android用canvas画出线段和箭头

1、设置布局文件，添加2个控件，一个Button，一个ImageView

2、在MainAcitvity添加两个控件的全局变量，以及画图工具的全局变量 private Button btn_drawline; private ImageView iv_canvas; private Bitmap baseBitmap; private Canvas canvas; private Paint paint;

3、在oncreate()方法中初始化 Button控件和ImageView控件，并给Button添加按键监听按键监听中调用画图方法：// 初始化一个画笔，笔触宽度为5，颜色为红色 paint = new Paint(); paint.setStrokeWidth(1); paint.setColor(Color.RED);iv_canvas = (ImageView) findViewById(R.id.iv_canvas); btn_drawline.setOnClickListener(click); btn_drawline.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { drawTria((float) 300, (float) 100, (float) 100, (float) 400, 50, 10); } });

4、画线段和箭头的方法，处理芟镊圭薅箭头指向任何方向都能显示出来protected void drawTria(float fromX, float fromY, fl泠贾高框oat toX, float toY, int heigth, int bottom) { // heigth和bottom分别为三角形的高与底的一半,调节三角形大小 baseBitmap = Bitmap.createBitmap(iv_canvas.getWidth(), iv_canvas.getHeight(), Bitmap.Config.ARGB_8888); canvas = new Canvas(baseBitmap); canvas.drawColor(Color.YELLOW);// 设置底色 canvas.drawLine(fromX, fromY, toX, toY, paint); 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 - (heigth / juli * juliX); float dianY = toY - (heigth / juli * juliY); float dian2X = fromX + (heigth / juli * juliX); float dian2Y = fromY + (heigth / 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, paint); //显示图像 iv_canvas.setImageBitmap(baseBitmap); }

5、画出的箭头便随着线段的斜率而画出来了。线段的四个方向，以及线段平行X轴，平行Y轴的情况都能正常显示。

6、如果要画双向箭头，只需要再添加一个箭头议陬涸渎即可，调用以下方法：protected void drawTria烫喇霰嘴(float fromX, float fromY, float toX, float toY, int heigth, int bottom) { // heigth和bottom分别为三角形的高与底的一半,调节三角形大小 baseBitmap = Bitmap.createBitmap(iv_canvas.getWidth(), iv_canvas.getHeight(), Bitmap.Config.ARGB_8888); canvas = new Canvas(baseBitmap); canvas.drawColor(Color.YELLOW);// 设置底色 canvas.drawLine(fromX, fromY, toX, toY, paint); 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 - (heigth / juli * juliX); float dianY = toY - (heigth / juli * juliY); float dian2X = fromX + (heigth / juli * juliX); float dian2Y = fromY + (heigth / 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, paint); //起点的箭头 Path path2 = new Path(); path2.moveTo(fromX, fromY);// 此点为边形的起点 path2.lineTo(dian2X + (bottom / juli * juliY), dian2Y - (bottom / juli * juliX)); path2.lineTo(dian2X - (bottom / juli * juliY), dian2Y + (bottom / juli * juliX)); path2.close(); // 使这些点构成封闭的三边形 canvas.drawPath(path2, paint); //显示图像 iv_canvas.setImageBitmap(baseBitmap); }