一直跳錯  有勞幫忙看看了!  謝謝

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package com.example.user.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.CompoundButton;
import android.widget.ImageView;
import android.widget.ToggleButton;

public class MainActivity extends AppCompatActivity implements CompoundButton.OnCheckedChangeListener {
   private ToggleButton tv;
   private ImageView    img;
   private boolean isChecked;

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

      tv = (ToggleButton) findViewById(R.id.toggleButton);
      img=(ImageView) findViewById(R.id.imageView1);


       tv.setOnCheckedChangeListener(this);
   }

   @Override
   public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
       img.setBackgroundResource(isChecked?R.drawable.on:R.drawable.off);
   }
}