Using Win32API to realize textbox watermark effect

Demo Effect:

(1) Create a Setwatertext static class
Two references to add:using System.Runtime.InteropServices; Using System.Windows.Forms;

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Runtime.InteropServices;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows.Forms;namespaceWatermark Effect { Public Static classSetwatertext {[DllImport ("user32.dll", CharSet =CharSet.Auto)]Private Static externInt32 SendMessage (IntPtr hWnd,intmsg,intWParam, [MarshalAs (UNMANAGEDTYPE.LPWSTR)]stringLParam); [DllImport ("user32.dll")]        Private Static extern BOOLSendMessage (INTPTR hwnd,intMsgintWParam, StringBuilder lParam); [DllImport ("user32.dll")]        Private Static extern BOOLGetcomboboxinfo (INTPTR hwnd,refcomboboxinfo PCBI); [StructLayout (layoutkind.sequential)]Private structComboboxinfo { Public intcbsize;  PublicRECT RcItem;  PublicRECT Rcbutton;  PublicIntPtr Statebutton;  PublicIntPtr Hwndcombo;  PublicIntPtr Hwnditem;  PublicIntPtr hwndlist; } [StructLayout (layoutkind.sequential)]Private structRECT { Public intLeft ;  Public inttop;  Public intRight ;  Public intBottom; }        Private Const intEm_setcuebanner =0x1501; Private Const intEm_getcuebanner =0x1502;  Public Static voidSetcuetext (Control control,stringtext) {            if(Control isComboBox) {Comboboxinfo Info=Getcomboboxinfo (Control); SendMessage (Info.hwnditem, Em_setcuebanner,0, text); }            Else{SendMessage (control. Handle, Em_setcuebanner,0, text); }        }        Private Staticcomboboxinfo Getcomboboxinfo (Control control) {Comboboxinfo Info=NewComboboxinfo (); //A ComboBox is made up of three controls, a button, a list and textbox; //We want the textboxInfo.cbsize =marshal.sizeof (info); Getcomboboxinfo (Control. Handle,refinfo); returninfo; }         Public Static stringGetcuetext (Control control) {StringBuilder builder=NewStringBuilder (); if(Control isComboBox) {Comboboxinfo Info=NewComboboxinfo (); //A ComboBox is made up of both controls, a list and textbox; //We want the textboxInfo.cbsize =marshal.sizeof (info); Getcomboboxinfo (Control. Handle,refinfo); SendMessage (Info.hwnditem, Em_getcuebanner,0, builder); }            Else{SendMessage (control. Handle, Em_getcuebanner,0, builder); }            returnBuilder.        ToString (); }        //Setwatertext.setcuetext (TextBox1, "FDSADF")    }}

(2) Call can

Private void button1_click (object  sender, EventArgs e)        {            " please fill in User name " );             " please fill in the password " );        }

Using Win32API to realize textbox watermark effect