Question

尝试构建我的第二个jni android应用程序并坚持到某一点。

这是我的基本示例包

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);
}

和我的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。但是当单击按钮时，项目异常停止。我试着看一下logcat日志。但无法理解错误背后的原因。发布logcat的几行

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)

我基本上试图实现当单击按钮时aPrivate的值更新并显示在textview中。从我的查找中可以清楚地看到所有错误都在jni实现中。

更新：

我已经跟踪了jni实现中两个位置发生的错误

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

如果我对这两行发表评论，则不会发生错误。

Answer 1

我在设置SetIntField时有点错误，它应该使用实例设置字段。

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

现在每件事都运作良好

jFieldId int对于对象无效

1 个答案: