申明：
参考：http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2013/0226/914.html
下面实现如何通过应用层支持多点触控操作，对于常规的控件触控操实现onTouchEvent()方法来处理。同时对onTouchEvent方法的参数MotionEvent进行一些了解。
正文：
下面会用两个应用示例来初步学习一下Android中的多点触控。
示例一（DemoMultiTouch-Canvas）：
核心技术介绍
本示例是在SurfaceView中利用Canvas来展示用户的多点触控，不过核心技术还是一个常见的方法：onTouchEvent(MotionEvent event)
MotionEvent有以下几个方法需要大家注意一下，不过了是一些常见的方法，如果你onTouchEvent使用得多的话。
event.getAction()
// 获取触控动作比如ACTION_DOWN
event.getPointerCount(); // 获取触控点的数量，比如2则可能是两个手指同时按压屏幕
event.getPointerId(nID); // 对于每个触控的点的细节，我们可以通过一个循环执行getPointerId方法获取索引
event.getX(nID); // 获取第nID个触控点的x位置
event.getY(nID); // 获取第nID个点触控的y位置
event.getPressure(nID); // LCD可以感应出用户的手指压力，当然具体的级别由驱动和物理硬件决定的
event.getDownTime() // 按下开始时间
event.getEventTime() // 事件结束时间
event.getEventTime()-event.getDownTime()); // 总共按下时花费时间
代码展示：
public class MTView extends SurfaceView implements SurfaceHolder.Callback {
private static final int MAX_TOUCHPOINTS = 10;
private static final String START_TEXT = "请随便触摸屏幕进行测试";
private Paint textPaint = new Paint();
private Paint touchPaints[] = new Paint[MAX_TOUCHPOINTS];
private int colors[] = new int[MAX_TOUCHPOINTS];
private int width, height;
private float scale = 1.0f;
public MTView(Context context) {
super(context);
SurfaceHolder holder = getHolder();
holder.addCallback(this);
setFocusable(true); // 确保我们的View能获得输入焦点
setFocusableInTouchMode(true); // 确保能接收到触屏事件
init();
}
private void init() {
// 初始化10个不同颜色的画笔
textPaint.setColor(Color.WHITE);
colors[0] = Color.BLUE;
colors[1] = Color.RED;
colors[2] = Color.GREEN;
colors[3] = Color.YELLOW;
colors[4] = Color.CYAN;
colors[5] = Color.MAGENTA;
colors[6] = Color.DKGRAY;
colors[7] = Color.WHITE;
colors[8] = Color.LTGRAY;
colors[9] = Color.GRAY;
for (int i = 0; i < MAX_TOUCHPOINTS; i++) {
touchPaints[i] = new Paint();
touchPaints[i].setColor(colors[i]);
}
}
/**
* 处理触屏事件
*/
@Override
public boolean onTouchEvent(MotionEvent event) {
// 获得屏幕触点数量
int pointerCount = event.getPointerCount();
if (pointerCount > MAX_TOUCHPOINTS) {
pointerCount = MAX_TOUCHPOINTS;
}
// 锁定Canvas,开始进行相应的界面处理
Canvas c = getHolder().lockCanvas();
if (c != null) {
c.drawColor(Color.BLACK);
if (event.getAction() == MotionEvent.ACTION_UP) {
// 当手离开屏幕时，清屏
} else {
// 在每一个触点上绘制一个十字和坐标信息
for (int i = 0; i < pointerCount; i++) {
int id = event.getPointerId(i);
int x = (int) event.getX(i);
int y = (int) event.getY(i);
drawCrosshairsAndText(x, y, touchPaints[id], i, id, c);
}
// 在每一个触点上绘制一个圆
for (int i = 0; i < pointerCount; i++) {
int id = event.getPointerId(i);
int x = (int) event.getX(i);
int y = (int) event.getY(i);
drawCircle(x, y, touchPaints[id], c);
}
}
// 画完后，unlock
getHolder().unlockCanvasAndPost(c);
}
return true;
}
/**
* 画十字及坐标信息
*
* @param x
* @param y
* @param paint
* @param ptr
* @param id
* @param c
*/
private void drawCrosshairsAndText(int x, int y, Paint paint, int ptr,
int id, Canvas c) {
c.drawLine(0, y, width, y, paint);
c.drawLine(x, 0, x, height, paint);
int textY = (int) ((15 + 20 * ptr) * scale);
c.drawText("x" + ptr + "=" + x, 10 * scale, textY, textPaint);
c.drawText("y" + ptr + "=" + y, 70 * scale, textY, textPaint);
c.drawText("id" + ptr + "=" + id, width - 55 * scale, textY, textPaint);
}
/**
* 画圆
*
* @param x
* @param y
* @param paint
* @param c
*/
private void drawCircle(int x, int y, Paint paint, Canvas c) {
c.drawCircle(x, y, 40 * scale, paint);
}
/**
* 进入程序时背景画成黑色，然后把START_TEXT写到屏幕
*/
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
this.width = width;
this.height = height;
if (width > height) {
this.scale = width / 480f;
} else {
this.scale = height / 480f;
}
textPaint.setTextSize(14 * scale);
Canvas c = getHolder().lockCanvas();
if (c != null) {
c.drawColor(Color.BLACK);
float tWidth = textPaint.measureText(START_TEXT);
c.drawText(START_TEXT, width / 2 - tWidth / 2, height / 2, textPaint);
getHolder().unlockCanvasAndPost(c);
}
}
public void surfaceCreated(SurfaceHolder holder) {
}
public void surfaceDestroyed(SurfaceHolder holder) {
}
}
使用上也是so easy：
setContentView(new MTView(this));
运行效果图：
示例二（DemoMultiTouch-ImageView）：
通过多点触屏放大或缩小图像 beforeLenght用来保存前一时间两点之间的距离 afterLenght用来保存当前时间两点之间的距离
public void scaleWithFinger(MotionEvent event) {
float moveX = event.getX(1) - event.getX(0);
float moveY = event.getY(1) - event.getY(0);
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
beforeLenght = (float) Math.sqrt((moveX * moveX)
+ (moveY * moveY));
break;
case MotionEvent.ACTION_MOVE:
// 得到两个点之间的长度
afterLenght = (float) Math.sqrt((moveX * moveX)
+ (moveY * moveY));
float gapLenght = afterLenght - beforeLenght;
if (gapLenght == 0) {
break;
}
// 如果当前时间两点距离大于前一时间两点距离，则传0，否则传1
if (gapLenght > 0) {
this.setScale(scale, 0);
} else {
this.setScale(scale, 1);
}
beforeLenght = afterLenght;
break;
}
}
}
让图片跟随手指触屏的位置移动 beforeX、Y是用来保存前一位置的坐标 afterX、Y是用来保存当前位置的坐标。它们的差值就是ImageView各坐标的增加或减少值。
public void moveWithFinger(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
beforeX = event.getX();
beforeY = event.getY();
break;
case MotionEvent.ACTION_MOVE:
afterX = event.getX();
afterY = event.getY();
this.setLocation((int) (afterX - beforeX),
(int) (afterY - beforeY));
beforeX = afterX;
beforeY = afterY;
break;
case MotionEvent.ACTION_UP:
break;
}
}
private void setScale(float temp, int flag) {
if (flag == 0) {
this.setFrame(this.getLeft() - (int) (temp * this.getWidth()),
this.getTop() - (int) (temp * this.getHeight()),
this.getRight() + (int) (temp * this.getWidth()),
this.getBottom() + (int) (temp * this.getHeight()));
} else {
this.setFrame(this.getLeft() + (int) (temp * this.getWidth()),
this.getTop() + (int) (temp * this.getHeight()),
this.getRight() - (int) (temp * this.getWidth()),
this.getBottom() - (int) (temp * this.getHeight()));
}
}
public boolean onTouchEvent(MotionEvent event) {
if (inView(imageView, event)) {
if (event.getPointerCount() == 2) {
imageView.scaleWithFinger(event);
} else if (event.getPointerCount() == 1) {
imageView.moveWithFinger(event);
}
}
return true;
}