因为该方法的执行不会使页面刷新，而方法(loadUrl )的执行则会使页面刷新。

Android 4.4 后才可使用

仅java代码不同，可以接收JS函数的返回值

public class MainActivity extends Activity {

WebView webView;

Button buttonLeft, buttonRight;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

webView = findViewById(R.id.webview);

buttonLeft = findViewById(R.id.btnLeft);

buttonRight = findViewById(R.id.btnRight);

WebSettings webSettings = webView.getSettings();

//允许使用JS

webSettings.setJavaScriptEnabled(true);

// 设置允许JS弹窗

webSettings.setJavaScriptCanOpenWindowsAutomatically(true);

webView.loadUrl("file:///android_asset/index.html");

buttonLeft.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View view) {

webView.post(new Runnable() {

@Override

public void run() {

webView.evaluateJavascript("javascript:callJS()", new ValueCallback() {

@Override

public void onReceiveValue(String s) {

//将button显示的文字改成JS返回的字符串

buttonLeft.setText(s);

}

});

}

});

}

});

webView.setWebChromeClient(new WebChromeClient() {

@Override

public boolean onJsAlert(WebView view, String url, String message, final JsResult result) {

AlertDialog.Builder b = new AlertDialog.Builder(MainActivity.this);

b.setTitle("alert1");

b.setMessage(message);

b.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {

@Override

public void onClick(DialogInterface dialogInterface, int i) {

result.confirm();

}

});

b.setCancelable(false);

b.create().show();

return true;

}

});

}

}