在 .net 2.0 中,有没有一种简单的方法将 MessageBox 居中于父窗体?
在 .net 2.0 中,有没有一种简单的方法将 MessageBox 居中于父窗体?
我在C#中非常需要这个功能,找到了居中MessageBox C#。
下面是一个格式很好的版本
using System;
using System.Windows.Forms;
using System.Text;
using System.Drawing;
using System.Runtime.InteropServices;
public class MessageBoxEx
{
private static IWin32Window _owner;
private static HookProc _hookProc;
private static IntPtr _hHook;
public static DialogResult Show(string text)
{
Initialize();
return MessageBox.Show(text);
}
public static DialogResult Show(string text, string caption)
{
Initialize();
return MessageBox.Show(text, caption);
}
public static DialogResult Show(string text, string caption, MessageBoxButtons buttons)
{
Initialize();
return MessageBox.Show(text, caption, buttons);
}
public static DialogResult Show(string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon)
{
Initialize();
return MessageBox.Show(text, caption, buttons, icon);
}
public static DialogResult Show(string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon, MessageBoxDefaultButton defButton)
{
Initialize();
return MessageBox.Show(text, caption, buttons, icon, defButton);
}
public static DialogResult Show(string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon, MessageBoxDefaultButton defButton, MessageBoxOptions options)
{
Initialize();
return MessageBox.Show(text, caption, buttons, icon, defButton, options);
}
public static DialogResult Show(IWin32Window owner, string text)
{
_owner = owner;
Initialize();
return MessageBox.Show(owner, text);
}
public static DialogResult Show(IWin32Window owner, string text, string caption)
{
_owner = owner;
Initialize();
return MessageBox.Show(owner, text, caption);
}
public static DialogResult Show(IWin32Window owner, string text, string caption, MessageBoxButtons buttons)
{
_owner = owner;
Initialize();
return MessageBox.Show(owner, text, caption, buttons);
}
public static DialogResult Show(IWin32Window owner, string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon)
{
_owner = owner;
Initialize();
return MessageBox.Show(owner, text, caption, buttons, icon);
}
public static DialogResult Show(IWin32Window owner, string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon, MessageBoxDefaultButton defButton)
{
_owner = owner;
Initialize();
return MessageBox.Show(owner, text, caption, buttons, icon, defButton);
}
public static DialogResult Show(IWin32Window owner, string text, string caption, MessageBoxButtons buttons, MessageBoxIcon icon, MessageBoxDefaultButton defButton, MessageBoxOptions options)
{
_owner = owner;
Initialize();
return MessageBox.Show(owner, text, caption, buttons, icon,
defButton, options);
}
public delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);
public delegate void TimerProc(IntPtr hWnd, uint uMsg, UIntPtr nIDEvent, uint dwTime);
public const int WH_CALLWNDPROCRET = 12;
public enum CbtHookAction : int
{
HCBT_MOVESIZE = 0,
HCBT_MINMAX = 1,
HCBT_QS = 2,
HCBT_CREATEWND = 3,
HCBT_DESTROYWND = 4,
HCBT_ACTIVATE = 5,
HCBT_CLICKSKIPPED = 6,
HCBT_KEYSKIPPED = 7,
HCBT_SYSCOMMAND = 8,
HCBT_SETFOCUS = 9
}
[DllImport("user32.dll")]
private static extern bool GetWindowRect(IntPtr hWnd, ref Rectangle lpRect);
[DllImport("user32.dll")]
private static extern int MoveWindow(IntPtr hWnd, int X, int Y, int nWidth, int nHeight, bool bRepaint);
[DllImport("User32.dll")]
public static extern UIntPtr SetTimer(IntPtr hWnd, UIntPtr nIDEvent, uint uElapse, TimerProc lpTimerFunc);
[DllImport("User32.dll")]
public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll")]
public static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);
[DllImport("user32.dll")]
public static extern int UnhookWindowsHookEx(IntPtr idHook);
[DllImport("user32.dll")]
public static extern IntPtr CallNextHookEx(IntPtr idHook, int nCode, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll")]
public static extern int GetWindowTextLength(IntPtr hWnd);
[DllImport("user32.dll")]
public static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int maxLength);
[DllImport("user32.dll")]
public static extern int EndDialog(IntPtr hDlg, IntPtr nResult);
[StructLayout(LayoutKind.Sequential)]
public struct CWPRETSTRUCT
{
public IntPtr lResult;
public IntPtr lParam;
public IntPtr wParam;
public uint message;
public IntPtr hwnd;
} ;
static void MessageBoxEx()
{
_hookProc = new HookProc(MessageBoxHookProc);
_hHook = IntPtr.Zero;
}
private static void Initialize()
{
if (_hHook != IntPtr.Zero)
{
throw new NotSupportedException("multiple calls are not supported");
}
if (_owner != null)
{
_hHook = SetWindowsHookEx(WH_CALLWNDPROCRET, _hookProc, IntPtr.Zero, AppDomain.GetCurrentThreadId());
}
}
private static IntPtr MessageBoxHookProc(int nCode, IntPtr wParam, IntPtr lParam)
{
if (nCode < 0)
{
return CallNextHookEx(_hHook, nCode, wParam, lParam);
}
CWPRETSTRUCT msg = (CWPRETSTRUCT)Marshal.PtrToStructure(lParam, typeof(CWPRETSTRUCT));
IntPtr hook = _hHook;
if (msg.message == (int)CbtHookAction.HCBT_ACTIVATE)
{
try
{
CenterWindow(msg.hwnd);
}
finally
{
UnhookWindowsHookEx(_hHook);
_hHook = IntPtr.Zero;
}
}
return CallNextHookEx(hook, nCode, wParam, lParam);
}
private static void CenterWindow(IntPtr hChildWnd)
{
Rectangle recChild = new Rectangle(0, 0, 0, 0);
bool success = GetWindowRect(hChildWnd, ref recChild);
int width = recChild.Width - recChild.X;
int height = recChild.Height - recChild.Y;
Rectangle recParent = new Rectangle(0, 0, 0, 0);
success = GetWindowRect(_owner.Handle, ref recParent);
Point ptCenter = new Point(0, 0);
ptCenter.X = recParent.X + ((recParent.Width - recParent.X) / 2);
ptCenter.Y = recParent.Y + ((recParent.Height - recParent.Y) / 2);
Point ptStart = new Point(0, 0);
ptStart.X = (ptCenter.X - (width / 2));
ptStart.Y = (ptCenter.Y - (height / 2));
ptStart.X = (ptStart.X < 0) ? 0 : ptStart.X;
ptStart.Y = (ptStart.Y < 0) ? 0 : ptStart.Y;
int result = MoveWindow(hChildWnd, ptStart.X, ptStart.Y, width,
height, false);
}
}
MessageBoxEx.Show(this, "保存前请修正验证错误。", "验证错误");
- JohnBAppDomain.GetCurrentThreadId()
正常工作并抑制警告吗?Thread.CurrentThread.ManagedThreadId
不能做到这一点吗? - conners_owner
声明之前添加以下内容:[DllImport("user32.dll", SetLastError = true)]
...static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);
然后这3行代码将 "替换" AppDomain.GetCurrentThreadId()
的警告: uint processID = 0;
...IntPtr ptr = _owner.Handle;
..._hHook = SetWindowsHookEx(WH_CALLWNDPROCRET, _hookProc, IntPtr.Zero, (int) GetWindowThreadProcessId(ptr, out processID));
抱歉没有换行符,这是我能做到的最好的。 - conners消息框始终居中于屏幕。您可以提供一个所有者,但这只是用于Z顺序,而不是居中。唯一的方法是使用Win32钩子并自己居中。如果搜索在线代码,您就可以找到执行此操作的代码。
更简单的方法是编写您自己的消息框类并添加居中功能。然后,您还可以添加默认标题、不再显示复选框并使它们成为无模式窗口。
“Win32 hooks”可能指的是使用SetWindowsHookEx
,如此示例所示。
但为什么要止步于MessageBox特定的实现?像下面这样使用以下类:
private void OnFormClosing(object sender, FormClosingEventArgs e)
{
DialogResult dg;
using (DialogCenteringService centeringService = new DialogCenteringService(this)) // center message box
{
dg = MessageBox.Show(this, "Are you sure?", "Confirm exit", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
}
if (dg == DialogResult.No)
{
e.Cancel = true;
}
}
您可以在任何显示对话框窗口的地方使用以下代码,即使它们由另一个线程拥有(我们的应用程序具有多个UI线程):
(这里是更新后的代码,它考虑了监视器工作区域,以便对话框不会在两个监视器之间居中或部分超出屏幕。您需要用到下面的enum SetWindowPosFlags
)
public class DialogCenteringService : IDisposable
{
private readonly IWin32Window owner;
private readonly HookProc hookProc;
private readonly IntPtr hHook = IntPtr.Zero;
public DialogCenteringService(IWin32Window owner)
{
if (owner == null) throw new ArgumentNullException("owner");
this.owner = owner;
hookProc = DialogHookProc;
hHook = SetWindowsHookEx(WH_CALLWNDPROCRET, hookProc, IntPtr.Zero, GetCurrentThreadId());
}
private IntPtr DialogHookProc(int nCode, IntPtr wParam, IntPtr lParam)
{
if (nCode < 0)
{
return CallNextHookEx(hHook, nCode, wParam, lParam);
}
CWPRETSTRUCT msg = (CWPRETSTRUCT)Marshal.PtrToStructure(lParam, typeof(CWPRETSTRUCT));
IntPtr hook = hHook;
if (msg.message == (int)CbtHookAction.HCBT_ACTIVATE)
{
try
{
CenterWindow(msg.hwnd);
}
finally
{
UnhookWindowsHookEx(hHook);
}
}
return CallNextHookEx(hook, nCode, wParam, lParam);
}
public void Dispose()
{
UnhookWindowsHookEx(hHook);
}
private void CenterWindow(IntPtr hChildWnd)
{
Rectangle recChild = new Rectangle(0, 0, 0, 0);
bool success = GetWindowRect(hChildWnd, ref recChild);
if (!success)
{
return;
}
int width = recChild.Width - recChild.X;
int height = recChild.Height - recChild.Y;
Rectangle recParent = new Rectangle(0, 0, 0, 0);
success = GetWindowRect(owner.Handle, ref recParent);
if (!success)
{
return;
}
Point ptCenter = new Point(0, 0);
ptCenter.X = recParent.X + ((recParent.Width - recParent.X) / 2);
ptCenter.Y = recParent.Y + ((recParent.Height - recParent.Y) / 2);
Point ptStart = new Point(0, 0);
ptStart.X = (ptCenter.X - (width / 2));
ptStart.Y = (ptCenter.Y - (height / 2));
//MoveWindow(hChildWnd, ptStart.X, ptStart.Y, width, height, false);
Task.Factory.StartNew(() => SetWindowPos(hChildWnd, (IntPtr)0, ptStart.X, ptStart.Y, width, height, SetWindowPosFlags.SWP_ASYNCWINDOWPOS | SetWindowPosFlags.SWP_NOSIZE | SetWindowPosFlags.SWP_NOACTIVATE | SetWindowPosFlags.SWP_NOOWNERZORDER | SetWindowPosFlags.SWP_NOZORDER));
}
// some p/invoke
// ReSharper disable InconsistentNaming
public delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);
public delegate void TimerProc(IntPtr hWnd, uint uMsg, UIntPtr nIDEvent, uint dwTime);
private const int WH_CALLWNDPROCRET = 12;
// ReSharper disable EnumUnderlyingTypeIsInt
private enum CbtHookAction : int
// ReSharper restore EnumUnderlyingTypeIsInt
{
// ReSharper disable UnusedMember.Local
HCBT_MOVESIZE = 0,
HCBT_MINMAX = 1,
HCBT_QS = 2,
HCBT_CREATEWND = 3,
HCBT_DESTROYWND = 4,
HCBT_ACTIVATE = 5,
HCBT_CLICKSKIPPED = 6,
HCBT_KEYSKIPPED = 7,
HCBT_SYSCOMMAND = 8,
HCBT_SETFOCUS = 9
// ReSharper restore UnusedMember.Local
}
[DllImport("kernel32.dll")]
static extern int GetCurrentThreadId();
[DllImport("user32.dll")]
private static extern bool GetWindowRect(IntPtr hWnd, ref Rectangle lpRect);
[DllImport("user32.dll")]
private static extern int MoveWindow(IntPtr hWnd, int X, int Y, int nWidth, int nHeight, bool bRepaint);
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int x, int y, int cx, int cy, SetWindowPosFlags uFlags);
[DllImport("User32.dll")]
public static extern UIntPtr SetTimer(IntPtr hWnd, UIntPtr nIDEvent, uint uElapse, TimerProc lpTimerFunc);
[DllImport("User32.dll")]
public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll")]
public static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);
[DllImport("user32.dll")]
public static extern int UnhookWindowsHookEx(IntPtr idHook);
[DllImport("user32.dll")]
public static extern IntPtr CallNextHookEx(IntPtr idHook, int nCode, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll")]
public static extern int GetWindowTextLength(IntPtr hWnd);
[DllImport("user32.dll")]
public static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int maxLength);
[DllImport("user32.dll")]
public static extern int EndDialog(IntPtr hDlg, IntPtr nResult);
[StructLayout(LayoutKind.Sequential)]
public struct CWPRETSTRUCT
{
public IntPtr lResult;
public IntPtr lParam;
public IntPtr wParam;
public uint message;
public IntPtr hwnd;
};
// ReSharper restore InconsistentNaming
}
[Flags]
public enum SetWindowPosFlags : uint
{
// ReSharper disable InconsistentNaming
/// <summary>
/// If the calling thread and the thread that owns the window are attached to different input queues, the system posts the request to the thread that owns the window. This prevents the calling thread from blocking its execution while other threads process the request.
/// </summary>
SWP_ASYNCWINDOWPOS = 0x4000,
/// <summary>
/// Prevents generation of the WM_SYNCPAINT message.
/// </summary>
SWP_DEFERERASE = 0x2000,
/// <summary>
/// Draws a frame (defined in the window's class description) around the window.
/// </summary>
SWP_DRAWFRAME = 0x0020,
/// <summary>
/// Applies new frame styles set using the SetWindowLong function. Sends a WM_NCCALCSIZE message to the window, even if the window's size is not being changed. If this flag is not specified, WM_NCCALCSIZE is sent only when the window's size is being changed.
/// </summary>
SWP_FRAMECHANGED = 0x0020,
/// <summary>
/// Hides the window.
/// </summary>
SWP_HIDEWINDOW = 0x0080,
/// <summary>
/// Does not activate the window. If this flag is not set, the window is activated and moved to the top of either the topmost or non-topmost group (depending on the setting of the hWndInsertAfter parameter).
/// </summary>
SWP_NOACTIVATE = 0x0010,
/// <summary>
/// Discards the entire contents of the client area. If this flag is not specified, the valid contents of the client area are saved and copied back into the client area after the window is sized or repositioned.
/// </summary>
SWP_NOCOPYBITS = 0x0100,
/// <summary>
/// Retains the current position (ignores X and Y parameters).
/// </summary>
SWP_NOMOVE = 0x0002,
/// <summary>
/// Does not change the owner window's position in the Z order.
/// </summary>
SWP_NOOWNERZORDER = 0x0200,
/// <summary>
/// Does not redraw changes. If this flag is set, no repainting of any kind occurs. This applies to the client area, the nonclient area (including the title bar and scroll bars), and any part of the parent window uncovered as a result of the window being moved. When this flag is set, the application must explicitly invalidate or redraw any parts of the window and parent window that need redrawing.
/// </summary>
SWP_NOREDRAW = 0x0008,
/// <summary>
/// Same as the SWP_NOOWNERZORDER flag.
/// </summary>
SWP_NOREPOSITION = 0x0200,
/// <summary>
/// Prevents the window from receiving the WM_WINDOWPOSCHANGING message.
/// </summary>
SWP_NOSENDCHANGING = 0x0400,
/// <summary>
/// Retains the current size (ignores the cx and cy parameters).
/// </summary>
SWP_NOSIZE = 0x0001,
/// <summary>
/// Retains the current Z order (ignores the hWndInsertAfter parameter).
/// </summary>
SWP_NOZORDER = 0x0004,
/// <summary>
/// Displays the window.
/// </summary>
SWP_SHOWWINDOW = 0x0040,
// ReSharper restore InconsistentNaming
}
Rectangle
和本地的 RECT
导致的。我在 Github 仓库的评论中发布了修复方法。 - Andy我稍微修改了之前的回答,并编写了WPF版本的MessageBoxEx。这段代码对我很好用。如果有问题,请随时通知我。
请注意:
我在构造函数中使用GeneralObjects.MainWindowInstance
来初始化与我的主窗口相关联的类,但实际上我将它用于任何窗口,因为它具有缓存最后一个父窗口的功能。因此,您可以简单地从构造函数中删除所有内容。
public class MessageBoxEx
{
private static HwndSource source_ = null;
private static HwndSourceHook hook_ = null;
static MessageBoxEx()
{
try
{
// create cached
createHwndSource_(GeneralObjects.MainWindowInstance);
hook_ = new HwndSourceHook(HwndSourceHook);
}
finally
{
if (null == source_ ||
null == hook_)
{
source_ = null;
hook_ = null;
}
}
}
private static void createHwndSource_(Window owner)
{
source_ = (HwndSource)PresentationSource.FromVisual(owner);
}
public static void Initialize_(Window owner = null)
{
try
{
if (null != owner)
{
if(source_.RootVisual != owner)
{
createHwndSource_(owner);
}
}
}
finally
{
if (null == source_ ||
null == hook_)
{
source_ = null;
hook_ = null;
}
}
if (null != source_ &&
null != hook_)
{
source_.AddHook(hook_);
}
}
public static MessageBoxResult Show(string messageBoxText)
{
Initialize_();
return System.Windows.MessageBox.Show(messageBoxText);
}
public static MessageBoxResult Show(string messageBoxText, string caption)
{
Initialize_();
return System.Windows.MessageBox.Show(messageBoxText, caption);
}
public static MessageBoxResult Show(Window owner, string messageBoxText)
{
Initialize_(owner);
return System.Windows.MessageBox.Show(owner, messageBoxText);
}
public static MessageBoxResult Show(string messageBoxText, string caption, MessageBoxButton button)
{
Initialize_();
return System.Windows.MessageBox.Show(messageBoxText, caption, button);
}
public static MessageBoxResult Show(Window owner, string messageBoxText, string caption)
{
Initialize_(owner);
return System.Windows.MessageBox.Show(owner, messageBoxText, caption);
}
public static MessageBoxResult Show(string messageBoxText, string caption, MessageBoxButton button, MessageBoxImage icon)
{
Initialize_();
return System.Windows.MessageBox.Show(messageBoxText, caption, button, icon);
}
public static MessageBoxResult Show(Window owner, string messageBoxText, string caption, MessageBoxButton button)
{
Initialize_(owner);
return System.Windows.MessageBox.Show(owner, messageBoxText, caption, button);
}
public static MessageBoxResult Show(string messageBoxText, string caption, MessageBoxButton button, MessageBoxImage icon, MessageBoxResult defaultResult)
{
Initialize_();
return System.Windows.MessageBox.Show(messageBoxText, caption, button, icon, defaultResult);
}
public static MessageBoxResult Show(Window owner, string messageBoxText, string caption, MessageBoxButton button, MessageBoxImage icon)
{
Initialize_(owner);
return System.Windows.MessageBox.Show(owner, messageBoxText, caption, button, icon);
}
public static MessageBoxResult Show(string messageBoxText, string caption, MessageBoxButton button, MessageBoxImage icon, MessageBoxResult defaultResult, System.Windows.MessageBoxOptions options)
{
Initialize_();
return System.Windows.MessageBox.Show(messageBoxText, caption, button, icon, defaultResult, options);
}
public static MessageBoxResult Show(Window owner, string messageBoxText, string caption, MessageBoxButton button, MessageBoxImage icon, MessageBoxResult defaultResult)
{
Initialize_(owner);
return System.Windows.MessageBox.Show(owner, messageBoxText, caption, button, icon, defaultResult);
}
public static MessageBoxResult Show(Window owner, string messageBoxText, string caption, MessageBoxButton button, MessageBoxImage icon, MessageBoxResult defaultResult, System.Windows.MessageBoxOptions options)
{
Initialize_(owner);
return System.Windows.MessageBox.Show(owner, messageBoxText, caption, button, icon, defaultResult, options);
}
private enum WM : int
{
WM_ACTIVATE = 0x0006
}
private static IntPtr HwndSourceHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
if ((int)WM.WM_ACTIVATE == msg &&
source_.Handle == hwnd &&
0 == (int)wParam)
{
try
{
CenterWindow(lParam);
}
finally
{
// remove hook at once after moved message box window.
source_.RemoveHook(hook_);
}
}
return IntPtr.Zero;
}
[DllImport("user32.dll")]
private static extern bool GetWindowRect(IntPtr hWnd, ref Rectangle lpRect);
[DllImport("user32.dll")]
private static extern int MoveWindow(IntPtr hWnd, int X, int Y, int nWidth, int nHeight, bool bRepaint);
private static void CenterWindow(IntPtr hChildWnd)
{
System.Drawing.Rectangle recChild = new System.Drawing.Rectangle(0, 0, 0, 0);
bool success = GetWindowRect(hChildWnd, ref recChild);
int width = recChild.Width - recChild.X;
int height = recChild.Height - recChild.Y;
System.Drawing.Rectangle recParent = new System.Drawing.Rectangle(0, 0, 0, 0);
success = GetWindowRect(source_.Handle, ref recParent);
System.Drawing.Point ptCenter = new System.Drawing.Point(0, 0);
ptCenter.X = recParent.X + ((recParent.Width - recParent.X) / 2);
ptCenter.Y = recParent.Y + ((recParent.Height - recParent.Y) / 2);
System.Drawing.Point ptStart = new System.Drawing.Point(0, 0);
ptStart.X = (ptCenter.X - (width / 2));
ptStart.Y = (ptCenter.Y - (height / 2));
// I have commented this code because of I have 2 monitors
// so If application located at 1st monitor
// message box can appear at second one.
/*
ptStart.X = (ptStart.X < 0) ? 0 : ptStart.X;
ptStart.Y = (ptStart.Y < 0) ? 0 : ptStart.Y;
*/
int result = MoveWindow(hChildWnd, ptStart.X, ptStart.Y, width,
height, false);
}
}
试试这个,它足够简单,可以证明时间的价值...
这是Win32 API写的,用C语言编写。根据需要翻译它...
case WM_NOTIFY:{
HWND X=FindWindow("#32770",NULL);
if(GetParent(X)==H_frame){int Px,Py,Sx,Sy; RECT R1,R2;
GetWindowRect(hwnd,&R1); GetWindowRect(X,&R2);
Sx=R2.right-R2.left,Px=R1.left+(R1.right-R1.left)/2-Sx/2;
Sy=R2.bottom-R2.top,Py=R1.top+(R1.bottom-R1.top)/2-Sy/2;
MoveWindow(X,Px,Py,Sx,Sy,1);
}
} break;
如果使用自己的面板或表单,那么这无疑是最简单的方法,但会增加一些背景(设计师)代码的负担。它可以在不编写所有自定义代码的情况下提供居中和操作的所有控制。