我修改了Android API的FingerPaint演示以支持多点触控。 除了以下问题外，它工作正常。在这种情况下：
Touch order: First Finger--Second Finger__________Lift order: Second Finger---First Finger
一切都很好。但。。。。。在这种情况下：
Touch order: First Finger--Second Finger__________Lift order: First Finger---SecondFinger
它从第一根手指离开屏幕的点到第二根手指在妈妈处的点画一条线。如果我以同样的方式使用三根或四根手指，也会发生同样的情况。我该如何解决这个问题？这是我的代码。（此代码依赖的所有类都在 Android API 的示例文件夹中）
public class FingerPaint extends GraphicsActivity {
int startx0,startx1,starty0,starty1,startx2,starty2,startx3,starty3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new MyView(this));
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(0xFFFF0000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(12);
mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
0.4f, 6, 3.5f);
mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
}
private Paint mPaint;
private MaskFilter mEmboss;
private MaskFilter mBlur;
public void colorChanged(int color) {
mPaint.setColor(color);
}
public class MyView extends View {
private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;
public MyView(Context c) {
super(c);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(0xFFAAAAAA);
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
canvas.drawPath(mPath, mPaint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
startx0 = (int) event.getX(0);
starty0 = (int) event.getY(0);
break;
case MotionEvent.ACTION_POINTER_DOWN:
try{
startx1 = (int) event.getX(1);
starty1 = (int) event.getY(1);
}catch(Exception e){}
try{
startx2 = (int) event.getX(2);
starty2 = (int) event.getY(2);
}catch(Exception e){}
try{
startx3 = (int) event.getX(3);
starty3 = (int) event.getY(3);
}catch(Exception e){}
break;
case MotionEvent.ACTION_MOVE:
try{
int x0 = (int) event.getX(0);
int y0 = (int) event.getY(0);
mCanvas.drawLine(startx0, starty0, x0, y0, mPaint);
startx0=x0;
starty0=y0;
invalidate();
}catch(Exception e){}
try{
int x1 = (int) event.getX(1);
int y1 = (int) event.getY(1);
mCanvas.drawLine(startx1, starty1, x1, y1, mPaint);
startx1=x1;
starty1=y1;
invalidate();
}catch(Exception e){}
try{
int x2 = (int) event.getX(2);
int y2 = (int) event.getY(2);
mCanvas.drawLine(startx2, starty2, x2, y2, mPaint);
startx2=x2;
starty2=y2;
invalidate();
}catch(Exception e){}
try{
int x3 = (int) event.getX(3);
int y3 = (int) event.getY(3);
mCanvas.drawLine(startx3, starty3, x3, y3, mPaint);
startx3=x3;
starty3=y3;
invalidate();
}catch(Exception e){}
break;
case MotionEvent.ACTION_POINTER_UP:
break;
case MotionEvent.ACTION_UP:
break;
}
return true;
}
}
private static final int COLOR_MENU_ID = Menu.FIRST;
private static final int EMBOSS_MENU_ID = Menu.FIRST + 1;
private static final int BLUR_MENU_ID = Menu.FIRST + 2;
private static final int ERASE_MENU_ID = Menu.FIRST + 3;
private static final int SRCATOP_MENU_ID = Menu.FIRST + 4;
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
menu.add(0, COLOR_MENU_ID, 0, "Color").setShortcut('3', 'c');
menu.add(0, EMBOSS_MENU_ID, 0, "Emboss").setShortcut('4', 's');
menu.add(0, BLUR_MENU_ID, 0, "Blur").setShortcut('5', 'z');
menu.add(0, ERASE_MENU_ID, 0, "Erase").setShortcut('5', 'z');
menu.add(0, SRCATOP_MENU_ID, 0, "SrcATop").setShortcut('5', 'z');
/**** Is this the mechanism to extend with filter effects?
Intent intent = new Intent(null, getIntent().getData());
intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
menu.addIntentOptions(
Menu.ALTERNATIVE, 0,
new ComponentName(this, NotesList.class),
null, intent, 0, null);
*****/
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
super.onPrepareOptionsMenu(menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
mPaint.setXfermode(null);
mPaint.setAlpha(0xFF);
switch (item.getItemId()) {
case EMBOSS_MENU_ID:
if (mPaint.getMaskFilter() != mEmboss) {
mPaint.setMaskFilter(mEmboss);
} else {
mPaint.setMaskFilter(null);
}
return true;
case BLUR_MENU_ID:
if (mPaint.getMaskFilter() != mBlur) {
mPaint.setMaskFilter(mBlur);
} else {
mPaint.setMaskFilter(null);
}
return true;
case ERASE_MENU_ID:
mPaint.setXfermode(new PorterDuffXfermode(
PorterDuff.Mode.CLEAR));
return true;
case SRCATOP_MENU_ID:
mPaint.setXfermode(new PorterDuffXfermode(
PorterDuff.Mode.SRC_ATOP));
mPaint.setAlpha(0x80);
return true;
}
return super.onOptionsItemSelected(item);
}
}
一旦你抬起第二根手指，就只有一根手指向下。这意味着event.getX(0)将包含剩余手指的数据 - 如果您抬起第一根手指，则第二根手指的数据将从getX(1)报告移动到getX(0)。
您不应该依靠触摸数组中的位置来识别手指，您应该使用 MotionEvent.getPointerId（int） 找出哪个手指处于哪个位置，并使用它来将事件映射到线条。