// 按返回键的时候返回上一页面不退出,goBack()表示返回webView的上一页面    public boolean onKeyDown(int keyCoder, KeyEvent event) {        if(!webView1.canGoBack() ){               exit();                  return false;        }        if ( keyCoder == KeyEvent.KEYCODE_BACK) {            webView1.goBack();               exit();              return false;        }        else{             return super.onKeyDown(keyCoder, event);          }    }    public void exit(){          if (!isExit) {              isExit = true;              Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();              mesHandler.sendEmptyMessageDelayed(0, 2000);          } else {              Intent intent = new Intent(Intent.ACTION_MAIN);              intent.addCategory(Intent.CATEGORY_HOME);              startActivity(intent);              System.exit(0);          }      }