拿到 Student class  凭空拿class
    const char *personstr = "com/derry/as_jni_project/Person";
    jclass personClass = env->FindClass(personstr);

    jobject personObj = env->AllocObject(personClass); // AllocObject 只实例化对象，不会调用对象的构造函数

    // setStudent 此函数的 签名 规则
    jmethodID setStudent = env->GetMethodID(personClass, "setStudent",
            "(Lcom/derry/as_jni_project/Student;)V");

    env->CallVoidMethod(personObj, setStudent, studentObj);

    // 规范：一定记得释放【好习惯】
    // 第一类
    env->DeleteLocalRef(studentClass);
    env->DeleteLocalRef(personClass);
    env->DeleteLocalRef(studentObj);
    env->DeleteLocalRef(personObj);

    // 第二类
    // env->ReleaseStringUTFChars()

    // TODO 局部引用： jobject jclass jstring ...  【函数结束后，会自动释放】
}