JNI preliminary (3) update UI example

1. Write native methods in Activity

package com.godv.ccalljava;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

    public void showToa(View view) {
        toastCallBack();
    }

    public native void toastCallBack();
    
    public void showToast(){
        Log.i("godv","更新UI");
        Toast.makeText(this, "godv", Toast.LENGTH_SHORT).show();
    }
}

2. Generate .h file to rewrite the method in .c  

 JNIEXPORT void JNICALL Java_com_godv_ccalljava_MainActivity_toastCallBack
   (JNIEnv * env, jobject instance)
   {
       jclass jclazz = (*env)->FindClass(env,"com/godv/ccalljava/MainActivity");
       jmethodID jids = (*env)->GetMethodID(env,jclazz,"showToast","()V");
       (*env)->CallVoidMethod(env,instance,jids);
   }

3. Called in activity