好吧，我发现了这个问题。
问题：
在使用 gain() API 时，我们必须在每个事件中设置点的压力和大小。
为了
obtain(long, long, int, int, android.view.MotionEvent.PointerProperties[],
android.view.MotionEvent.PointerCoords[], int, int, float, float, int, int, int, int)
PointerCoords[]，我们必须将压力和大小设置为 1，默认值为 0。
为了
public static MotionEvent obtain (long downTime, long eventTime, int action,
float x, float y, int metaState)
Create a new MotionEvent, filling in a subset of the basic motion values.
Those not specified here are: device id (always 0), pressure and size (always 1),
x and y precision (always 1), and edgeFlags (always 0).
since the default pressure and size are 1, so we don't need to set them.
我创建手势的技巧：
1.遵循真实的手势序列，因为我们要模拟真实的手势
覆盖 onTouchEvent() 以检查应用程序接收到的真实事件。这些事件也可以用于比较真实用户的触摸事件和生成的触摸事件以浏览器为例：
a) @Override public boolean onTouchEvent(MotionEvent event) { Log.i("WebView", event.toString() + event.getAction()); boolean rt = super.onTouchEvent(event); 返回rt；}
手动触摸屏从 a) 中的 onTouchEvent() 获取真实的手势序列。我们可以在生成事件时遵循事件顺序。-- 如果我们不遵循手势事件序列，则检测事件可能会被拒绝。
这是缩放手势的有效事件序列，（所有事件的downTime都是相同的）
一世。一个起点的 ACTION_DOWN
ii. ACTION_POINTER_2_DOWN 的两个起点
iii.两个中间点的ACTION_MOVE
iv. ACTION_POINTER_2_UP 两个端点
v. 一个端点的 ACTION_UP
2.正确使用API MotionEvent.obtain
公共静态 MotionEvent 获取（long downTime、long eventTime、int action、float x、float y、int metaState）
和
公共静态 MotionEvent 获得（long，long，int，int，android.view.MotionEvent.PointerProperties[]，android.view.MotionEvent.PointerCoords[]，int，int，float，float，int，int，int，int）
第一个通常用于单点手势，如滑动、滚动、单击等。此功能的参数（压力、大小、xPresion、yPresion）均设置为 1。
而第二种是比较通用的一种，可以用于多点触控事件的生成。而对于第二个，我们必须将每个触摸点的指针坐标中的压力、大小设置为 1。
这是生成缩放手势的示例：
public static void generateZoomGesture(Instrumentation inst,
long startTime, boolean ifMove, GestureInfo.Point startPoint1,
GestureInfo.Point startPoint2, GestureInfo.Point endPoint1,
GestureInfo.Point endPoint2, int duration) {
if (inst == null || startPoint1 == null
|| (ifMove && endPoint1 == null)) {
return;
}
long eventTime = startTime;
long downTime = startTime;
MotionEvent event;
float eventX1, eventY1, eventX2, eventY2;
eventX1 = startPoint1.x;
eventY1 = startPoint1.y;
eventX2 = startPoint2.x;
eventY2 = startPoint2.y;
// specify the property for the two touch points
PointerProperties[] properties = new PointerProperties[2];
PointerProperties pp1 = new PointerProperties();
pp1.id = 0;
pp1.toolType = MotionEvent.TOOL_TYPE_FINGER;
PointerProperties pp2 = new PointerProperties();
pp2.id = 1;
pp2.toolType = MotionEvent.TOOL_TYPE_FINGER;
properties[0] = pp1;
properties[1] = pp2;
//specify the coordinations of the two touch points
//NOTE: you MUST set the pressure and size value, or it doesn't work
PointerCoords[] pointerCoords = new PointerCoords[2];
PointerCoords pc1 = new PointerCoords();
pc1.x = eventX1;
pc1.y = eventY1;
pc1.pressure = 1;
pc1.size = 1;
PointerCoords pc2 = new PointerCoords();
pc2.x = eventX2;
pc2.y = eventY2;
pc2.pressure = 1;
pc2.size = 1;
pointerCoords[0] = pc1;
pointerCoords[1] = pc2;
//////////////////////////////////////////////////////////////
// events sequence of zoom gesture
// 1. send ACTION_DOWN event of one start point
// 2. send ACTION_POINTER_2_DOWN of two start points
// 3. send ACTION_MOVE of two middle points
// 4. repeat step 3 with updated middle points (x,y),
// until reach the end points
// 5. send ACTION_POINTER_2_UP of two end points
// 6. send ACTION_UP of one end point
//////////////////////////////////////////////////////////////
// step 1
event = MotionEvent.obtain(downTime, eventTime,
MotionEvent.ACTION_DOWN, 1, properties,
pointerCoords, 0, 0, 1, 1, 0, 0, 0, 0 );
inst.sendPointerSync(event);
//step 2
event = MotionEvent.obtain(downTime, eventTime,
MotionEvent.ACTION_POINTER_2_DOWN, 2,
properties, pointerCoords, 0, 0, 1, 1, 0, 0, 0, 0);
inst.sendPointerSync(event);
//step 3, 4
if (ifMove) {
int moveEventNumber = 1;
moveEventNumber = duration / EVENT_MIN_INTERVAL;
float stepX1, stepY1, stepX2, stepY2;
stepX1 = (endPoint1.x - startPoint1.x) / moveEventNumber;
stepY1 = (endPoint1.y - startPoint1.y) / moveEventNumber;
stepX2 = (endPoint2.x - startPoint2.x) / moveEventNumber;
stepY2 = (endPoint2.y - startPoint2.y) / moveEventNumber;
for (int i = 0; i < moveEventNumber; i++) {
// update the move events
eventTime += EVENT_MIN_INTERVAL;
eventX1 += stepX1;
eventY1 += stepY1;
eventX2 += stepX2;
eventY2 += stepY2;
pc1.x = eventX1;
pc1.y = eventY1;
pc2.x = eventX2;
pc2.y = eventY2;
pointerCoords[0] = pc1;
pointerCoords[1] = pc2;
event = MotionEvent.obtain(downTime, eventTime,
MotionEvent.ACTION_MOVE, 2, properties,
pointerCoords, 0, 0, 1, 1, 0, 0, 0, 0);
inst.sendPointerSync(event);
}
}
//step 5
pc1.x = endPoint1.x;
pc1.y = endPoint1.y;
pc2.x = endPoint2.x;
pc2.y = endPoint2.y;
pointerCoords[0] = pc1;
pointerCoords[1] = pc2;
eventTime += EVENT_MIN_INTERVAL;
event = MotionEvent.obtain(downTime, eventTime,
MotionEvent.ACTION_POINTER_2_UP, 2, properties,
pointerCoords, 0, 0, 1, 1, 0, 0, 0, 0);
inst.sendPointerSync(event);
// step 6
eventTime += EVENT_MIN_INTERVAL;
event = MotionEvent.obtain(downTime, eventTime,
MotionEvent.ACTION_UP, 1, properties,
pointerCoords, 0, 0, 1, 1, 0, 0, 0, 0 );
inst.sendPointerSync(event);
}