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，处理箭头指向任何方向都能显示出来
protected void drawTria(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);
//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即可，调用以下方法：
protected void drawTria(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);
}
