jFieldId int對一個對象無效

嘗試構建我的第二個jni android應用程序並堅持一個點。jFieldId int對一個對象無效

這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實現

#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"); 
       } 
      } 
     }); 
    } 
}

項目構建成功，並正確啓動。但是當按鈕被點擊時，項目會異常停止。我試圖看看logcat日誌。但無法理解錯誤背後的原因。發佈的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)

我基本上是試圖單擊時按鈕被aPrivate的值更新和TextView的顯示來實現的幾行。從我的查詢中可以明顯看出，所有錯誤都是在jni實現中。

更新：

我在JNI實現

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

追查這是發生誤差在兩個位置。如果我評論這兩個線路沒有錯誤發生。

來源

2017-04-16 Angelica

我在設置SetIntField時有點不對，應該使用實例設置字段。

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

現在，每一件事情是工作好

來源

2017-04-16 08:53:28 Angelica

jFieldId int對一個對象無效

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