Why does ASP NET webforms need the Runat Server attribute

Question

Why do I have to specify runat  server  on all my ASP NET controls when it is a mandatory attribute and server is the only option available in my limited knowledge of ASP NET  and I get an error if I don t use it   I do understand that I can optionally use it on my HTML tags  and I do understand the client server paradigm and what it is actually specifying   Is it a redundant tag that could just be implied by the control being an ASP NET control  or is there an underlying reason

User · Answer

It s there because all controls in ASP  NET inherit from System Web UI Control which has the  runat  attribute   in the class System Web UI HTMLControl  the attribute is not required  however  in the class System Web UI WebControl the attribute is required   edit  let me be more specific   since asp net is pretty much an abstract of HTML  the compiler needs some sort of directive so that it knows that specific tag needs to run server-side  if that attribute wasn t there then is wouldn t know to process it on the server first  if it isn t there it assumes it is regular markup and passes it to the client

User · Answer

Not all controls that can be included in a page must be run at the server   For example    lt INPUT type  submit  runat server   gt   This is essentially the same as    lt asp Button runat server   gt   Remove the runat server tag from the first one and you have a standard HTML button that runs in the browser   There are reasons for and against running a particular control at the server  and there is no way for ASP NET to  assume  what you want based on the HTML markup you include   It might be possible to  infer  the runat server for the  lt asp XXX   gt  family of controls  but my guess is that Microsoft would consider that a hack to the markup syntax and ASP NET engine

User · Answer

Not all controls that can be included in a page must be run at the server   For example    lt INPUT type  submit  runat server   gt   This is essentially the same as    lt asp Button runat server   gt   Remove the runat server tag from the first one and you have a standard HTML button that runs in the browser   There are reasons for and against running a particular control at the server  and there is no way for ASP NET to  assume  what you want based on the HTML markup you include   It might be possible to  infer  the runat server for the  lt asp XXX   gt  family of controls  but my guess is that Microsoft would consider that a hack to the markup syntax and ASP NET engine

User · Answer

Any tag with runat server is added as server control in Page and any html content between is handled as LiteralControls which are also added to Page controls collection

User · Answer

HTML elements in ASP NET files are  by default  treated as text  To make these elements programmable  add a runat  server  attribute to the HTML element  This attribute indicates that the element should be treated as a server control

User · Answer

It s there because all controls in ASP  NET inherit from System Web UI Control which has the  runat  attribute   in the class System Web UI HTMLControl  the attribute is not required  however  in the class System Web UI WebControl the attribute is required   edit  let me be more specific   since asp net is pretty much an abstract of HTML  the compiler needs some sort of directive so that it knows that specific tag needs to run server-side  if that attribute wasn t there then is wouldn t know to process it on the server first  if it isn t there it assumes it is regular markup and passes it to the client

User · Answer

When submitting the data to ASP NET Web server the controls mentioned as Runat      server    will  be represented as Dot Net objects in Server Application  You can manually type the code in HTML controls or else can use Run As Server option by right clicking in design view  ASP NET controls will automatically get this attribute once you drag it from toolbox where usually HTML controls don t

User · Answer

My suspicion is that it has to do with how server-side controls are identified during processing   Rather than having to check every control at runtime by name to determine whether server-side processing needs to be done  it does a selection on the internal node representation by tag   The compiler checks to make sure that all controls that require server tags have them during the validation step

User · Answer

runat  Server  indicates a postback to the server will occur for the HTML  control    Web Forms use postback constantly to signal the server to process a page control event    NET MVC pages DO NOT use postback  except for a form  submit     MVC relies on JQUERY to manage the page on the client side  thus bypassing the need for a lot of postback messages to the server    So   NET Web Forms    use  runat  attribute a lot in the page markup    NET MVC hardly ever uses  runat  attribute in the page markup   Hope this helps clarify why runat is necessary

User · Answer

Pretty redundant attribute  considering the  asp  tag is obviously an ASP element and should be enough to identify it as a server side accessible element   Elsewhere however it used to elevate normal tags to be used in the code-behind

User · Answer

Any tag with runat server is added as server control in Page and any html content between is handled as LiteralControls which are also added to Page controls collection

User · Answer

My suspicion is that it has to do with how server-side controls are identified during processing   Rather than having to check every control at runtime by name to determine whether server-side processing needs to be done  it does a selection on the internal node representation by tag   The compiler checks to make sure that all controls that require server tags have them during the validation step

User · Answer

Not all controls that can be included in a page must be run at the server   For example    lt INPUT type  submit  runat server   gt   This is essentially the same as    lt asp Button runat server   gt   Remove the runat server tag from the first one and you have a standard HTML button that runs in the browser   There are reasons for and against running a particular control at the server  and there is no way for ASP NET to  assume  what you want based on the HTML markup you include   It might be possible to  infer  the runat server for the  lt asp XXX   gt  family of controls  but my guess is that Microsoft would consider that a hack to the markup syntax and ASP NET engine

User · Answer

My suspicion is that it has to do with how server-side controls are identified during processing   Rather than having to check every control at runtime by name to determine whether server-side processing needs to be done  it does a selection on the internal node representation by tag   The compiler checks to make sure that all controls that require server tags have them during the validation step

User · Answer

I usually don t like to guess  but I m going to on this one     If you remember Microsoft s  NET marketing hype back in the day  2001    it was hard to tell what  NET even was  Was it a server  a programming platform  a language  something new entirely  Given the ads  it was ambiguously anything you wanted it to be - it just solved any problem you might have   So  my guess is there was a hidden grand vision that ASP NET code could run anywhere - server side OR client side  in a copy of Internet Explorer tied to the  NET runtime  runat  server  is just a vestigial remnant  left behind because it s client-side equivalent never made it to production   Remember those weird ads     Related  Article from The Register with some  NET history

User · Answer

It s there because all controls in ASP  NET inherit from System Web UI Control which has the  runat  attribute   in the class System Web UI HTMLControl  the attribute is not required  however  in the class System Web UI WebControl the attribute is required   edit  let me be more specific   since asp net is pretty much an abstract of HTML  the compiler needs some sort of directive so that it knows that specific tag needs to run server-side  if that attribute wasn t there then is wouldn t know to process it on the server first  if it isn t there it assumes it is regular markup and passes it to the client

User · Answer

Pretty redundant attribute  considering the  asp  tag is obviously an ASP element and should be enough to identify it as a server side accessible element   Elsewhere however it used to elevate normal tags to be used in the code-behind

User · Answer

I usually don t like to guess  but I m going to on this one     If you remember Microsoft s  NET marketing hype back in the day  2001    it was hard to tell what  NET even was  Was it a server  a programming platform  a language  something new entirely  Given the ads  it was ambiguously anything you wanted it to be - it just solved any problem you might have   So  my guess is there was a hidden grand vision that ASP NET code could run anywhere - server side OR client side  in a copy of Internet Explorer tied to the  NET runtime  runat  server  is just a vestigial remnant  left behind because it s client-side equivalent never made it to production   Remember those weird ads     Related  Article from The Register with some  NET history

User · Answer

I ve always believed it was there more for the understanding that you can mix ASP NET tags and HTML Tags  and HTML Tags have the option of either being runat  server  or not   It doesn t hurt anything to leave the tag in  and it causes a compiler error to take it out   The more things you imply about web language  the less easy it is for a budding programmer to come in and learn it   That s as good a reason as any to be verbose about tag attributes   This conversation was had on Mike Schinkel s Blog between himself and Talbot Crowell of Microsoft National Services   The relevant information is below  first paragraph paraphrased due to grammatical errors in source             but the importance of  lt runat  server  gt  is more for consistency and extensibility        If the developer has to mark some tags  viz   lt asp    gt   for the ASP NET Engine to ignore  then there s also the potential issue of namespace collisions among tags and future enhancements  By requiring the  lt runat  server  gt  attribute  this is negated    It continues      If  lt runat client gt  was required for all client-side tags  the parser would need to parse all tags and strip out the  lt runat client gt  part    He continues        Currently    If my guess is correct  the parser   simply ignores all text  tags or no   tags  unless it is a tag with the   runat server attribute or a     lt        prefix or ssi     lt       include            Also  since ASP NET is designed to   allow separation of the web designers    foo aspx  from the web developers    foo aspx vb   the web designers can   use their own web designer tools to   place HTML and client-side JavaScript   without having to know about ASP NET   specific tags or attributes

User · Answer

If you use it on normal html tags  it means that you can programatically manipulate them in event handlers etc  eg change the href or class of an anchor tag on page load    only do that if you have to  because vanilla html tags go faster    As far as user controls and server controls  no  they just wont work without them  without having delved into the innards of the aspx preprocessor  couldn t say exactly why  but would take a guess that for probably good reasons  they just wrote the parser that way  looking for things explicitly marked as  do something      If  JonSkeet is around anywhere  he will probably be able to provide a much better answer

User · Answer

I just came to this conclusion by trial-and-error  runat  server  is needed to access the elements at run-time on server side  Remove them  recompile and watch what happens

User · Answer

When submitting the data to ASP NET Web server the controls mentioned as Runat      server    will  be represented as Dot Net objects in Server Application  You can manually type the code in HTML controls or else can use Run As Server option by right clicking in design view  ASP NET controls will automatically get this attribute once you drag it from toolbox where usually HTML controls don t

User · Answer

I ve always believed it was there more for the understanding that you can mix ASP NET tags and HTML Tags  and HTML Tags have the option of either being runat  server  or not   It doesn t hurt anything to leave the tag in  and it causes a compiler error to take it out   The more things you imply about web language  the less easy it is for a budding programmer to come in and learn it   That s as good a reason as any to be verbose about tag attributes   This conversation was had on Mike Schinkel s Blog between himself and Talbot Crowell of Microsoft National Services   The relevant information is below  first paragraph paraphrased due to grammatical errors in source             but the importance of  lt runat  server  gt  is more for consistency and extensibility        If the developer has to mark some tags  viz   lt asp    gt   for the ASP NET Engine to ignore  then there s also the potential issue of namespace collisions among tags and future enhancements  By requiring the  lt runat  server  gt  attribute  this is negated    It continues      If  lt runat client gt  was required for all client-side tags  the parser would need to parse all tags and strip out the  lt runat client gt  part    He continues        Currently    If my guess is correct  the parser   simply ignores all text  tags or no   tags  unless it is a tag with the   runat server attribute or a     lt        prefix or ssi     lt       include            Also  since ASP NET is designed to   allow separation of the web designers    foo aspx  from the web developers    foo aspx vb   the web designers can   use their own web designer tools to   place HTML and client-side JavaScript   without having to know about ASP NET   specific tags or attributes

User · Answer

I ve always believed it was there more for the understanding that you can mix ASP NET tags and HTML Tags  and HTML Tags have the option of either being runat  server  or not   It doesn t hurt anything to leave the tag in  and it causes a compiler error to take it out   The more things you imply about web language  the less easy it is for a budding programmer to come in and learn it   That s as good a reason as any to be verbose about tag attributes   This conversation was had on Mike Schinkel s Blog between himself and Talbot Crowell of Microsoft National Services   The relevant information is below  first paragraph paraphrased due to grammatical errors in source             but the importance of  lt runat  server  gt  is more for consistency and extensibility        If the developer has to mark some tags  viz   lt asp    gt   for the ASP NET Engine to ignore  then there s also the potential issue of namespace collisions among tags and future enhancements  By requiring the  lt runat  server  gt  attribute  this is negated    It continues      If  lt runat client gt  was required for all client-side tags  the parser would need to parse all tags and strip out the  lt runat client gt  part    He continues        Currently    If my guess is correct  the parser   simply ignores all text  tags or no   tags  unless it is a tag with the   runat server attribute or a     lt        prefix or ssi     lt       include            Also  since ASP NET is designed to   allow separation of the web designers    foo aspx  from the web developers    foo aspx vb   the web designers can   use their own web designer tools to   place HTML and client-side JavaScript   without having to know about ASP NET   specific tags or attributes

User · Answer

My suspicion is that it has to do with how server-side controls are identified during processing   Rather than having to check every control at runtime by name to determine whether server-side processing needs to be done  it does a selection on the internal node representation by tag   The compiler checks to make sure that all controls that require server tags have them during the validation step

User · Answer

Microsoft Msdn article The Forgotten Controls  HTML Server Controls explains use of runat  server  with an example on text box  lt input type  text  gt  by converting it to  lt input type  text  id  Textbox1  runat  server  gt      Doing this will give you programmatic access to the HTML element on   the server before the Web page is created and sent down to the client    The HTML element must contain an id attribute  This attribute serves   as an identity for the element and enables you to program to elements   by their specific IDs  In addition to this attribute  the HTML element   must contain runat  server   This tells the processing server that the    tag is processed on the server and is not to be considered a   traditional HTML element    In short  to enable programmatic access to the HTML element add runat  server  to it

User · Answer

I think that Microsoft can fix this ambiguity by making the compiler add runat attribute before the page is ever compiled  something like the type-erasure thing that java has with the generics  instead of erasing  it could be writing runat server wherever it sees asp  prefix for tags  so the developer would not need to worry about it

User · Answer

I usually don t like to guess  but I m going to on this one     If you remember Microsoft s  NET marketing hype back in the day  2001    it was hard to tell what  NET even was  Was it a server  a programming platform  a language  something new entirely  Given the ads  it was ambiguously anything you wanted it to be - it just solved any problem you might have   So  my guess is there was a hidden grand vision that ASP NET code could run anywhere - server side OR client side  in a copy of Internet Explorer tied to the  NET runtime  runat  server  is just a vestigial remnant  left behind because it s client-side equivalent never made it to production   Remember those weird ads     Related  Article from The Register with some  NET history

User · Answer

If you use it on normal html tags  it means that you can programatically manipulate them in event handlers etc  eg change the href or class of an anchor tag on page load    only do that if you have to  because vanilla html tags go faster    As far as user controls and server controls  no  they just wont work without them  without having delved into the innards of the aspx preprocessor  couldn t say exactly why  but would take a guess that for probably good reasons  they just wrote the parser that way  looking for things explicitly marked as  do something      If  JonSkeet is around anywhere  he will probably be able to provide a much better answer

User · Answer

If you use it on normal html tags  it means that you can programatically manipulate them in event handlers etc  eg change the href or class of an anchor tag on page load    only do that if you have to  because vanilla html tags go faster    As far as user controls and server controls  no  they just wont work without them  without having delved into the innards of the aspx preprocessor  couldn t say exactly why  but would take a guess that for probably good reasons  they just wrote the parser that way  looking for things explicitly marked as  do something      If  JonSkeet is around anywhere  he will probably be able to provide a much better answer

User · Answer

I ve always believed it was there more for the understanding that you can mix ASP NET tags and HTML Tags  and HTML Tags have the option of either being runat  server  or not   It doesn t hurt anything to leave the tag in  and it causes a compiler error to take it out   The more things you imply about web language  the less easy it is for a budding programmer to come in and learn it   That s as good a reason as any to be verbose about tag attributes   This conversation was had on Mike Schinkel s Blog between himself and Talbot Crowell of Microsoft National Services   The relevant information is below  first paragraph paraphrased due to grammatical errors in source             but the importance of  lt runat  server  gt  is more for consistency and extensibility        If the developer has to mark some tags  viz   lt asp    gt   for the ASP NET Engine to ignore  then there s also the potential issue of namespace collisions among tags and future enhancements  By requiring the  lt runat  server  gt  attribute  this is negated    It continues      If  lt runat client gt  was required for all client-side tags  the parser would need to parse all tags and strip out the  lt runat client gt  part    He continues        Currently    If my guess is correct  the parser   simply ignores all text  tags or no   tags  unless it is a tag with the   runat server attribute or a     lt        prefix or ssi     lt       include            Also  since ASP NET is designed to   allow separation of the web designers    foo aspx  from the web developers    foo aspx vb   the web designers can   use their own web designer tools to   place HTML and client-side JavaScript   without having to know about ASP NET   specific tags or attributes

User · Answer

Not all controls that can be included in a page must be run at the server   For example    lt INPUT type  submit  runat server   gt   This is essentially the same as    lt asp Button runat server   gt   Remove the runat server tag from the first one and you have a standard HTML button that runs in the browser   There are reasons for and against running a particular control at the server  and there is no way for ASP NET to  assume  what you want based on the HTML markup you include   It might be possible to  infer  the runat server for the  lt asp XXX   gt  family of controls  but my guess is that Microsoft would consider that a hack to the markup syntax and ASP NET engine

User · Answer

I usually don t like to guess  but I m going to on this one     If you remember Microsoft s  NET marketing hype back in the day  2001    it was hard to tell what  NET even was  Was it a server  a programming platform  a language  something new entirely  Given the ads  it was ambiguously anything you wanted it to be - it just solved any problem you might have   So  my guess is there was a hidden grand vision that ASP NET code could run anywhere - server side OR client side  in a copy of Internet Explorer tied to the  NET runtime  runat  server  is just a vestigial remnant  left behind because it s client-side equivalent never made it to production   Remember those weird ads     Related  Article from The Register with some  NET history

User · Answer

I think that Microsoft can fix this ambiguity by making the compiler add runat attribute before the page is ever compiled  something like the type-erasure thing that java has with the generics  instead of erasing  it could be writing runat server wherever it sees asp  prefix for tags  so the developer would not need to worry about it

User · Answer

If you use it on normal html tags  it means that you can programatically manipulate them in event handlers etc  eg change the href or class of an anchor tag on page load    only do that if you have to  because vanilla html tags go faster    As far as user controls and server controls  no  they just wont work without them  without having delved into the innards of the aspx preprocessor  couldn t say exactly why  but would take a guess that for probably good reasons  they just wrote the parser that way  looking for things explicitly marked as  do something      If  JonSkeet is around anywhere  he will probably be able to provide a much better answer

User · Answer

I just came to this conclusion by trial-and-error  runat  server  is needed to access the elements at run-time on server side  Remove them  recompile and watch what happens

User · Answer

It s there because all controls in ASP  NET inherit from System Web UI Control which has the  runat  attribute   in the class System Web UI HTMLControl  the attribute is not required  however  in the class System Web UI WebControl the attribute is required   edit  let me be more specific   since asp net is pretty much an abstract of HTML  the compiler needs some sort of directive so that it knows that specific tag needs to run server-side  if that attribute wasn t there then is wouldn t know to process it on the server first  if it isn t there it assumes it is regular markup and passes it to the client

User · Answer

runat  Server  indicates a postback to the server will occur for the HTML  control    Web Forms use postback constantly to signal the server to process a page control event    NET MVC pages DO NOT use postback  except for a form  submit     MVC relies on JQUERY to manage the page on the client side  thus bypassing the need for a lot of postback messages to the server    So   NET Web Forms    use  runat  attribute a lot in the page markup    NET MVC hardly ever uses  runat  attribute in the page markup   Hope this helps clarify why runat is necessary

User · Answer

Microsoft Msdn article The Forgotten Controls  HTML Server Controls explains use of runat  server  with an example on text box  lt input type  text  gt  by converting it to  lt input type  text  id  Textbox1  runat  server  gt      Doing this will give you programmatic access to the HTML element on   the server before the Web page is created and sent down to the client    The HTML element must contain an id attribute  This attribute serves   as an identity for the element and enables you to program to elements   by their specific IDs  In addition to this attribute  the HTML element   must contain runat  server   This tells the processing server that the    tag is processed on the server and is not to be considered a   traditional HTML element    In short  to enable programmatic access to the HTML element add runat  server  to it

User · Answer

HTML elements in ASP NET files are  by default  treated as text  To make these elements programmable  add a runat  server  attribute to the HTML element  This attribute indicates that the element should be treated as a server control

[asp.net] Why does ASP.NET webforms need the Runat="Server" attribute?

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