Android Canvas绘制带箭头的直线

先看下效果图：

在这里插入图片描述

下面我们直接看代码

我自定义了一个View，代码如下：

package com.davis.drawtrangle;import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;import java.util.ArrayList;
import java.util.List;public class DrawView extends View {private List<PointBean> pointLists = new ArrayList<PointBean>();private PointBean pointBean = new PointBean(-1, -1, -1, -1);private static int height = 30;private static int bottom = 10;private Paint paint = new Paint(){{setColor(Color.RED);setAntiAlias(true);setStrokeWidth(4.0f);}};public DrawView(Context context) {super(context);}public DrawView(Context context, @Nullable AttributeSet attrs) {super(context, attrs);}public DrawView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}public void clear(){if(pointBean != null){pointBean.setStartX(-1);pointBean.setStartY(-1);pointBean.setEndX(-1);pointBean.setEndY(-1);}if(pointLists != null && pointLists.size() > 0){pointLists.clear();}invalidate();}@Overrideprotected void onDraw(Canvas canvas) {//super.onDraw(canvas);if(pointLists != null && pointLists.size() > 0){for(int i=0;i<pointLists.size();i++){PointBean pb = pointLists.get(i);canvas.drawLine(pb.getStartX(), pb.getStartY(), pb.getEndX(), pb.getEndY(), paint);drawTrangle(canvas, paint, pb.getStartX(), pb.getStartY(), pb.getEndX(), pb.getEndY(), height, bottom);}}if(pointBean != null && pointBean.getStartX() != -1&& pointBean.getStartY() != -1 && pointBean.getEndX() != -1&& pointBean.getEndY() != -1){canvas.drawLine(pointBean.getStartX(), pointBean.getStartY(), pointBean.getEndX(), pointBean.getEndY(), paint);drawTrangle(canvas, paint, pointBean.getStartX(), pointBean.getStartY(), pointBean.getEndX(), pointBean.getEndY(), height, bottom);}}/*** 绘制三角* @param canvas* @param fromX* @param fromY* @param toX* @param toY* @param height* @param bottom*/private void drawTrangle(Canvas canvas, Paint paintLine, float fromX, float fromY, float toX, float toY, int height, int bottom){try{float juli = (float) Math.sqrt((toX - fromX) * (toX - fromX)+ (toY - fromY) * (toY - fromY));// 获取线段距离float juliX = toX - fromX;// 有正负，不要取绝对值float juliY = toY - fromY;// 有正负，不要取绝对值float dianX = toX - (height / juli * juliX);float dianY = toY - (height / juli * juliY);float dian2X = fromX + (height / juli * juliX);float dian2Y = fromY + (height / juli * juliY);//终点的箭头Path path = new Path();path.moveTo(toX, toY);// 此点为三边形的起点path.lineTo(dianX + (bottom / juli * juliY), dianY- (bottom / juli * juliX));path.lineTo(dianX - (bottom / juli * juliY), dianY+ (bottom / juli * juliX));path.close(); // 使这些点构成封闭的三边形canvas.drawPath(path, paintLine);}catch (Exception ex){ex.printStackTrace();}}@Overridepublic boolean onTouchEvent(MotionEvent event) {int action = event.getAction();switch (action){case MotionEvent.ACTION_DOWN:onActionDown(event);break;case MotionEvent.ACTION_MOVE:onActionMove(event);break;case MotionEvent.ACTION_UP:onActionUp(event);break;}return true;//return super.onTouchEvent(event);}private void onActionDown(MotionEvent event){try {if(pointBean == null){pointBean = new PointBean(-1, -1, -1, -1);}pointBean.setStartX(event.getX());pointBean.setStartY(event.getY());}catch (Exception ex){ex.printStackTrace();}invalidate();}private void onActionMove(MotionEvent event){try{if(pointBean != null){pointBean.setEndX(event.getX());pointBean.setEndY(event.getY());}}catch (Exception ex){ex.printStackTrace();}invalidate();}private void onActionUp(MotionEvent event){try {if(pointBean != null){pointBean.setEndX(event.getX());pointBean.setEndY(event.getY());PointBean pb = new PointBean();pb.setStartX(pointBean.getStartX());pb.setStartY(pointBean.getStartY());pb.setEndX(pointBean.getEndX());pb.setEndY(pointBean.getEndY());pointLists.add(pb);pointBean.setStartX(-1);pointBean.setStartY(-1);pointBean.setEndX(-1);pointBean.setEndY(-1);}}catch (Exception ex){ex.printStackTrace();}invalidate();}}