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This article mainly introduces "what is the ASP.NET transmission mechanism". In the daily operation, I believe many people have doubts about what the ASP.NET transmission mechanism is. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about "what is the ASP.NET transmission mechanism?" Next, please follow the editor to study!

If the ASP.NET page is requested to the server through post, the framework will follow the event cycle to generate and invoke the control, while the control (if backhaul is supported) will load the backhaul data and map to the control's server-side events, as if replaying the client's behavior (the client presses a button and raises the server-side control's click event). What is the mechanism?

The problem with the transport mechanism designed by the ASP.NET component: if a control needs to handle postback events, it must implement a specific interface IPostBackEventHandler interface:

Public interface IPostBackEventHandler {void RaisePostBackEvent (string eventArgument);}

Another interface for the transport mechanism designed by the ASP.NET component:

IPostBackDataHandler {bool LoadPostData (string postDataKey, NameValueCollection postCollection); void RaisePostDataChangedEvent ();}

Once the control implements these interfaces, the page framework automatically invokes the control's interface IPostBackDataHandler after the PostBack data is complete. LoadPostData, which allows the control to read the data on the post. PostDataKey is the named key name in the PostBack data, and the value passed to the control by the page frame can be obtained through NameValueCollection [postDataKey]. The control should read this value and update its internal state to reflect the state change. If the control returns true, it indicates that the state of the server control has changed, and the page frame immediately calls the RaisePostDataChangedEvent method of the control. At this point, the control should define itself to raise events that are provided by the server control. These events are often the code stage carefully designed by control programmers for aspx programmers who use this key.

As for the other interface, IPostBackEventHandler, it is also the interface called by the server when it is returned. We know that every control has a UniqueID, and when the client triggers a client event that can cause a postback (such as pressing the submit button), then the natural HTTP Post data is sent to the server, and when the server page framework carries out PostBack processing, it will retrieve whether the control supports the IpostBackEventHandler interface, and call the RaisePostBackEvent method of this interface immediately when looking for the UniqueID discovery support of the control. Indicates that an event occurred in the control of the UniqueID that needs to be captured. Obviously, not all events on the client side can be projected to the server, only events and controls that can raise Post Back (that is, events that can submit form data to the server). Note that there is a strict requirement that the UniqueID must correspond to each other on the server side and the client side, otherwise events cannot be mapped.

It is worth noting that if you want to implement an interface, you need to implement the interface as follows, rather than the usual interface method with the same name:

Void IPostBackEventHandler.RaisePostBackEvent (string eventArgument) {. }

The implementation interface of the transport mechanism designed by the ASP.NET component, that is to say, the interface is implemented for the page framework and is also called by the page framework.

On the other hand, on the client side, there are actually only two HTML elements < inoput type=submit > and < input type=image that can cause a backhaul, but other client events can also cause data to be sent back to the server through client script. The Page class provides a series of methods to help implement other ways to trigger a backhaul:

Public string GetPostBackClientEvent (Control control, string argument)

Gets a reference to a client script function that, when called, causes the server to post back to the form.

Public string GetPostBackClientHyperlink (Control control, string argument)

Append _ javascript: to the beginning of the return from the GetPostBackEventReference call so that hyperlink postback processing can occur on the server.

Public string GetPostBackEventReference (Control); public string GetPostBackEventReference (Control, string)

Gets a reference to a client script function that will cause the server

If a control determines that the client raises a postback event through the above method, the control reference page will cause the script to be included in the HTML that is eventually output to the client, and the following implicit variables are hidden in the script:

< input type= "hidden" name= "_ EVENTTARGET" value= "> < input type=" hidden "name=" _ EVENTARGUMENT "value=" > < script language= "javascript" > < / script >

Any client script can be returned to the server as long as it legally calls the _ _ doPostBack method, and the server knows which UniqueID control event was raised.

At this point, the study of "what is the ASP.NET transmission mechanism" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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