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前言
任何View都有觸摸事件,經常在自定義控件時重寫setOnTouchListener
本篇通過手繪圖片來講述這個知識點，下面話不多說了，來一起看看詳細的介紹吧
本篇分為三個等級：一覽圖：
直線
曲線
筆觸
LEVEL1:基礎實現
在Activity中通過一個全屏的Bitmap創建的Canvas繪制
為ImageView添加觸摸事件監聽。
1.成員變量
ImageView mIdIvShow; float downX = 0; float downY = 0; float upX = 0; float upY = 0; private Canvas mCanvas; private Paint mPaint;
2.創建畫布
//獲取屏幕尺寸 Point point = new Point(); getWindowManager().getDefaultDisplay().getSize(point); //創建一個和屏幕一樣大的Bitmap Bitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888); //創建Canvas對象 mCanvas = new Canvas(bitmap); mPaint = new Paint(Paint.ANTI_ALIAS_FLAG); mPaint.setStrokeWidth(10); mPaint.setColor(Color.RED); //將bitmap用ImageView展示 mIdIvShow.setImageBitmap(bitmap);
3.監聽事件
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();//更新視圖
break;
}
return true;
});
}
升級版：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();
//更新點位
downY = upY;
downX = upX;
break;
case MotionEvent.ACTION_UP:
//抬起點Y>1100,清除筆跡
if (upY > 1100) {
Paint paint = new Paint();
paint.setColor(Color.WHITE);
mCanvas.drawRect(0, 0, mPoint.x, mPoint.y, paint);
}
break;
}
return true;
});
再升級版：LEVER3
筆觸根據繪制的速度動態改變畫筆粗細
float movingX = 0; float movingY = 0; private long lastTimestamp = 0L;//最后一次的時間戳
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();
//計算時間差
long detaT = curTimestamp - lastTimestamp;
//計算距離差
float detaS = Logic.disPos2d(movingX, movingY, downX, downY);
//由于速度是 px/ms
double v = detaS / detaT;
//速度轉化為畫筆寬度的等式
float width = 14/(float)v;
L.d(width + L.l());
//限制極值情況
if ((width > 0) && width < 30) {
mPaint.setStrokeWidth(width);
}
mCanvas.drawLine(downX, downY, movingX, movingY, mPaint);
mIdIvShow.invalidate();
downX = movingX;
downY = movingY;
lastTimestamp = curTimestamp;//更新時間
movePos.add(new PointF(event.getX(), event.getY()));
break;
}
return true;
});
拓展
1.其中可以改變求寬度的等式實現不同的筆觸:如
float width = (float) Math.log10(v) * 40;
2.在圖片上繪畫
//圖片原型
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.iv_500x400);
//圖片副本
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);//直線圓頭
mCanvas.drawBitmap(bitmap, new Matrix(), mPaint);
mPaint.setStrokeWidth(10);
mPaint.setColor(Color.parseColor("#88164BE6"));
//設置副本圖片到ImageView
mIdIvShow.setImageBitmap(mNewBitmap);
總結
以上就是這篇文章的全部內容了，希望本文的內容對大家的學習或者工作具有一定的參考學習價值，如果有疑問大家可以留言交流，謝謝大家對億速云的支持。
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