Button控制图片显示隐藏

package com.example.hades.demo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
ImageView img;
Button bt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
img = (ImageView)findViewById(R.id.imageView);
bt = (Button)findViewById(R.id.button);
bt.setOnClickListener(new click());
}

private class click implements View.OnClickListener {
@Override
public void onClick(View v) {
if (img.isShown()) {
img.setVisibility(View.INVISIBLE);
bt.setText("show");
} else {
img.setVisibility(View.VISIBLE);
bt.setText("fade");
}
}
}
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.hades.demo.MainActivity">

<LinearLayout
android:layout_width="368dp"
android:layout_height="495dp"
android:orientation="vertical"
tools:layout_editor_absoluteY="8dp"
tools:layout_editor_absoluteX="8dp">

<ImageView
android:id="@+id/imageView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:srcCompat="@mipmap/header" />

<Button
android:id="@+id/button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Button" />
</LinearLayout>
</android.support.constraint.ConstraintLayout>