WinForm a custom control in a class textbox in a program, adding a feature that loses focus

Principle:

One, in the background code of the control, add the property of the Boolean type CanFocus

Second, in the control's constructor, register the handling method of the Enter event. And in the processing method, depending on the value of the CanFocus property, determines whether the focus can be lost, and if so, calls the sending class of the Windows message.

Third, in the processing method, call the User32.dll class library, send the window message.

Example code:

How Windows messages are sent

WMMessageHepler.cs

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Runtime.InteropServices;usingSystem.Windows.Forms;namespaceyxt.common{ Public classWmmessagehepler {Private Const intWm_killfocus =0x0008; //Send a window message with lost focus         Public Static voidsendblurmsg (IntPtr hwnd) {PostMessage (hwnd, Wm_killfocus,0,0); } [DllImport ("user32.dll")]        Private Static extern voidPostMessage (IntPtr hWnd,intMsgintWParam,intLParam); [DllImport ("User32.dll", EntryPoint ="SendMessage")]        Private Static extern intSendMessage (IntPtr hWnd,intMSG, IntPtr WParam,stringLParam); }}

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Key code for custom controls

WatermarkTextBox.cs

usingSystem;usingSystem.Collections.Generic;usingSystem.Drawing;usingSystem.Linq;usingSystem.Text;usingSystem.Windows.Forms;usingYxt.common;namespaceYxt. client.controls{[ToolboxBitmap (typeof(TextBox))]  Public classWatermarktextbox:textbox { PublicWatermarktextbox () { This. BorderStyle =BorderStyle.FixedSingle;  This. Enter + =NewEventHandler (Watermarktextbox_enter); }        voidWatermarktextbox_enter (Objectsender, EventArgs e) {            if( This. Setblur) { This.            OnBlur (); }        }        PrivateColor _bordercolor =color.red; Private string_watermarktitle; PrivateColor _watermarkcolor =Color.darkgray; Private BOOL_setblur =false; /// <summary>        ///whether the control loses focus/// </summary>         Public BOOLSetblur {Get{return  This. _setblur;} Set            {                 This. _setblur =value;            Invalidate (); }        }        /// <summary>        ///Watermark Font Hint/// </summary>         Public stringWatermarktitle {Get{return_watermarktitle;} Set{_watermarktitle=value;            Invalidate (); }        }        /// <summary>        ///Border Color/// </summary>         PublicColor bordercolor {Get{return_bordercolor;} Set{_bordercolor=value;            Invalidate (); }        }        /// <summary>        ///Watermark Color/// </summary>         PublicColor Watermarkcolor {Get{return_watermarkcolor;} Set{_watermarkcolor=value;            Invalidate (); }        }        Private voidOnBlur () {wmmessagehepler.sendblurmsg ( This.        Handle); }        protected Override voidWndProc (refMessage m) {            Base. WndProc (refm); if(M.msg = =0xf|| M.msg = =0x14|| M.msg = =0x85)            {                if( This. BorderStyle = =borderstyle.fixedsingle) {using(Graphics g = Graphics.fromhwnd ( This. Handle)) {using(varPen =NewPen (_bordercolor)) {G.drawrectangle (pen,0,0, This. Width-1, This. Height-1); Wmpaint (refm); }                    }                }            }        }        Private voidWmpaint (refMessage m) {            using(Graphics graphics = Graphics.fromhwnd (Base. Handle)) {if(Text.length = =0&&!string. IsNullOrEmpty (_watermarktitle)&&!Focused) {textformatflags format=textformatflags.endellipsis|Textformatflags.verticalcenter; if(RightToLeft = =righttoleft.yes) {format|= Textformatflags.righttoleft |Textformatflags.right;                        } textrenderer.drawtext (Graphics, _watermarktitle, Font,Base.                ClientRectangle, _watermarkcolor, format); }            }        }    }}

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Using the example

Method Use Example

Controlsedintor (stringcontrolsname) {            //modifying styles when editing a control            foreach(varValueinch  This. Controls) {varTextBox = value asWatermarktextbox; if(Controlsname = ="Edit")                {                    if(TextBox! =NULL) {Textbox.borderstyle=BorderStyle.FixedSingle; Textbox.readonly=false; Textbox.setblur=false; }                }                Else                {                    if(TextBox! =NULL) {Textbox.borderstyle=BorderStyle.None; Textbox.readonly=true; Textbox.setblur=true; }                }            }        }

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WinForm a custom control in a class textbox in a program, adding a feature that loses focus