ViewConfiguration

ViewConfiguration是view包下的一个子类，这里记录了view的一些基础数据。比如最大速率和最小速率、滑动距离、
滚动距离、fling距离、等。

用法
利用get方法获取当前VIEW的Config对象
ViewConfiguration.get(getContext());

一些方法

1.在可滑动的控件中用于区别单击子控件和滑动操作的一个伐值。

mTouchSlop = configuration.getScaledTouchSlop();

2.用于设置最小加速率和最大速率.

mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();

3.滚动距离

mOverscrollDistance = configuration.getScaledOverscrollDistance();

4.fling距离

mOverflingDistance = configuration.getScaledOverflingDistance();

5.摩擦力，用来计算减速度

mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction());

/**

• 包含了方法和标准的常量用来设置UI的超时、大小和距离
  /
  public class ViewConfiguration {
  // 设定水平滚动条的宽度和垂直滚动条的高度，单位是像素px
  private static final int SCROLL_BAR_SIZE = 10;
  //定义滚动条逐渐消失的时间，单位是毫秒
  private static final int SCROLL_BAR_FADE_DURATION = 250;
  // 默认的滚动条多少秒之后消失，单位是毫秒
  private static final int SCROLL_BAR_DEFAULT_DELAY = 300;
  // 定义边缘地方褪色的长度
  private static final int FADING_EDGE_LENGTH = 12;
  //定义子控件按下状态的持续事件
  private static final int PRESSED_STATE_DURATION = 125;
  //定义一个按下状态转变成长按状态的转变时间
  private static final int LONG_PRESS_TIMEOUT = 500;
  //定义用户在按住适当按钮，弹出全局的对话框的持续时间
  private static final int GLOBAL_ACTIONS_KEY_TIMEOUT = 500;
  //定义一个touch事件中是点击事件还是一个滑动事件所需的时间，如果用户在这个时间之内滑动，那么就认为是一个点击事件
  private static final int TAP_TIMEOUT = 115;
  /*
  • Defines the duration in milliseconds we will wait to see if a touch event
  • is a jump tap. If the user does not complete the jump tap within this interval, it is
  • considered to be a tap.
    /
    //定义一个touch事件时候是一个点击事件。如果用户在这个时间内没有完成这个点击，那么就认为是一个点击事件
    private static final int JUMP_TAP_TIMEOUT = 500;
    //定义双击事件的间隔时间
    private static final int DOUBLE_TAP_TIMEOUT = 300;
    //定义一个缩放控制反馈到用户界面的时间
    private static final int ZOOM_CONTROLS_TIMEOUT = 3000;
    /*
  • Inset in pixels to look for touchable content when the user touches the edge of the screen
    /
    private static final int EDGE_SLOP = 12;
    /*
  • Distance a touch can wander before we think the user is scrolling in pixels
    /
    private static final int TOUCH_SLOP = 16;
    /*
  • Distance a touch can wander before we think the user is attempting a paged scroll
  • (in dips)
    /
    private static final int PAGING_TOUCH_SLOP = TOUCH_SLOP * 2;
    /*
  • Distance between the first touch and second touch to still be considered a double tap
    /
    private static final int DOUBLE_TAP_SLOP = 100;
    /*
  • Distance a touch needs to be outside of a window's bounds for it to
  • count as outside for purposes of dismissing the window.
    /
    private static final int WINDOW_TOUCH_SLOP = 16;
    //用来初始化fling的最小速度，单位是每秒多少像素
    private static final int MINIMUM_FLING_VELOCITY = 50;
    //用来初始化fling的最大速度，单位是每秒多少像素
    private static final int MAXIMUM_FLING_VELOCITY = 4000;
    //视图绘图缓存的最大尺寸，以字节表示。在ARGB888格式下，这个尺寸应至少等于屏幕的大小
    @Deprecated
    private static final int MAXIMUM_DRAWING_CACHE_SIZE = 320 * 480 * 4; // HVGA screen, ARGB8888
    //flings和scrolls摩擦力度大小的系数
    private static float SCROLL_FRICTION = 0.015f;
    /*
  • Max distance to over scroll for edge effects
    /
    private static final int OVERSCROLL_DISTANCE = 0;
    /*
  • Max distance to over fling for edge effects
    */
    private static final int OVERFLING_DISTANCE = 4;
    }