我对Android很新，并且一直在玩Canvas。我试图画一个箭头，但我只是在绘制轴时没有运气，箭头都没有工作。
我搜索了一下，发现了一个Java示例，但Android没有GeneralPath或AffineTransform。
现在我的代码如下所示（箭头看起来像箭头）：
public class DrawableView extends View {
Context mContext;
private int centerX;
private int centerY;
private int radius;
private double arrLength;
private double arrHeading;
private int margin = 10;
public DrawableView(Context context) {
super(context);
mContext = context;
}
@Override
protected void onDraw(Canvas canvas) {
//Paint Background
Paint background = new Paint();
background.setColor(getResources().getColor(R.color.background);
canvas.drawRect(0, 0, getWidth(), getHeight(), background);
//Set vars for Arrow Paint
Paint paint = new Paint();
paint.setColor(getResources().getColor(R.color.arrowColor);
centerX = getWidth() / 2;
centerY = getHeight() / 2;
arrLength = radius - 10;
if(centerX < centerY)
radius = centerX - margin;
else
radius = centerY - margin;
//Draw Shaft
int[] xy = findArrowPos(arrLength, arrHeading);
canvas.drawLine(centerX, centerY, xy[0], xy[1], paint);
//Draw ArrowHead
//This is where I'm confused
}
private int[] findArrowPos(double length, double angle) {
int[] points = new int[2];
double theta = Math.toRadians(angle);
points[0] = centerX + (int) (length * Math.cos(theta));
points[1] = centerY + (int) (length * Math.sin(theta));
return points;
}
}
我已经看了下面的主题以获得指导： * http://www.java-forums.org/awt-swing/6241-how-u-rotate-arrow-mark-line-moves-accordingly.html * How to draw a directed arrow line in Java?
如何使用“Path myPath = new Path（）;”在哪里你可以给x和y位置用线创建一个三角形并填充它。你可以阅读它，这是我从某个地方采取的一个例子。
// create and draw triangles
// use a Path object to store the 3 line segments
// use .offset to draw in many locations
// note: this triangle is not centered at 0,0
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(2);
paint.setColor(Color.RED);
Path path = new Path();
path.moveTo(0, -10);
path.lineTo(5, 0);
path.lineTo(-5, 0);
path.close();
path.offset(10, 40);
canvas.drawPath(path, paint);
path.offset(50, 100);
canvas.drawPath(path, paint);
// offset is cumlative
// next draw displaces 50,100 from previous
path.offset(50, 100);
canvas.drawPath(path, paint);
我尝试这个代码它已经完美地工作：
switch (event.getAction())
{
case MotionEvent.ACTION_DOWN:
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
startPoint = new PointF(event.getX(), event.getY());
endPoint = new PointF();
invalidate();
break;
case MotionEvent.ACTION_MOVE:
float dx = Math.abs(x - mX);
System.out.println("action move");
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE)
{
// currentDrawingPath.path.quadTo(mX,mY,(x + mX)/2, (y + mY)/2);
}
mX = x;
mY = y;
endPoint.x = event.getX();
endPoint.y = event.getY();
isDrawing = true;
invalidate();
break;
case MotionEvent.ACTION_UP:
mPath.lineTo(mX, mY);
float deltaX = endPoint.x-startPoint.x;
float deltaY = endPoint.y-startPoint.y;
float frac = (float) 0.1;
float point_x_1 = startPoint.x + (float) ((1 - frac) * deltaX + frac * deltaY);
float point_y_1 = startPoint.y + (float) ((1 - frac) * deltaY - frac * deltaX);
float point_x_2 = endPoint.x;
float point_y_2 = endPoint.y;
float point_x_3 = startPoint.x + (float) ((1 - frac) * deltaX - frac * deltaY);
float point_y_3 = startPoint.y + (float) ((1 - frac) * deltaY + frac * deltaX);
mPath.moveTo(point_x_1, point_y_1);
mPath.lineTo(point_x_2, point_y_2);
mPath.lineTo(point_x_3, point_y_3);
mPath.lineTo(point_x_1, point_y_1);
mPath.lineTo(point_x_1, point_y_1);
mCanvas.drawPath(mPath, ppaint);
endPoint.x = event.getX();
endPoint.y = event.getY();
isDrawing = false;
invalidate();
break;
default:
break;
}
我的箭头绘图代码，也许它对某些人有用：
/**
* Draw an arrow
* change internal radius and angle to change appearance
* - angle : angle in degrees of the arrows legs
* - radius : length of the arrows legs
* @author Steven Roelants 2017
*
* @param paint
* @param canvas
* @param from_x
* @param from_y
* @param to_x
* @param to_y
*/
private void drawArrow(Paint paint, Canvas canvas, float from_x, float from_y, float to_x, float to_y)
{
float angle,anglerad, radius, lineangle;
//values to change for other appearance *CHANGE THESE FOR OTHER SIZE ARROWHEADS*
radius=10;
angle=15;
//some angle calculations
anglerad= (float) (PI*angle/180.0f);
lineangle= (float) (atan2(to_y-from_y,to_x-from_x));
//tha line
canvas.drawLine(from_x,from_y,to_x,to_y,paint);
//tha triangle
Path path = new Path();
path.setFillType(Path.FillType.EVEN_ODD);
path.moveTo(to_x, to_y);
path.lineTo((float)(to_x-radius*cos(lineangle - (anglerad / 2.0))),
(float)(to_y-radius*sin(lineangle - (anglerad / 2.0))));
path.lineTo((float)(to_x-radius*cos(lineangle + (anglerad / 2.0))),
(float)(to_y-radius*sin(lineangle + (anglerad / 2.0))));
path.close();
canvas.drawPath(path, paint);
}
我一直有同样的问题，我需要一个箭头指向某个方向。在使用绘图算法后，我认为最简单的方法是使用位图并简单地使用矩阵来旋转它，例如
ImageView image = (ImageView) findViewById(R.id.bitmap_image);
Bitmap bMap = BitmapFactory.decodeResource(getResources(), R.drawable.test);
Matrix mat = new Matrix();
mat.postRotate(90);
Bitmap bMapRotate = Bitmap.createBitmap(bMap, 0, 0, bMap.getWidth(), bMap.getHeight(), mat, true);
image.setImageBitmap(bMapRotate);
那么你的位图可以是你喜欢的任何花哨的箭头。
如果您正在寻找在一秒钟内绘制数千个箭头的解决方案，并使用固定长度的头部线条，请尝试此功能（仅绘制箭头）：
private void fillArrow(Paint paint, Canvas canvas, float x0, float y0, float x1, float y1) {
paint.setStyle(Paint.Style.STROKE);
int arrowHeadLenght = 10;
int arrowHeadAngle = 45;
float[] linePts = new float[] {x1 - arrowHeadLenght, y1, x1, y1};
float[] linePts2 = new float[] {x1, y1, x1, y1 + arrowHeadLenght};
Matrix rotateMat = new Matrix();
//get the center of the line
float centerX = x1;
float centerY = y1;
//set the angle
double angle = Math.atan2(y1 - y0, x1 - x0) * 180 / Math.PI + arrowHeadAngle;
//rotate the matrix around the center
rotateMat.setRotate((float) angle, centerX, centerY);
rotateMat.mapPoints(linePts);
rotateMat.mapPoints(linePts2);
canvas.drawLine(linePts [0], linePts [1], linePts [2], linePts [3], paint);
canvas.drawLine(linePts2 [0], linePts2 [1], linePts2 [2], linePts2 [3], paint);
}
基于https://gamedev.stackexchange.com/questions/44456/drawing-lines-on-android-with-matrix
使用如下的Path并相应调整坐标：
// Construct a wedge-shaped path
Path mPath = new Path();
mPath.moveTo(0, -50);
mPath.lineTo(-20, 60);
mPath.lineTo(0, 50);
mPath.lineTo(20, 60);
mPath.close();