用dwr技术展示页面数据加载状态

用dwr技术显示页面数据加载状态

问题:
用dwr技术查询海量数据时,用户点击按钮,提交请求后,页面长时间没反应.问题反映到我这.当然除了要提高性能外,也得给用户一个提示,比如出现"正在加载数据.."的提示.
解决办法:
如果要实现这种效果,就得在客户端用js判断加载情况，请求前是一种状态,请求后(后台处理,返回数据给前台)又是一种状态.

dwr工具包提供了两个函数,专门处理这两种情况:
(1) 请求前处理
DWREngine.setPreHook(jsfun)
在DWR调用之前设置执行一个函数(但是这个函数无参数),例如显示"正在加载数据.."信息
(2)请求后处理
DWREngine.setPostHook(jsfun) 在DWR调用之后要执行的函数.例如隐藏"正在加载数据.."信息

DWREngine.setPreHook(jsfun)在调用DWR之前，运行jsfun函数。DWREngine.setPostHook(jsfun)在调用完DWR后，运行jsfun函数。
当然我们可以用它来显示程序运行时的动画效果.

function useLoadingMessage(message) { 
  var loadingMessage; 
  if (message) loadingMessage = message; 
  else loadingMessage = "Loading"; 

  DWREngine.setPreHook(function() { 
    var disabledZone = $('disabledZone'); 
    if (!disabledZone) { 
      disabledZone = document.createElement('div'); 
      disabledZone.setAttribute('id', 'disabledZone'); 
      disabledZone.style.position = "absolute"; 
      disabledZone.style.zIndex = "1000"; 
      disabledZone.style.left = "0px"; 
      disabledZone.style.top = "0px"; 
      disabledZone.style.width = "100%"; 
      disabledZone.style.height = "100%"; 
      document.body.appendChild(disabledZone); 
      var messageZone = document.createElement('div'); 
      messageZone.setAttribute('id', 'messageZone'); 
      messageZone.style.position = "absolute"; 
      messageZone.style.top = "0px"; 
      messageZone.style.right = "0px"; 
      messageZone.style.background = "red"; 
      messageZone.style.color = "white"; 
      messageZone.style.fontFamily = "Arial,Helvetica,sans-serif"; 
      messageZone.style.padding = "4px"; 
      disabledZone.appendChild(messageZone); 
      var text = document.createTextNode(loadingMessage); 
      messageZone.appendChild(text); 
    } 
    else { 
      $('messageZone').innerHTML = loadingMessage; 
      disabledZone.style.visibility = 'visible'; 
    } 
  }); 

  DWREngine.setPostHook(function() { 
    $('disabledZone').style.visibility = 'hidden'; 
  }); 
} 

 

function useLoadingImage(imageSrc) { 
  var loadingImage; 
  if (imageSrc) loadingImage = imageSrc; 
  else loadingImage = "ajax-loader.gif"; 
  DWREngine.setPreHook(function() { 
    var disabledImageZone = $('disabledImageZone'); 
    if (!disabledImageZone) { 
      disabledImageZone = document.createElement('div'); 
      disabledImageZone.setAttribute('id', 'disabledImageZone'); 
      disabledImageZone.style.position = "absolute"; 
      disabledImageZone.style.zIndex = "1000"; 
      disabledImageZone.style.left = "0px"; 
      disabledImageZone.style.top = "0px"; 
      disabledImageZone.style.width = "100%"; 
      disabledImageZone.style.height = "100%"; 
      var imageZone = document.createElement('img'); 
      imageZone.setAttribute('id','imageZone'); 
      imageZone.setAttribute('src',imageSrc); 
      imageZone.style.position = "absolute"; 
      imageZone.style.top = "0px"; 
      imageZone.style.right = "0px"; 
      disabledImageZone.appendChild(imageZone); 
      document.body.appendChild(disabledImageZone); 
    } 
    else { 
      $('imageZone').src = imageSrc; 
      disabledImageZone.style.visibility = 'visible'; 
    } 
  }); 
  DWREngine.setPostHook(function() { 
    $('disabledImageZone').style.visibility = 'hidden'; 
  }); 
}