Explore the potential of ListBox (1): automatically adjust the horizontal scroll bar width

After posting the article "two effects of Self-painted ListBox", from the feedback, we still agree with this kind of tips. Next, I will continue to write a series of articles around ListBox to further explore the potential of ListBox, including automatic adjustment of horizontal scroll bar width, real-time tip (TIPS), drag-and-drop insertion tips, etc, create a ListBox group in the rolling area at the end.

Auto adjust horizontal scroll bar width

You can find a lot of articles on the Internet that let ListBox generate a horizontal scroll bar. The method is basically the same. It is to define a function, traverse items to obtain the maximum textwidth value, and then send a message to lb_sethorizontalextent to generate a horizontal scroll bar. A typical example is as follows:

ProcedureSetwidth (Sender: tobject ); VaR I, W: integer; Begin W: = 0; WithListbox1Do begin ForI: = 0ToItems. Count-1Do begin IfCanvas. textwidth (items [I])> WThen W: = canvas. textwidth (items [I]); End; Sendmessage (handle, lb_sethorizontalextent, W + 4, 0 );  End; End;

The above code is indeed available and widely used, but it has a major drawback: high efficiency. Every time you append, insert, or delete an entry in ListBox, you must call this function to recalculate the width of the horizontal scroll bar. It is very time-consuming to traverse all projects and call textwidth. If you drag an entry from the current ListBox to another ListBox, you must recalculate the width of the horizontal scroll bar for two listboxes in one operation. When there are hundreds of entries in the ListBox, you will obviously feel slow.
OK. Now let's change your mind.
When appending or inserting a new entry, you only need to determine whether the textwidth of the new content is greater than the scroll bar width. If it is to adjust the scroll bar width, you can. What about deletion? Yes, traversal is inevitable, but it is not required for each deletion. You can define the index of the entry with the maximum textwidth value in The ListBox variable record. Only the entry needs to be traversed when it is deleted, but it can be ignored in other cases.
In another case, the user may change the screen font, and the width of the horizontal scroll bar must be recalculated. Calculate the new textwidth value of the original maximum entry just like the delete operation.
If there are multiple listboxes on the form, it is also very troublesome to record the maximum entries of each ListBox, So I encapsulate it. The complete code is given below:

UnitKktlistbox; {===================================================== ====================================== Design by: Peng Guohui Date: 2004-12-24 Site: http://kacarton.yeah.net/ Blog: http://blog.csdn.net/nhconch Email: kacarton # sohu.com The article is original to the author. Please contact me before reprinting. for reprinting, please indicate the source of the article and retain the author information. Thank you for your support! ========================================================== =====================================} Interface Uses Windows, messages, sysutils, classes, controls, stdctrls, commctrl; Type Tkktlistbox =Class(Tlistbox) Private Maxlenitemindex: integer; Fscrollwidth: integer; ProcedureLbaddstring (VaR message: Tmessage );MessageLb_addstring; ProcedureLbinsertstring (VaR message: Tmessage );MessageLb_insertstring; ProcedureLbdeletestring (VaR message: Tmessage );MessageLb_deletestring; ProcedureCmfontchanged (VaR message: Tmessage );MessageCm_fontchanged; ProcedureAdjuctscrollwidth (Message: Tmessage ); ProcedureResetscrollwidth; Protected Public ConstructorCreate (aowner: tcomponent );Override; ProcedureCreatewnd;Override; End; Procedure Register; Implementation {Tkktlistbox} ConstructorTkktlistbox. Create (aowner: tcomponent ); Begin InheritedCreate (aowner ); Maxlenitemindex: =-1; Fscrollwidth: = 0; End; ProcedureTkktlistbox. createwnd; Begin InheritedCreatewnd; Canvas. Font: = font; End; ProcedureTkktlistbox. lbaddstring (VaR message: Tmessage ); Begin Inherited; IfMessage. Result = lb_errThenExit; Adjuctscrollwidth (Message ); End; ProcedureTkktlistbox. lbinsertstring (VaR message: Tmessage ); Begin Inherited; IfMessage. Result = lb_errThenExit; IfMessage. wparam <= maxlenitemindexThenMaxlenitemindex: = maxlenitemindex + 1; Adjuctscrollwidth (Message ); End; ProcedureTkktlistbox. lbdeletestring (VaR message: Tmessage ); Begin Inherited; IfMessage. Result = lb_errThenExit; IfMessage. wparam = maxlenitemindexThenResetscrollwidth; End; ProcedureTkktlistbox. cmfontchanged (VaR message: Tmessage ); VaR SZ: size; Begin Inherited; IfMaxlenitemindex =-1ThenExit; // Textwidth is not used here, but the gettextextentpoint32 function is used. If you are interested // You can trace a textwidth function, which is implemented by calling gettextextentpoint32. Gettextextentpoint32 (canvas. Handle, pchar (items [maxlenitemindex]), length (items [maxlenitemindex]), SZ ); Fscrollwidth: = Sz. cx + 4; Perform (lb_sethorizontalextent, fscrollwidth, 0 ); End; ProcedureTkktlistbox. adjuctscrollwidth (Message: Tmessage ); VaR SZ: size; Begin Gettextextentpoint32 (canvas. Handle, pchar (message. lparam), strlen (pchar (message. lparam), SZ ); IfSZ. cx + 4> fscrollwidthThen Begin Fscrollwidth: = Sz. cx + 4; Perform (lb_sethorizontalextent, fscrollwidth, 0 ); Maxlenitemindex: = message. result; End; End; ProcedureTkktlistbox. resetscrollwidth; VaR I, maxwidth: integer; SZ: size; Begin Maxwidth: = 0; I: = items. Count-1; Maxlenitemindex: =-1; WhileI> = 0Do begin SZ. CX: = 0; Gettextextentpoint32 (canvas. Handle, pchar (items [I]), length (items [I]), SZ ); IfSZ. cx + 4> maxwidthThen begin Maxwidth: = Sz. cx + 4; Maxlenitemindex: = I; End; Dec (I ); End; Fscrollwidth: = maxwidth; Perform (lb_sethorizontalextent, fscrollwidth, 0 ); End; Procedure Register; Begin Registercomponents ('kacarton ', [tkktlistbox]); End; End.