jFieldId int对一个对象无效

尝试构建我的第二个jni android应用程序并坚持一个点。jFieldId int对一个对象无效

这是我的基本的例子包

package com.example.angelica.myapplication; 


public class SomeVars { 
    //load library 

    public int aPrivate; 

    public native void UpdateVars(); 
}

和我的JNI实现

#include <jni.h> 

extern "C" 
JNIEXPORT void JNICALL 
Java_com_example_angelica_myapplication_SomeVars_UpdateVars(JNIEnv *env, jobject instance) { 

    // TODO 
    jclass cls = getclass(); 
    jfieldID fid = getField("aPrivate"); 

    jint i = env->GetIntField(cls,fid); 

    i = i + 100; 
    env->SetIntField(cls, fid,i); 
}

和我MainActivity.java文件

public class MainActivity extends AppCompatActivity { 

    TextView tv; 
    SomeVars var = new SomeVars(); 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     tv = (TextView) findViewById(R.id.sample_text); 

     var.aPrivate = 23; 
     if (var.aPrivate == 23) { 
      tv.setText("23"); 
     }else { 
      tv.setText("Two Hunderd"); 
     } 

     Button button = (Button)findViewById(R.id.button); 
     button.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 

       var.UpdateVars(); 

       if (var.aPrivate == 23) { 
        tv.setText("23"); 
       }else { 
        tv.setText("Changed"); 
       } 
      } 
     }); 
    } 
}

项目构建成功，并正确启动。但是当按钮被点击时，项目会异常停止。我试图看看logcat日志。但无法理解错误背后的原因。发布的logcat的

04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] JNI DETECTED ERROR IN APPLICATION: jfieldID int com.example.angelica.myapplication.SomeVars.aPrivate not valid for an object of class java.lang.Class<com.example.angelica.myapplication.SomeVars> 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470]  in call to GetIntField 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470]  from void com.example.angelica.myapplication.SomeVars.UpdateVars() 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] "main" prio=5 tid=1 Runnable 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] | group="main" sCount=0 dsCount=0 obj=0x7449df60 self=0xa968b400 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] | sysTid=3949 nice=-10 cgrp=default sched=0/0 handle=0xada11534 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] | state=R schedstat=(0 0 0) utm=4 stm=18 core=1 HZ=100 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] | stack=0xbf5fe000-0xbf600000 stackSize=8MB 
04-16 13:34:56.171 3949-3949/com.example.angelica.myapplication A/art: art/runtime/java_vm_ext.cc:470] | held mutexes= "mutator lock"(shared held)

我基本上是试图单击时按钮被aPrivate的值更新和TextView的显示来实现的几行。从我的查询中可以明显看出，所有错误都是在jni实现中。

更新：

我在JNI实现

jint i = env->GetIntField(cls,fid); //Error 1 
env->SetIntField(cls, fid,200);  //Error 2

追查这是发生误差在两个位置。如果我评论这两个线路没有错误发生。

来源

2017-04-16 Angelica

我在设置SetIntField时有点不对，应该使用实例设置字段。

env->SetIntField(cls, fid,200);  //Error 
env->SetIntField(instance, fid, 200); //SOLVED

现在，每一件事情是工作好

来源

2017-04-16 08:53:28 Angelica

jFieldId int对一个对象无效

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