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Android觸摸事件如何實現(xiàn)筆觸畫布詳解

更新時間：2018年10月31日 08:41:10 作者：張風(fēng)捷特烈

這篇文章主要給大家介紹了關(guān)于Android觸摸事件如何實現(xiàn)筆觸畫布的相關(guān)資料，文中通過示例代碼介紹的非常詳細(xì)，對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

前言

任何View都有觸摸事件,經(jīng)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(diǎn)，下面話不多說了，來一起看看詳細(xì)的介紹吧

本篇分為三個等級：一覽圖：

直線

曲線

筆觸

LEVEL1:基礎(chǔ)實現(xiàn)

在Activity中通過一個全屏的Bitmap創(chuàng)建的Canvas繪制

為ImageView添加觸摸事件監(jiān)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(chuàng)建畫布

//獲取屏幕尺寸
Point point = new Point();
getWindowManager().getDefaultDisplay().getSize(point);

//創(chuàng)建一個和屏幕一樣大的Bitmap
Bitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888);
//創(chuàng)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(jiān)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(diǎn)位
   downY = upY;
   downX = upX;
   break;
  case MotionEvent.ACTION_UP:
   //抬起點(diǎn)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(jù)繪制的速度動態(tài)改變畫筆粗細(xì)

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(zhuǎn)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(xiàn)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(shè)置副本圖片到ImageView
mIdIvShow.setImageBitmap(mNewBitmap);