if (picturebox1.Visible = true) 
       { 
         if (picturebox2.Visible = false) 
         {  
         } 
         else if (picturebox3.Visible = false) 
         { 
           picturebox4.Width = (this.Width - picturebox1.Location.x) - (this.Width - picturebox2.Location.X - picturebox1.Width); 
           picturebox4.Location = new Point(picturebox1.Location.X, picturebox1.Location.Y + picturebox1.Height); 
         } 
         else 
         { 
           picturebox4.Width = (this.Width - picturebox1.Location.x) - (this.Width - picturebox3.Location.X - picturebox1.Width ); 
           picturebox4.Location = new Point(picturebox1.Location.X, picturebox1.Location.Y + picturebox1.Height); 
         } 
       } 
       else if (picturebox2.Visible = true) 
       { 
         if (picturebox2.Visible = false) 
         { 
         } 
         else if (picturebox3.Visible = false) 
         { 
           picturebox4.Width = (this.Width - picturebox2.Location.x) - (this.Width - picturebox2.Location.X - picturebox2.Width); 
           picturebox4.Location = new Point(picturebox2.Location.X, picturebox2.Location.Y + picturebox2.Height); 
         } 
         else 
         { 
           picturebox4.Width = (this.Width - picturebox2.Location.x) - (this.Width - picturebox3.Location.X - picturebox2.Width); 
           picturebox4.Location = new Point(picturebox2.Location.X, picturebox2.Location.Y + picturebox2.Height); 
         } 
       } 
       else if (picturebox3.Visible = true) 
       { 
         picturebox4.Width = (this.Width - picturebox3.Location.x) - (this.Width - picturebox3.Location.X - picturebox3.Width); 
         picturebox4.Location = new Point(picturebox3.Location.X, picturebox3.Location.Y + picturebox3.Height); 
       } 
       else 
       { 
         MessageBox.Show("3个图片都没有显示"); 
       }