dwr useLoadingMessage 改进

背景：

遗留项目中用了 dwr 1.1 ，修 bug 看了看 DWRUtil.useLoadingMessage 有问题，修正后再看 dwr 2.0 ,3.0 rc1的 useLoadingMessage 实现，也不是很完美，改进下

dwr:

在 ajax 应用中，在同服务器通信的同时显示当前运行状态，可以达到很好的用户体验，如 经典的 Gmail loading :

dwr 作为整合后端的 ajax 框架，很早的就考虑到了这个问题，提供了useLoadingMessage  ( 底层依靠prehook 与 posthook ) 使得用户可以介入 xhr 请求的发送过程中去，这个机制对所有的请求统一考虑，可以一次设置，每次请求都应用。但是dwr 的实现不是很完美。

dwr 1.1

 

function(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";
    });
}

 

问题：

1.disableZone ie 下百分比大小不能正常设置

2.当多个同时请求发生时，当一个请求返回则 loadingMessage 就被 hidden ，而其实后面的请求还没回来，当前总体状态应为 loading 。

dwr 2.0

 

function(message) {
    var loadingMessage;
    if (message) {
        loadingMessage = message;
    } else {
        loadingMessage = "Loading";
    }
    dwr.engine.setPreHook(function() {
        var disabledZone = dwr.util.byId("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);
            dwr.util._disabledZoneUseCount = 1;
        } else {
            dwr.util.byId("messageZone").innerHTML = loadingMessage;
            disabledZone.style.visibility = "visible";
            dwr.util._disabledZoneUseCount++;
        }
    });
    dwr.engine.setPostHook(function() {
        dwr.util._disabledZoneUseCount--;
        if (dwr.util._disabledZoneUseCount == 0) {
            dwr.util.byId("disabledZone").style.visibility = "hidden";
        }
    });
}

 

新增了一个属性 _disabledZoneUseCount 记录了当前还没处理完毕的请求个数，只有在所有请求处理完毕后才隐藏 loadingMessage 。

问题：

1.disableZone ie 下百分比大小不能正常设置

2.loadingMessage 定位为absolute ，当页面很长出现滚动条时，则当用户在页面底部操作时会出现loadingMessage 仍在文档顶部窗口之外的现象，合适的做法应该是用 fixed 定位，但是 ie6 不支持，但对ie6合适的做法应为 绝对定位到 scrollTop 坐标处即可。

dwr 3.0 rc1 基本等同 dwr 2.0

 

function(message) {
    var loadingMessage;
    if (message) {
        loadingMessage = message;
    } else {
        loadingMessage = "Loading";
    }
    dwr.engine.setPreHook(function() {
        var disabledZone = dwr.util.byId("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%";
            if (window.ActiveXObject) {
                disabledZone.style.background = "white";
                disabledZone.style.filter = "alpha(opacity=0)";
            }
            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";
            document.body.appendChild(messageZone);
            var text = document.createTextNode(loadingMessage);
            messageZone.appendChild(text);
            dwr.util._disabledZoneUseCount = 1;
        } else {
            dwr.util.byId("messageZone").innerHTML = loadingMessage;
            disabledZone.style.visibility = "visible";
            dwr.util._disabledZoneUseCount++;
            dwr.util.byId("messageZone").style.visibility = "visible";
        }
    });
    dwr.engine.setPostHook(function() {
        dwr.util._disabledZoneUseCount--;
        if (dwr.util._disabledZoneUseCount == 0) {
            dwr.util.byId("disabledZone").style.visibility = "hidden";
            dwr.util.byId("messageZone").style.visibility = "hidden";
        }
    });
}

 

我的改进：

可用闭包将当前active的请求封在小作用域内，判断ie6 绝对定位到scrollTop，而对于高级浏览器则直接fixed定位，另外 ie disableZone 百分比大小不起作用，改做每次都算一下，完美解决：

 

(function(){   
    var ua = navigator.userAgent.toLowerCase();
    //judge ie6
    var isIE6=/msie 6/.test(ua);
    
    // number of activeRequests
    var activeRequests=0;
    
    //disable zone
    var disabledZone;
    //loading message zone
    var messageZone
    
    DWRUtil.useLoadingMessage = function(message) {
        var loadingMessage;
        if (message) {
            loadingMessage = message;
        } else {
            loadingMessage = "Loading";
        }
        DWREngine.setPreHook(function() {
            
            var fixTop=(isIE6?(document.documentElement.scrollTop || (document.body.scrollTop || 0)):0)+"px";
            var fixWidth=(document.documentElement.scrollWidth || (document.body.scrollWidth || 0))+"px";
            var fixHeight=(document.documentElement.scrollHeight || (document.body.scrollHeight || 0))+"px";
            
            if (!disabledZone) {
                disabledZone = document.createElement("div");
                disabledZone.setAttribute("id", "disabledZone");
                disabledZone.style.position = "absolute";
                disabledZone.style.zIndex = "10001";
                disabledZone.style.left = "0px";
                disabledZone.style.top = "0px";
                
                //ie 100% can not work
                disabledZone.style.width = fixWidth;
                disabledZone.style.height = fixHeight;
                
                //ie opacity
                if (window.ActiveXObject) {
                    disabledZone.style.background = "#cccccc";
                    disabledZone.style.filter = "alpha(opacity=30)";
                }
                document.body.appendChild(disabledZone);
                messageZone = document.createElement("div");
                messageZone.setAttribute("id", "messageZone");
                if(isIE6) {
                    messageZone.style.position = "absolute";
                } else {
                    messageZone.style.position = "fixed";
                }
                messageZone.style.top = fixTop;
                messageZone.style.right = "0px";
                messageZone.style.background = "red";
                messageZone.style.color = "white";
                messageZone.style.fontFamily = "Arial,Helvetica,sans-serif";
                messageZone.style.padding = "4px";
                document.body.appendChild(messageZone);
                var text = document.createTextNode(loadingMessage);
                messageZone.appendChild(text);
            } else {
                disabledZone.style.width = fixWidth;
                disabledZone.style.height = fixHeight;
                messageZone.style.top = fixTop;
                messageZone.innerHTML = loadingMessage;
                disabledZone.style.visibility = "visible";
                messageZone.style.visibility = "visible";
            }
            ++activeRequests;
        });
        DWREngine.setPostHook(function() {
            --activeRequests;
            if(!activeRequests) {
                disabledZone.style.visibility = "hidden";
                messageZone.style.visibility = "hidden";
            }
        });
    };
    
})();