setOnClickListener Android Studio出错

Question

我想创建一个按钮，将webview重定向到某个页面。显示的错误是：'setOnclickListener之前从未使用'。我试过给 导入android.view.View.OnClickListener 但是没有用。

import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Button;
import android.widget.TextView;


import static sitesegundo.site.R.styleable.View;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //configuração do icone no title bar
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setLogo(R.drawable.icon);
        getSupportActionBar().setDisplayUseLogoEnabled(true);

        // configuração webview
        setContentView(R.layout.activity_main);
        WebView webView = (WebView) findViewById(R.id.webView);
        webView.loadUrl("file:///android_asset/www/index.html");
        webView.getSettings().setJavaScriptEnabled(true);
        webView.setWebViewClient(new WebViewClient());
        webView.setWebChromeClient(new WebChromeClient());

        // configuracao subtitulo titlebar
        getSupportActionBar().setTitle("  Adote A4");
        //getSupportActionBar().setSubtitle("");


    }


    @Override

    public boolean onCreateOptionsMenu(Menu menu){
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return super.onCreateOptionsMenu(menu);
    }


    Button button = (Button)findViewById(R.id.adocao);

    button.setOnClickListener(new OnClickListener(Object arg0) {
        public void onClick(View arg0) {
            Intent viewIntent =
                    new Intent("android.intent.action.VIEW",
                            Uri.parse("http://www.stackoverflow.com/"));
            startActivity(viewIntent);
        }
    });



}