回答編集履歴

  「文字入力支援君」はradianさんの言うようにおそらく、

  1. 対象アプリをアクティブ化

  1. クリップボードに文字をコピー

  1. Ctrl+Vを送る

 

  という動作をしています。

 

  対象アプリがアクティブ化したときにカーソルがない（ボタン等にフォーカスがある）と貼り付けられないので、特に入力エリアを探したりはしていなそうです（特定アプリに特別対応があるかもしれませんが）

 

  最低限動作確認できるサンプルを作りました。

  ##### 使い方

  1. 支援君のようにピンクの四角を対象アプリにドラッグ＆ドロップ

  1. テキストボックスに何か入力

  1. 貼り付けボタンを押す

 

  ##### 注意

  * エラーチェック一切なし

  * Word・Excelは手元にないので未確認

 

  using System;

  using System.Drawing;

  using System.Runtime.InteropServices;

  using System.Text;

  using System.Windows.Forms;

 

  namespace Questions252432

  {

  public partial class Form1 : Form

  {

  private IntPtr hWnd;

 

  public Form1() => InitializeComponent();

 

  private void Panel1_MouseDown(object sender, MouseEventArgs e)

  if(e.Button == MouseButtons.Left) panel1.Capture = true;

 

  private void Panel1_MouseUp(object sender, MouseEventArgs e)

  panel1.Capture = false;

  var p = NativeMethods.GetCursorPos();

  var h = NativeMethods.WindowFromPoint(p);

  hWnd = NativeMethods.GetAncestor(h);

 

  label_title.Text = $"Title: {NativeMethods.GetWindowText(hWnd)}";

  label_class.Text = $"Class: {NativeMethods.GetClassName(hWnd)}";

 

  private void Button1_Click(object sender, EventArgs e)

  Clipboard.SetText(textBox1.Text);

  NativeMethods.SetForegroundWindow(hWnd);

  SendKeys.Send("^v");

 

  private static class NativeMethods

  private static extern bool GetCursorPos(out Point pPoint);

  public static Point GetCursorPos()

  GetCursorPos(out var p);

  return p;

  public static extern IntPtr WindowFromPoint(Point point);

 

  private static extern IntPtr GetAncestor(IntPtr hWnd, uint gaFlags);

  public static IntPtr GetAncestor(IntPtr hWnd) => GetAncestor(hWnd, GA_ROOTOWNER);

  private const uint GA_ROOTOWNER = 3;

 

  [DllImport("user32", CharSet = CharSet.Unicode)]

  private static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

  public static string GetWindowText(IntPtr hWnd)

  var sb = new StringBuilder(100);

  GetWindowText(hWnd, sb, sb.Capacity);

  return sb.ToString();

 

  [DllImport("user32", CharSet = CharSet.Unicode)]

  private static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);

  public static string GetClassName(IntPtr hWnd)

  var sb = new StringBuilder(100);

  GetClassName(hWnd, sb, sb.Capacity);

  return sb.ToString();

  public static extern bool SetForegroundWindow(IntPtr hWnd);

  }

  }

  ```

 

  namespace Questions252432

  {

  partial class Form1

  {

  /// <summary>

  /// 必要なデザイナー変数です。

  /// </summary>

  private System.ComponentModel.IContainer components = null;

 

  /// <summary>

  /// 使用中のリソースをすべてクリーンアップします。

  /// </summary>

  /// <param name="disposing">マネージド リソースを破棄する場合は true を指定し、その他の場合は false を指定します。</param>

  protected override void Dispose(bool disposing)

  if(disposing && (components != null))

  components.Dispose();

  base.Dispose(disposing);

 

  #region Windows フォーム デザイナーで生成されたコード

 

  /// <summary>

  /// デザイナー サポートに必要なメソッドです。このメソッドの内容を

  /// コード エディターで変更しないでください。

  /// </summary>

  private void InitializeComponent()

  this.button1 = new System.Windows.Forms.Button();

  this.label_title = new System.Windows.Forms.Label();

  this.label_class = new System.Windows.Forms.Label();

  this.textBox1 = new System.Windows.Forms.TextBox();

  this.panel1 = new System.Windows.Forms.Panel();

  this.SuspendLayout();

  // button1

  this.button1.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Bottom | System.Windows.Forms.AnchorStyles.Right)));

  this.button1.Location = new System.Drawing.Point(297, 222);

  this.button1.Name = "button1";

  this.button1.Size = new System.Drawing.Size(75, 23);

  this.button1.TabIndex = 0;

  this.button1.Text = "貼り付け";

  this.button1.UseVisualStyleBackColor = true;

  this.button1.Click += new System.EventHandler(this.Button1_Click);

  // label_title

  this.label_title.AutoSize = true;

  this.label_title.Location = new System.Drawing.Point(54, 16);

  this.label_title.Name = "label_title";

  this.label_title.Size = new System.Drawing.Size(30, 12);

  this.label_title.TabIndex = 1;

  this.label_title.Text = "Title:";

  // label_class

  this.label_class.AutoSize = true;

  this.label_class.Location = new System.Drawing.Point(54, 31);

  this.label_class.Name = "label_class";

  this.label_class.Size = new System.Drawing.Size(36, 12);

  this.label_class.TabIndex = 2;

  this.label_class.Text = "Class:";

  // textBox1

  this.textBox1.AcceptsReturn = true;

  this.textBox1.AcceptsTab = true;

  this.textBox1.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom)

  | System.Windows.Forms.AnchorStyles.Left)

  | System.Windows.Forms.AnchorStyles.Right)));

  this.textBox1.Location = new System.Drawing.Point(12, 54);

  this.textBox1.Multiline = true;

  this.textBox1.Name = "textBox1";

  this.textBox1.Size = new System.Drawing.Size(360, 162);

  this.textBox1.TabIndex = 3;

  // panel1

  this.panel1.BackColor = System.Drawing.Color.FromArgb(((int)(((byte)(255)))), ((int)(((byte)(128)))), ((int)(((byte)(128)))));

  this.panel1.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle;

  this.panel1.Cursor = System.Windows.Forms.Cursors.Cross;

  this.panel1.Location = new System.Drawing.Point(12, 12);

  this.panel1.Name = "panel1";

  this.panel1.Size = new System.Drawing.Size(36, 36);

  this.panel1.TabIndex = 4;

  this.panel1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Panel1_MouseDown);

  this.panel1.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Panel1_MouseUp);

  // Form1

  this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);

  this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;

  this.ClientSize = new System.Drawing.Size(384, 257);

  this.Controls.Add(this.panel1);

  this.Controls.Add(this.textBox1);

  this.Controls.Add(this.label_class);

  this.Controls.Add(this.label_title);

  this.Controls.Add(this.button1);

  this.Name = "Form1";

  this.Text = "貼り付けくん";

  this.ResumeLayout(false);

  this.PerformLayout();

 

 

  #endregion

 

  private System.Windows.Forms.Button button1;

  private System.Windows.Forms.Label label_title;

  private System.Windows.Forms.Label label_class;

  private System.Windows.Forms.TextBox textBox1;

  private System.Windows.Forms.Panel panel1;

  }

  }

  ```

  

 

  ---

 

 

  クリップボードが汚れるのを許容できるなら、この方式のほうがいいと思います。