我想在 ajaxToolkit:AjaxFileUpload 开始上传时显示一条消息，有没有办法做到这一点

我想在 ajaxToolkit:AjaxFileUpload 开始上传时收到一条消息，有没有办法做到这一点

默认情况下AjaxFileUpload没有这样的事件。但由于 AjaxControlToolkit 是一个开源库，您可以自己添加它。从此页面下载最新的库源：源代码，找到AjaxFileUpload控件源（/Server/AjaxControlToolkit/AjaxFileUpload文件夹）并将以下代码添加到AjaxFileUpload.cs文件中：

[DefaultValue("")]
[Category("Behavior")]
[ExtenderControlEvent]
[ClientPropertyName("uploadStarted")]
public string OnClientUploadStarted
{
    get
    {
        return (string)(ViewState["OnClientUploadStarted"] ?? string.Empty);
    }
    set
    {
        ViewState["OnClientUploadStarted"] = value;
    }
}

之后，修改AjaxFileUpload.pre.js file:

// insert this code right after the _raiseUploadComplete method
add_uploadStarted: function (handler) {
    this.get_events().addHandler("uploadStarted", handler);
},

remove_uploadStarted: function (handler) {
    this.get_events().removeHandler("uploadStarted", handler);
},

_raiseUploadStarted: function () {
    var eh = this.get_events().getHandler("uploadStarted");
    if (eh) {
        eh(this, Sys.EventArgs.Empty);
    }
},

// modify the _doUpload method
_doUpload: function () {

    if (!this._filesInQueue.length || this._filesInQueue.length < 1)
        return;

    this._raiseUploadStarted();

    this._currentQueueIndex = -1;
    if (!this._isFileApiSupports)
        this._createIframe();

    this._processNextFile();
}

然后构建解决方案并享受新功能。