手机链接蓝牙鼠标后，可以用鼠标操作手机，当鼠标移动到某控件后，它的形状可能从箭头变为小手（文本链接等）。
辣么google，如何实现的呢？
一、先来看看图片：
有好多鼠标的图片。目录随意一个存储图片的目录即可，例如：8trunk/frameworks/base/core/res/res/drawable-mdpi
二、主题和属性控制：
一步一步来，不急知道google如何做到鼠标移动，指针形状发生变化的逻辑。
先来了解下，这些图片如何被加载的。
一般的，google不会直接在code各种使用图片，一般的都在style里写好，在code中进行解析加载。
1.style中：
/frameworks/base/core/res/res/values/styles.xml
<style name="Pointer">
1351 <item name="pointerIconArrow">@drawable/pointer_arrow_icon</item>
1352 <item name="pointerIconSpotHover">@drawable/pointer_spot_hover_icon</item>
1353 <item name="pointerIconSpotTouch">@drawable/pointer_spot_touch_icon</item>
1354 <item name="pointerIconSpotAnchor">@drawable/pointer_spot_anchor_icon</item>
1355 <item name="pointerIconHand">@drawable/pointer_hand_icon</item>
1356 <item name="pointerIconContextMenu">@drawable/pointer_context_menu_icon</item>
1357 <item name="pointerIconHelp">@drawable/pointer_help_icon</item>
1358 <item name="pointerIconWait">@drawable/pointer_wait_icon</item>
1359 <item name="pointerIconCell">@drawable/pointer_cell_icon</item>
1360 <item name="pointerIconCrosshair">@drawable/pointer_crosshair_icon</item>
1361 <item name="pointerIconText">@drawable/pointer_text_icon</item>
1362 <item name="pointerIconVerticalText">@drawable/pointer_vertical_text_icon</item>
1363 <item name="pointerIconAlias">@drawable/pointer_alias_icon</item>
1364 <item name="pointerIconCopy">@drawable/pointer_copy_icon</item>
1365 <item name="pointerIconAllScroll">@drawable/pointer_all_scroll_icon</item>
1366 <item name="pointerIconNodrop">@drawable/pointer_nodrop_icon</item>
1367 <item name="pointerIconHorizontalDoubleArrow">
1368 @drawable/pointer_horizontal_double_arrow_icon
1369 </item>
1370 <item name="pointerIconVerticalDoubleArrow">
1371 @drawable/pointer_vertical_double_arrow_icon
1372 </item>
1373 <item name="pointerIconTopRightDiagonalDoubleArrow">
1374 @drawable/pointer_top_right_diagonal_double_arrow_icon
1375 </item>
1376 <item name="pointerIconTopLeftDiagonalDoubleArrow">
1377 @drawable/pointer_top_left_diagonal_double_arrow_icon
1378 </item>
1379 <item name="pointerIconZoomIn">@drawable/pointer_zoom_in_icon</item>
1380 <item name="pointerIconZoomOut">@drawable/pointer_zoom_out_icon</item>
1381 <item name="pointerIconGrab">@drawable/pointer_grab_icon</item>
1382 <item name="pointerIconGrabbing">@drawable/pointer_grabbing_icon</item>
1383 </style>
1384
1385 <style name="LargePointer">
1386 <item name="pointerIconArrow">@drawable/pointer_arrow_large_icon</item>
1387 <item name="pointerIconSpotHover">@drawable/pointer_spot_hover_icon</item>
1388 <item name="pointerIconSpotTouch">@drawable/pointer_spot_touch_icon</item>
1389 <item name="pointerIconSpotAnchor">@drawable/pointer_spot_anchor_icon</item>
1390 <item name="pointerIconHand">@drawable/pointer_hand_large_icon</item>
1391 <item name="pointerIconContextMenu">@drawable/pointer_context_menu_large_icon</item>
1392 <item name="pointerIconHelp">@drawable/pointer_help_large_icon</item>
1393 <!-- TODO: create large wait icon. -->
1394 <item name="pointerIconWait">@drawable/pointer_wait_icon</item>
1395 <item name="pointerIconCell">@drawable/pointer_cell_large_icon</item>
1396 <item name="pointerIconCrosshair">@drawable/pointer_crosshair_large_icon</item>
1397 <item name="pointerIconText">@drawable/pointer_text_large_icon</item>
1398 <item name="pointerIconVerticalText">@drawable/pointer_vertical_text_large_icon</item>
1399 <item name="pointerIconAlias">@drawable/pointer_alias_large_icon</item>
1400 <item name="pointerIconCopy">@drawable/pointer_copy_large_icon</item>
1401 <item name="pointerIconAllScroll">@drawable/pointer_all_scroll_large_icon</item>
1402 <item name="pointerIconNodrop">@drawable/pointer_nodrop_large_icon</item>
1403 <item name="pointerIconHorizontalDoubleArrow">
1404 @drawable/pointer_horizontal_double_arrow_large_icon
1405 </item>
1406 <item name="pointerIconVerticalDoubleArrow">
1407 @drawable/pointer_vertical_double_arrow_large_icon
1408 </item>
1409 <item name="pointerIconTopRightDiagonalDoubleArrow">
1410 @drawable/pointer_top_right_diagonal_double_arrow_large_icon
1411 </item>
1412 <item name="pointerIconTopLeftDiagonalDoubleArrow">
1413 @drawable/pointer_top_left_diagonal_double_arrow_large_icon
1414 </item>
1415 <item name="pointerIconZoomIn">@drawable/pointer_zoom_in_large_icon</item>
1416 <item name="pointerIconZoomOut">@drawable/pointer_zoom_out_large_icon</item>
1417 <item name="pointerIconGrab">@drawable/pointer_grab_large_icon</item>
1418 <item name="pointerIconGrabbing">@drawable/pointer_grabbing_large_icon</item>
1419 </style>
14202.code中：
xml中定义好了，必然会在code进行加载处理。
扫描二维码关注公众号，回复：
2514479 查看本文章
关注一个类：PointerIcon.java，可以看到，不同的type，会加载不同的图片。
现在大概有点想法了吧，不同控件设置了相应的type，根据这些type显示相应的鼠标形状。
private static int getSystemIconTypeIndex(int type) {
switch (type) {
case TYPE_ARROW:
return com.android.internal.R.styleable.Pointer_pointerIconArrow;
case TYPE_SPOT_HOVER:
return com.android.internal.R.styleable.Pointer_pointerIconSpotHover;
case TYPE_SPOT_TOUCH:
return com.android.internal.R.styleable.Pointer_pointerIconSpotTouch;
case TYPE_SPOT_ANCHOR:
return com.android.internal.R.styleable.Pointer_pointerIconSpotAnchor;
case TYPE_HAND:
return com.android.internal.R.styleable.Pointer_pointerIconHand;
case TYPE_CONTEXT_MENU:
return com.android.internal.R.styleable.Pointer_pointerIconContextMenu;
case TYPE_HELP:
return com.android.internal.R.styleable.Pointer_pointerIconHelp;
case TYPE_WAIT:
return com.android.internal.R.styleable.Pointer_pointerIconWait;
case TYPE_CELL:
return com.android.internal.R.styleable.Pointer_pointerIconCell;
case TYPE_CROSSHAIR:
return com.android.internal.R.styleable.Pointer_pointerIconCrosshair;
case TYPE_TEXT:
return com.android.internal.R.styleable.Pointer_pointerIconText;
case TYPE_VERTICAL_TEXT:
return com.android.internal.R.styleable.Pointer_pointerIconVerticalText;
case TYPE_ALIAS:
return com.android.internal.R.styleable.Pointer_pointerIconAlias;
case TYPE_COPY:
return com.android.internal.R.styleable.Pointer_pointerIconCopy;
case TYPE_ALL_SCROLL:
return com.android.internal.R.styleable.Pointer_pointerIconAllScroll;
case TYPE_NO_DROP:
return com.android.internal.R.styleable.Pointer_pointerIconNodrop;
case TYPE_HORIZONTAL_DOUBLE_ARROW:
return com.android.internal.R.styleable.Pointer_pointerIconHorizontalDoubleArrow;
case TYPE_VERTICAL_DOUBLE_ARROW:
return com.android.internal.R.styleable.Pointer_pointerIconVerticalDoubleArrow;
case TYPE_TOP_RIGHT_DIAGONAL_DOUBLE_ARROW:
return com.android.internal.R.styleable.
Pointer_pointerIconTopRightDiagonalDoubleArrow;
case TYPE_TOP_LEFT_DIAGONAL_DOUBLE_ARROW:
return com.android.internal.R.styleable.
Pointer_pointerIconTopLeftDiagonalDoubleArrow;
case TYPE_ZOOM_IN:
return com.android.internal.R.styleable.Pointer_pointerIconZoomIn;
case TYPE_ZOOM_OUT:
return com.android.internal.R.styleable.Pointer_pointerIconZoomOut;
case TYPE_GRAB:
return com.android.internal.R.styleable.Pointer_pointerIconGrab;
case TYPE_GRABBING:
return com.android.internal.R.styleable.Pointer_pointerIconGrabbing;
default:
return 0;
}
}
三、如何做到移动的时候，改变鼠标的形状：
从1-2，基本知道了，google是根据type加载不同的图片来显示的。
那么它如何知道什么时候加载那张图片？比如：超链接要显示”小手“，文本编辑要显示”竖线“的呢？
下面介绍一下相关逻辑，不过前提是需要对android 输入事件处理机制，有个基本的了解，不然可能看起来有点蒙。
1.整体逻辑概述：
当输入事件过来的时候(鼠标移动)，Input处理到ViewRootImpl的时候，ViewRootImpl是领导，它以巡视的角度进行处理（顺序描述处理逻辑）：1.当前到啥控件上了；2.这个控件有没有鼠标的图片类型返回来啊？YES显示这个类型的图片（可能是手，竖线等）：NO显示默认的图片（箭头）。
简单概括就是这么一句话。好屌有木有，这么复杂的逻辑，一句话就搞定了^$^。
2.code梳理：
从1，大概知道它怎么处理了。下面看看，代码上如何完成这些的。
需要稍微了解下ViewGroup，ViewRootImpl。
A.ViewRootImpl（涉及很多input派发相关知识，不在展开描述，若不了解，可能会感觉蒙）
根据input事件进行处理，那么肯定是ViewRootImpl进行的第一步了。
输入事件处理7阶段的第四阶段：ViewPostImeInputStage
其中函数：中的maybeUpdatePointerIcon(event);就是开始做事情了。
private int processPointerEvent(QueuedInputEvent q) {
maybeUpdatePointerIcon(event); private boolean updatePointerIcon(MotionEvent event) {
final int pointerIndex = 0;
final float x = event.getX(pointerIndex);
final float y = event.getY(pointerIndex);
if (mView == null) {
// E.g. click outside a popup to dismiss it
Slog.d(mTag, "updatePointerIcon called after view was removed");
return false;
}
if (x < 0 || x >= mView.getWidth() || y < 0 || y >= mView.getHeight()) {
// E.g. when moving window divider with mouse
Slog.d(mTag, "updatePointerIcon called with position out of bounds");
return false;
}
final PointerIcon pointerIcon = mView.onResolvePointerIcon(event, pointerIndex);//这里，会进行派发到当前控件，询问是否有鼠标图片，没有肯定默认了，有就会用你的。
final int pointerType = (pointerIcon != null) ?
pointerIcon.getType() : PointerIcon.TYPE_DEFAULT;//拿到图片后，获得对应的type，一对一的关系；TYPE_DEFAULT就是箭头，默认就是这个
if (mPointerIconType != pointerType) {
mPointerIconType = pointerType;//更新成员变量，保存这个图片的type，就是保存当前使用的图片，后面判断的时候，没有变化，就不用重新设置了
mCustomPointerIcon = null;
if (mPointerIconType != PointerIcon.TYPE_CUSTOM) {
InputManager.getInstance().setPointerIconType(pointerType);//没有自定义，就设置下去；自定义也设置下，调用的接口不一样而已
return true;
}
}
if (mPointerIconType == PointerIcon.TYPE_CUSTOM &&
!pointerIcon.equals(mCustomPointerIcon)) {
mCustomPointerIcon = pointerIcon;
InputManager.getInstance().setCustomPointerIcon(mCustomPointerIcon);//自定义的鼠标图片
}
return true;
}B.ViewGroup中：
从A中，看到要进行派发，查找当前鼠标悬浮的控件，然后看这个控件有么有鼠标图片要设置：mView.onResolvePointerIcon(event, pointerIndex);
其实ViewGroup从code角度是比较复杂的，从思路上又是简单的，为什么这么说：不负责任的说，它就是各种递归。。。就是政府机构一球样（踢皮球），各种遍历，返回调来调去，父子各种调用。
我们简而言之，下面两个函数：
@Override
public PointerIcon onResolvePointerIcon(MotionEvent event, int pointerIndex) {
... ...
final PointerIcon pointerIcon =
dispatchResolvePointerIcon(event, pointerIndex, child);
if (pointerIcon != null) {
if (preorderedList != null) preorderedList.clear();
return pointerIcon;
}
... ...
}
private PointerIcon dispatchResolvePointerIcon(MotionEvent event, int pointerIndex,
View child) {
final PointerIcon pointerIcon;
... ...
pointerIcon = child.onResolvePointerIcon(event, pointerIndex);
... ...
return pointerIcon;
}
这两个就调来调去的，父掉子，结果子还有子，所以子又是父... ...（很形象，viewgroup的遍历，就是这么弄的）
最后，找到了没儿子的儿子，那么就是它了，child.onResolvePointerIcon(event, pointerIndex);
我们举例，这个child就是Button。
Button.java中：返回的是TYPE_HAND。到此，就完事了。
@Override
public PointerIcon onResolvePointerIcon(MotionEvent event, int pointerIndex) {
if (getPointerIcon() == null && isClickable() && isEnabled()) {
return PointerIcon.getSystemIcon(getContext(), PointerIcon.TYPE_HAND);
}
return super.onResolvePointerIcon(event, pointerIndex);
}总结一下：
移动鼠标，遍历当前的控件，控件返回鼠标图片。没移动一下，都会有input事件，所以鼠标图片是”实时“（或者说是及时）更新的。
拿到图片以后，通过InputManager.getInstance().setPointerIconType(pointerType)就设置成功了。
具体的setPointerIconType就不在展开了。
很多没有展开讲，太过详细，反而很难看懂，基本框架了解之后，顺着code，摸摸细节也就逐渐清晰了。