android js webview 交互

public class MainActivity extends AppCompatActivity {    WebView mWebView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mWebView = (WebView) findViewById(R.id.webView);        WebSettings webSettings = mWebView.getSettings();        // 设置与Js交互的权限        webSettings.setJavaScriptEnabled(true);        // 设置允许JS弹窗        webSettings.setJavaScriptCanOpenWindowsAutomatically(true);        mWebView.addJavascriptInterface(this, "app");//对应js中的app.xxx        // 先载入JS代码        mWebView.loadUrl("http://www.more-print.com/api/dealer/index");        mWebView.setWebViewClient(new WebViewClient(){            @Override            public boolean shouldOverrideUrlLoading(WebView view, String url) {                view.loadUrl(url);                return true;            }        });    }    @JavascriptInterface    public void scan(String msg){        //对应js中xxx.scan("")        Toast.makeText(this,msg,Toast.LENGTH_LONG).show();        //        mWebView.post(new Runnable() {            @Override            public void run() {                // 注意调用的JS方法名要对应上                // 调用javascript的callJS()方法                mWebView.loadUrl("javascript:orderContent("+"20171205"+")");            }        });    }}