function InputQuery(const ACaption, APrompt: string; var Value: string): Boolean; 
InputQuery返回值为是否点了OK 输入的字符串放在了变量Value中

function InputBox(const ACaption, APrompt, ADefault: string): string; 
inputBox返回值是字符串,也就是输入的字符串

procedure TForm1.Button1Click(Sender: TObject);
var
s:string;
begin
//点击了OK按钮后，则
if InputQuery('标题','提示字符',s) then
begin
if s<>'' then //如果输入不为空则
   showmessage(s);
end;

end;

procedure TForm1.Button2Click(Sender: TObject);
var
s:string;
begin
s:=InputBox('标题','提示字符',s);
if s<>'' then
showmessage(s);
end;

首先自定义一个消息ID

const
InputBoxMessage = WM_USER + 200;

接着声明并实现该消息的处理过程

procedure InputBoxSetPasswordChar(var Msg: TMessage); message InputBoxMessage;//声明

procedure Tfrm.InputBoxSetPasswordChar(var Msg: TMessage);//实现
var
hInputForm, hEdit, hButton: HWND;
begin
hInputForm := Screen.Forms[0].Handle;
if (hInputForm <> 0) then
begin
    hEdit := FindWindowEx(hInputForm, 0, 'TEdit', nil);
    SendMessage(hEdit, EM_SETPASSWORDCHAR, Ord('*'), 0);
      // Change button text:
    hButton := FindWindowEx(hInputForm, 0, 'TButton', 'Cancel');
    SendMessage(hButton, WM_SETTEXT,0, Integer(PChar('取消')));
    hButton := FindWindowEx(hInputForm, 0, 'TButton', 'OK');
    SendMessage(hButton, WM_SETTEXT,0, Integer(PChar('确定')));
end; 
end;

使用自定义后的InputBox

PostMessage(Handle, InputBoxMessage, 0, 0);
InputBox('请设置解锁密码','请设置解锁密码（不能为空）：','');