从android中的webview中提取单个变量？

public class WebAppInterface {
    Context mContext;

    WebAppInterface(Context c) {
        mContext = c;
    }

    @JavascriptInterface
    public void setVariable(String variable) {
        // 在这里处理变量
    }
}

WebView webView = (WebView) findViewById(R.id.webview);
webView.getSettings().setJavaScriptEnabled(true);
webView.addJavascriptInterface(new WebAppInterface(this), "Android");

    function setVariable(variable) {
        Android.setVariable(variable);
    }
</script>

webView.setWebViewClient(new WebViewClient() {
    @Override
    public void onPageFinished(WebView view, String url) {
        super.onPageFinished(view, url);
        view.evaluateJavascript("JavaScript代码", null);
    }
});

javascript: {
    var variable = document.getElementById("variable").value;
    Android.setVariable(variable);
}