本文实例为大家分享了android绘制触点轨迹的具体代码，供大家参考，具体内容如下
重点函数是onTouchEvent()，所有的触摸事件都会在View的这个函数里面处理
单点触控
单点触控的event是通过event.getAction()获得的，一般最少需要考虑下面这三种情况
MotionEvent.ACTION_DOWN:
- 手指 初次接触到屏幕 时触发。
MotionEvent.ACTION_MOVE:
- 手指 在屏幕上滑动 时触发，会多次触发。
MotionEvent.ACTION_UP:
- 手指 离开屏幕 时触发。
多点触控
多点触控的event是通过event.getActionMasked()获得的，一般最少需要考虑下面这个五种情况，因为有多个点需要处理，所以需要判断event是哪一个触摸点的事件，Android因此导入了比较多的概念，下面通过对关键函数的解析来说明。
注意：方法的说明中添加了我的注释，请留意。另外，每一组函数和这个模块最后都有我写的总结性的文字。
MotionEvent提供了很多看似能直接得到触摸点的方法，但是，这些方法并不是直接拿来能用的，具体的关系如下
getAction()和getActionIndex()以及getActionMasked()
getAction()
/**
* Return the kind of action being performed.
* Consider using {@link #getActionMasked} and {@link #getActionIndex} to retrieve
* the separate masked action and pointer index.
* @return The action, such as {@link #ACTION_DOWN} or
* the combination of {@link #ACTION_POINTER_DOWN} with a shifted pointer index.
*/
public final int getAction() {
return nativeGetAction(mNativePtr);//注意返回值表达式
}getActionIndex()
public static final int ACTION_POINTER_INDEX_MASK = 0xff00;
public static final int ACTION_POINTER_INDEX_SHIFT = 8;
/**
* For {@link #ACTION_POINTER_DOWN} or {@link #ACTION_POINTER_UP}
* as returned by {@link #getActionMasked}, this returns the associated
* pointer index.
* The index may be used with {@link #getPointerId(int)},
* {@link #getX(int)}, {@link #getY(int)}, {@link #getPressure(int)},
* and {@link #getSize(int)} to get information about the pointer that has
* gone down or up.
* @return The index associated with the action.
*/
public final int getActionIndex() {
//这个表达式实际就是说取getAction()函数返回值的高8位
return (nativeGetAction(mNativePtr) & ACTION_POINTER_INDEX_MASK)
>> ACTION_POINTER_INDEX_SHIFT;
}getActionMasked()
public static final int ACTION_MASK = 0xff;
/**
* Return the masked action being performed, without pointer index information.
* Use {@link #getActionIndex} to return the index associated with pointer actions.
* @return The action, such as {@link #ACTION_DOWN} or {@link #ACTION_POINTER_DOWN}.
*/
public final int getActionMasked() {
//这个表达式的意思就是说取getAction()函数的低8位
return nativeGetAction(mNativePtr) & ACTION_MASK;
}总结：这就很简单明了了，Acton包含两个部分，高8位表示触摸点的index，低8位表示具体的事件。
注意这里的触摸点的index，指的是Action中的，而不是event中的，这是两个概念。
getPointerId()和findPointerIndex()
getPointerID()
//注意函数的注释第一句的说明，表示，返回的id叫pointer identifier,是和event里面的数据关联的
/**
* Return the pointer identifier associated with a particular pointer
* data index in this event. The identifier tells you the actual pointer
* number associated with the data, accounting for individual pointers
* going up and down since the start of the current gesture.
* @param pointerIndex Raw index of pointer to retrieve. Value may be from 0
* (the first pointer that is down) to {@link #getPointerCount()}-1.
*/
public final int getPointerId(int pointerIndex) {
return nativeGetPointerId(mNativePtr, pointerIndex);
}findPointerIndex()
//注意函数的注释里面第一句，意思是提供一个pointer identifier,返回event中对应数据的index
//index of data的作用是传给event.getX()等其他的函数来获取坐标等信息
//所以这个函数的名字改成getPointerDataIndex比较合适
/**
* Given a pointer identifier, find the index of its data in the event.
*
* @param pointerId The identifier of the pointer to be found.
* @return Returns either the index of the pointer (for use with
* {@link #getX(int)} et al.), or -1 if there is no data available for
* that pointer identifier.
*/
public final int findPointerIndex(int pointerId) {
return nativeFindPointerIndex(mNativePtr, pointerId);
}总结：这里引入了两个概念，一个是pointer identifier,很好理解，就是指针的id,一个是index of its data.
总结
MotionEvent.getAction返回的是actionIndex和mask的连接体，通过actionIndex可以获取到对应的pointerID,通过pointerID可以获取到对应数据包的ID，然后通过getX()来获取对应的数据信息
基本的使用方法示例
int index = event.getActionIndex();
int id = event.getPointerId(index);
int pointerIndex = event.findPointerIndex(id);
int x=getX(pointerIndex);
int y=getY(pointerIndex);MotionEvent.ACTION_POINTER_DOWN:
- 多点触控时按下手指时触发，如果当前只有一个点，则不会触发此事件。
MotionEvent.ACTION_POINTER_DOWN:
- 多点触控抬起手指时触发，如果当前只有一个点，则不会触发此事件。
MotionEvent.ACTION_DOWN:
- 第一个手指按下时触发
MotionEvent.ACTION_UP:
- 最后一个手指离开时触发
MotionEvent.ACTION_MOVE:
1.所有的手指滑动时触发此事件
2.如果有多个点，同时移动，需要在ACTION_MOVE里面添加循环语句。
3.考虑到刷新效率的问题，可以通过event.getHistoricalX()和event.getHistoricalY()来获取存在缓存中的数据，后面的例子中有说明
实例
获取默认屏幕长和宽的代码
WindowManager manager=(WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);
DisplayMetrics displayMetrics=new DisplayMetrics();
Display display=manager.getDefaultDisplay();
display.getMetrics(displayMetrics);
screenW=displayMetrics.widthPixels;
screenH=displayMetrics.heightPixels;自定义View的代码
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import java.util.HashMap;
import java.util.Map;
public class TouchTraceView extends View
{
Context mContext;
private Paint line_paint, text_paint, countPaint;
int screenW, screenH;
FactoryApplication app;
private int paintColor = Color.RED;
Map<Integer, TouchPoint> pointMap;
float back_x1, back_y1, back_x2, back_y2;
public TouchTraceView(Context context, AttributeSet attr)
{
super(context, attr);
mContext = context;
app = ;//作用仅仅是获取默认屏幕的长和宽
this.screenH = app.screenH;
this.screenW = app.screenW;
pointMap = new HashMap<>();
initPaint();
}
private void initPaint()
{
line_paint = new Paint();
line_paint.setAntiAlias(true);
line_paint.setColor(paintColor);
text_paint = new Paint();
text_paint.setAntiAlias(true);
text_paint.setColor(Color.BLUE);
text_paint.setTextSize(30);
countPaint = new Paint();
countPaint.setAntiAlias(true);
countPaint.setColor(Color.GREEN);
countPaint.setTextSize(60);
}
@Override
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
int num = pointMap.size();
if (num == 0)
{
clearDraw(canvas);
return;
}
for (Map.Entry<Integer, TouchPoint> entry : pointMap.entrySet())
{
TouchPoint point = entry.getValue();
canvas.drawLine(0, point.y, getWidth(), point.y, line_paint);
canvas.drawLine(point.x, 0, point.x, getHeight(), line_paint);
if (num == 1)
{
canvas.drawText(" (" + point.x + "," + point.y + ")", screenW / 2, screenH / 2, text_paint);
} else
{
canvas.drawText(String.valueOf(pointMap.size()), screenW / 2, screenH / 2, countPaint);
}
}
}
@Override
public boolean onTouchEvent(MotionEvent event)
{
int index = event.getActionIndex();
int id = event.getPointerId(index);
int pointerIndex = event.findPointerIndex(id);
int pointerCount = event.getPointerCount();
int historySize = event.getHistorySize();
switch (event.getActionMasked())
{
case MotionEvent.ACTION_POINTER_DOWN:
pointMap.put(pointerIndex, new TouchPoint(event.getX(pointerIndex), event.getY(pointerIndex)));
break;
case MotionEvent.ACTION_POINTER_UP:
pointMap.remove(pointerIndex);
break;
case MotionEvent.ACTION_MOVE:
for (int h = 0; h < historySize; h++)
{
for (int p = 0; p < pointerCount; p++)
{
pointMap.put(p, new TouchPoint(event.getHistoricalX(p, h), event.getHistoricalY(p, h)));
}
}
for (int p = 0; p < pointerCount; p++)
{
pointMap.put(p, new TouchPoint(event.getX(p), event.getY(p)));
}
break;
case MotionEvent.ACTION_DOWN:
pointMap.put(0, new TouchPoint(event.getX(pointerIndex), event.getY(pointerIndex)));
back_x1 = event.getX();
back_y1 = event.getY();
break;
case MotionEvent.ACTION_UP:
back_x2 = event.getX();
back_y2 = event.getY();
if (Math.abs(back_x1 - back_x2) > screenW / 2 && Math.abs(back_y1 - back_y2) > screenH / 2)
{
callOnClick();
}
pointMap.clear();
break;
default:
break;
}
if (event.getPointerCount() == 0) pointMap.clear();
invalidate();
return true;
}
class TouchPoint
{
public float x = 0;
public float y = 0;
TouchPoint(float x, float y)
{
this.x = x;
this.y = y;
}
}
void clearDraw(Canvas canvas)
{
Paint paint = new Paint();
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
canvas.drawPaint(paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
canvas.drawColor(Color.WHITE);
}
}
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