WP7-XNA 多点触摸

XNA中对游戏的控制必然用到触摸事件（WindowsPhone的XNA涉及到的按钮只有一个那就是BACK按钮，其余的交互都必须通过触摸事件来完成）

XNA处理触摸事件的命名空间是 Microsoft.Xna.Framework.Input.Touch （官方示例文档 ： http://msdn.microsoft.com/en-us/library/ff434208.aspx API：http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.input.touch.aspx）

文档中提到处理触摸事件的示例代码如下：

// Process touch events
TouchCollection touchCollection = TouchPanel.GetState();
foreach (TouchLocation tl in touchCollection)
{
    if ((tl.State == TouchLocationState.Pressed)
            || (tl.State == TouchLocationState.Moved))
    {

        // add sparkles based on the touch location
        sparkles.Add(new Sparkle(tl.Position.X,
                 tl.Position.Y, ttms));

    }
}

新建一个项目，叫TouchTest吧~

将上述代码粘贴到Game1.cs的Update方法中，为了测试方便，加入Debug代码。

查看API介绍可知：

TouchLocation 用来保存某一个触摸点的状态信息。

TouchCollection  是保存了当前所有触控状态（TouchLocation）的集合。

然后可以再代码中查看这些类包括的属性，以下摘录个人觉得比较有用的属性列出：

TouchLocation ：

State  触摸状态，包含4个状态

     > TouchLocationState.Pressed 表示屏幕被触摸时手指按下的一瞬间

     > TouchLocationState.Moved 表示手指按下后正在移动，经过测试可知，在手指按下的一瞬间State为Pressed ，在手指按下后抬起前这段时间内的状态均是Moved

     > TouchLocationState.Invalid 无效状态，测试没有出现这个状态，官方描述是This touch location position is invalid. Typically, you will encounter this state when a new touch location attempts to get the previous state of itself.

     > TouchLocationState.Released 表示手指抬起的一瞬间

ID 表示当前触摸事件的ID，一个完成的触控事件的过程应该是“Pressed  -> Moved  -> Released ”在这个过程中ID是一致的，用来在多点触摸时区分触摸的每个点。

Position 触摸位置，包含两个属性

     > X 当前触摸位置的X轴坐标

     > Y 当前触摸位置的Y轴坐标

     （横屏全屏情况下，屏幕的左上角坐标为（0，0）右下角坐标为（800,480））

TouchCollection：

Count 当前有几个点被触摸

比较常用的就是上面这些属性。

使用log记录这些属性。

调整后的测试代码如下：

protected override void Update(GameTime gameTime)
{
    // Allows the game to exit
    if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
        this.Exit();

    // TODO: Add your update logic here
    TouchCollection touchCollection = TouchPanel.GetState();
    foreach (TouchLocation tl in touchCollection)
    {
        if (tl.State == TouchLocationState.Pressed)
        {
            Debug.WriteLine("ID " + tl.Id + " Count:" + touchCollection.Count + " Pressed (" + (float)tl.Position.X + "," + (float)tl.Position.Y + ")");
        }
        if (tl.State == TouchLocationState.Moved)
        {
            Debug.WriteLine("ID " + tl.Id + " Count:" + touchCollection.Count + " Moved (" + (float)tl.Position.X + "," + (float)tl.Position.Y + ")");
        }
        if (tl.State == TouchLocationState.Invalid)
        {
            Debug.WriteLine("ID " + tl.Id + " Count:" + touchCollection.Count + " Invalid (" + (float)tl.Position.X + "," + (float)tl.Position.Y + ")");
        }
        if (tl.State == TouchLocationState.Released)
        {
            Debug.WriteLine("ID " + tl.Id + " Count:" + touchCollection.Count + " Released (" + (float)tl.Position.X + "," + (float)tl.Position.Y + ")");
        }
    }


    base.Update(gameTime);
}

测试得到的日志如下：（测试时的动作是：“两个手指一起温柔的在屏幕上轻点一下”，官方提供的模拟器只能支持单点触摸，再真机上调试可以得到多个点得数据（我用的是Mozart最多可以得到4个点的数据，（但是偶尔很快地用五个指头一起点能得到5个点的数据。。）））

'taskhost.exe' (Managed): Loaded 'mscorlib.dll'
'taskhost.exe' (Managed): Loaded 'System.Windows.RuntimeHost.dll'
'taskhost.exe' (Managed): Loaded 'System.dll'
'taskhost.exe' (Managed): Loaded 'System.Windows.dll'
'taskhost.exe' (Managed): Loaded 'System.Net.dll'
'taskhost.exe' (Managed): Loaded 'System.Core.dll'
'taskhost.exe' (Managed): Loaded 'System.Xml.dll'
'taskhost.exe' (Managed): Loaded '\Applications\Install\6F53E388-71A5-4106-A3B2-609A945B2BAA\Install\TouchTest.dll', Symbols loaded.
'taskhost.exe' (Managed): Loaded 'Microsoft.Xna.Framework.Game.dll'
'taskhost.exe' (Managed): Loaded 'Microsoft.Xna.Framework.Graphics.dll'
'taskhost.exe' (Managed): Loaded 'Microsoft.Xna.Framework.dll'
'taskhost.exe' (Managed): Loaded 'Microsoft.Phone.Interop.dll'
'taskhost.exe' (Managed): Loaded 'Microsoft.Phone.dll'
'taskhost.exe' (Managed): Loaded 'Microsoft.Xna.Framework.Input.Touch.dll'
A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll
'taskhost.exe' (Managed): Loaded 'Microsoft.Xna.Framework.GamerServices.dll'
ID 24182784 Count:1 Pressed (515,159)
ID 24182784 Count:2 Moved (521,158)
ID 24182785 Count:2 Pressed (161,353)
ID 24182784 Count:2 Moved (522,157)
ID 24182785 Count:2 Moved (164,352)
ID 24182784 Count:2 Moved (521,156)
ID 24182785 Count:2 Moved (162,350)
ID 24182784 Count:2 Released (521,156)
ID 24182785 Count:2 Released (162,350)
A first chance exception of type 'System.Threading.ThreadAbortException' occurred in Microsoft.Xna.Framework.dll
The thread '<No Name>' (0x1b44096e) has exited with code 0 (0x0).
The thread '<No Name>' (0x1aad047a) has exited with code 0 (0x0).
The thread '<No Name>' (0x1add086a) has exited with code 0 (0x0).
The program '[463930110] taskhost.exe: Managed' has exited with code 0 (0x0).

（taskhost.exe 那些是程序加载日志可以忽略，重点关注类似“ID 24182784 Count:1 Pressed (515,159)”这样的行）

Tips ：

测试结果可知，我的动作是两个手指一起按得，但是在实际的到的数据来看 我手指触摸的时机，还是有点差别的,所以在开发中要注意这一点。涉及到用户体验啊~~

还有观察坐标可知，即使在我的感觉是轻点了一下，但是实际上我点击的时候手指还是会有轻微的移动的。这些都是开发的时候自定义手势的时候要考虑的问题~~