前言

任何View都有触摸事件,经常在自定义控件时重写setOnTouchListener

本篇通过手绘图片来讲述这个知识点，下面话不多说了，来一起看看详细的介绍吧

本篇分为三个等级：一览图：

直线

曲线

笔触

LEVEL1:基础实现

在Activity中通过一个全屏的Bitmap创建的Canvas绘制

为ImageView添加触摸事件监听。

1.成员变量

ImageView mIdIvShow;

float downX = 0;

float downY = 0;

float upX = 0;

float upY = 0;

private Canvas mCanvas;

private Paint mPaint;

2.创建画布

//获取屏幕尺寸

Point point = new Point();

getWindowManager().getDefaultDisplay().getSize(point);

//创建一个和屏幕一样大的Bitmap

Bitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888);

//创建Canvas对象

mCanvas = new Canvas(bitmap);

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

mPaint.setStrokeWidth(10);

mPaint.setColor(Color.RED);

//将bitmap用ImageView展示

mIdIvShow.setImageBitmap(bitmap);

3.监听事件

mIdIvShow.setOnTouchListener((v, event) -> {

switch (event.getAction()) {

case MotionEvent.ACTION_DOWN:

downX = event.getX();

downY = event.getY();

L.d("按下:(" + downX + "," + downY + ")" + L.l());

break;

case MotionEvent.ACTION_CANCEL:

break;

case MotionEvent.ACTION_MOVE:

break;

case MotionEvent.ACTION_UP:

upX = event.getX();

upY = event.getY();

L.d("抬起:(" + upX + "," + upY + ")" + L.l());

mCanvas.drawLine(downX, downY, upX, upY, mPaint);

mIdIvShow.invalidate();//更新视图

break;

}

return true;

});

}

升级版：LEVER2

mIdIvShow.setOnTouchListener((v, event) -> {

switch (event.getAction()) {

case MotionEvent.ACTION_DOWN:

downX = event.getX();

downY = event.getY();

break;

case MotionEvent.ACTION_CANCEL:

break;

case MotionEvent.ACTION_MOVE:

upX = event.getX();

upY = event.getY();

mCanvas.drawLine(downX, downY, upX, upY, mPaint);

mIdIvShow.invalidate();

//更新点位

downY = upY;

downX = upX;

break;

case MotionEvent.ACTION_UP:

//抬起点Y>1100,清除笔迹

if (upY > 1100) {

Paint paint = new Paint();

paint.setColor(Color.WHITE);

mCanvas.drawRect(0, 0, mPoint.x, mPoint.y, paint);

}

break;

}

return true;

});

再升级版：LEVER3

笔触根据绘制的速度动态改变画笔粗细

float movingX = 0;

float movingY = 0;

private long lastTimestamp = 0L;//最后一次的时间戳

mIdIvShow.setOnTouchListener((view, event) -> {

switch (event.getAction()) {

case MotionEvent.ACTION_DOWN:

lastTimestamp = System.currentTimeMillis();

downX = event.getX();

downY = event.getY();

break;

case MotionEvent.ACTION_CANCEL:

break;

case MotionEvent.ACTION_MOVE:

movingX = event.getX();

movingY = event.getY();

long curTimestamp = System.currentTimeMillis();

//计算时间差

long detaT = curTimestamp - lastTimestamp;

//计算距离差

float detaS = Logic.disPos2d(movingX, movingY, downX, downY);

//由于速度是 px/ms

double v = detaS / detaT;

//速度转化为画笔宽度的等式

float width = 14/(float)v;

L.d(width + L.l());

//限制极值情况

if ((width > 0) && width < 30) {

mPaint.setStrokeWidth(width);

}

mCanvas.drawLine(downX, downY, movingX, movingY, mPaint);

mIdIvShow.invalidate();

downX = movingX;

downY = movingY;

lastTimestamp = curTimestamp;//更新时间

movePos.add(new PointF(event.getX(), event.getY()));

break;

}

return true;

});

拓展

1.其中可以改变求宽度的等式实现不同的笔触:如

float width = (float) Math.log10(v) * 40;

2.在图片上绘画

//图片原型

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.iv_500x400);

//图片副本

Bitmap mNewBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());

//用副本生成Canvas

mCanvas = new Canvas(mNewBitmap);

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

mPaint.setStrokeCap(Paint.Cap.ROUND);//直线圆头

mCanvas.drawBitmap(bitmap, new Matrix(), mPaint);

mPaint.setStrokeWidth(10);

mPaint.setColor(Color.parseColor("#88164BE6"));

//设置副本图片到ImageView

mIdIvShow.setImageBitmap(mNewBitmap);

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对脚本之家的支持。