Question

我有这个C＃代码，我想更改名为label1的标签的文本。当我使用这些函数来检测按下了什么键并从函数中更改label1.Text时，文本不变。如何从此函数中更改label1.Text？

private void Form1_Load(object sender, EventArgs e)
{
    _hookID = SetHook(_proc);
    label1.Font = new Font("Arial", 24, FontStyle.Bold);
}

private static const int WH_KEYBOARD_LL = 13;
private static LowLevelKeyboardProc _proc = HookCallback;
private static IntPtr _hookID = IntPtr.Zero;

private static IntPtr SetHook(LowLevelKeyboardProc proc)
{
    using (Process curProcess = Process.GetCurrentProcess())
    using (ProcessModule curModule = curProcess.MainModule)
    {
        return SetWindowsHookEx(WH_KEYBOARD_LL, proc,
            GetModuleHandle(curModule.ModuleName), 0);
    }
}

private delegate IntPtr LowLevelKeyboardProc(
    int nCode, IntPtr wParam, IntPtr lParam);

private static IntPtr HookCallback(
    int nCode, IntPtr wParam, IntPtr lParam)
{

    if (nCode >= 0 && wParam == (IntPtr)WM_KEYUP)
    {
        int vkCode = Marshal.ReadInt32(lParam);
        Form1 f = new Form1();
        f.label1.Text = "Changed Label"; //<-------------------- change label here
    }

    return CallNextHookEx(_hookID, nCode, wParam, lParam);
}

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr SetWindowsHookEx(int idHook,
    LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode,
    IntPtr wParam, IntPtr lParam);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr GetModuleHandle(string lpModuleName);

Answer 1

你有几个错误：

private static LowLevelKeyboardProc _proc = HookCallback;
private static IntPtr _hookID = IntPtr.Zero;

private static IntPtr HookCallback(

你试图分配一些在静态类方法中运行之前不会存在的东西。那是行不通的;你需要做类似的事情：

private LowLevelKeyboardProc _proc;
private IntPtr _hookID;

private IntPtr HookCallback(...

private void Form1_Load(object sender, EventArgs e)
{
    _proc = new LowLevelKeyboardProc(HookCallback);
    _hookID = SetHook(_proc);

了解static的含义，除非绝对必要，否则不要使用它。它并没有做你认为它做的事情。

下一步：

Form1 f = new Form1();
f.label1.Text = "Changed Label";

您正在创建表单的全新副本f，更改副本中的标签，然后丢弃副本而不显示任何内容或对其执行任何操作。你想要这个：

label1.Text = "Changed Label";

C＃如何更改标签的文本

1 个答案: