要注入键盘输入，首先需要创建一个**InputInjector class。它表示发送输入数据的虚拟输入设备。然后需要创建一个包含键输入的InjectedInputKeyboardInfo Class**。之后，可以调用inputInjector.InjectKeyboardInput方法来注入键盘输入。
另请注意，Windows.UI.Input.Preview.Injection Namespace中的API需要inputInjectionBrokered受限功能。
下面是您可以参考的代码：

InputInjector inputInjector = InputInjector.TryCreate();

            var controlkey = new InjectedInputKeyboardInfo();
            controlkey.VirtualKey = (ushort)(VirtualKey.LeftControl);
            controlkey.KeyOptions = InjectedInputKeyOptions.None;

            var altkey = new InjectedInputKeyboardInfo();
            altkey.VirtualKey = (ushort)(VirtualKey.Menu);
            altkey.KeyOptions = InjectedInputKeyOptions.None;

            var delkey = new InjectedInputKeyboardInfo();
            delkey.VirtualKey = (ushort)(VirtualKey.Delete);
            delkey.KeyOptions = InjectedInputKeyOptions.None;

            inputInjector.InjectKeyboardInput(new[] { controlkey, altkey, delkey });

            controlkey.KeyOptions = InjectedInputKeyOptions.KeyUp;
            altkey.KeyOptions = InjectedInputKeyOptions.KeyUp;
            delkey.KeyOptions = InjectedInputKeyOptions.KeyUp;

            inputInjector.InjectKeyboardInput(new[] { controlkey, altkey, delkey });