Android: Drawing an arc inside a circle

问题

I'm trying to draw an arc inside a circle to represent the temperature, but I'm having a difficult time achieving that. During my search I found those solutions

This one I couldn't understand what is the scale method for, and is drawing more than one arch, which confused me a bit

This post gave it a fixed size where I need the size to be controlled by the custom view in my XML layout

From here I understood the concept the degrees but I didn't understand how to determine the oval size

What i reached so far

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    int startTop = 0;
    int startLeft = 0;
    int endBottom = getHeight() / 2;
    int endRight = endBottom;// This makes an equal square.

    int centerX = getWidth() / 2;
    int centerY = getHeight() / 2;

    int upperEdgeX = (int) (centerX + getWidth() / 2 * Math.cos(270 * Math.PI / 180));
    int upperEdgeY = (int) (centerY + getWidth() / 2 * Math.sin(270 * Math.PI / 180));

    int bottomEdgeX = (int) (centerX + getWidth() / 2 * Math.cos(90 * Math.PI / 180));
    int bottomEdgeY = (int) (centerY + getWidth() / 2 * Math.sin(90 * Math.PI / 180));

    int leftEdgeX = (int) (centerX + getWidth() / 2 * Math.cos(180 * Math.PI / 180));
    int leftEdgeY = (int) (centerY + getWidth() / 2 * Math.sin(180 * Math.PI / 180));

    int rightEdgeX = (int) (centerX + getWidth() / 2 * Math.cos(0 * Math.PI / 180));
    int rightEdgeY = (int) (centerY + getWidth() / 2 * Math.sin(0 * Math.PI / 180));

    RectF rect = new RectF(startTop, startLeft, endRight, endBottom);
    canvas.drawCircle(centerX, centerY, getWidth() / 2, mBasePaint);


    canvas.drawCircle(centerX, centerY, getWidth() / 3, mCenterPaint); // White circle
}

UPDATE: I need my view to be like a Donut Pie chart where the middle will hold the degree

UPDATE 2:

I'm trying to have something like this

回答1:

The following custom View draws two arcs connecting to form a circle as well as an inner circle.

Moreover, I let it fill the rectangle used for drawing the arc and use a yellow background for the View, the activity background is dark. (These additional features are meant for getting a better impression of how drawing a circle / an arc works, they can help with debugging.)

The custom View:

public class MySimpleView extends View{

private static final int STROKE_WIDTH = 20;
private Paint mBasePaint, mDegreesPaint, mCenterPaint, mRectPaint;
private RectF mRect;
private int centerX, centerY, radius;

public MySimpleView(Context context) {
    super(context);
    init();
}

public MySimpleView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
}

public MySimpleView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
}

private void init()
{
    mRectPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mRectPaint.setColor(ContextCompat.getColor(getContext(), R.color.magenta));
    mRectPaint.setStyle(Paint.Style.FILL);

    mCenterPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mCenterPaint.setColor(ContextCompat.getColor(getContext(), R.color.white));
    mCenterPaint.setStyle(Paint.Style.FILL);

    mBasePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mBasePaint.setStyle(Paint.Style.STROKE);
    mBasePaint.setStrokeWidth(STROKE_WIDTH);
    mBasePaint.setColor(ContextCompat.getColor(getContext(), R.color.blue));

    mDegreesPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mDegreesPaint.setStyle(Paint.Style.STROKE);
    mDegreesPaint.setStrokeWidth(STROKE_WIDTH);
    mDegreesPaint.setColor(ContextCompat.getColor(getContext(), R.color.green));

}


@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    // getHeight() is not reliable, use getMeasuredHeight() on first run:
    // Note: mRect will also be null after a configuration change,
    // so in this case the new measured height and width values will be used:
    if (mRect == null)
    {
        // take the minimum of width and height here to be on he safe side:
        centerX = getMeasuredWidth()/ 2;
        centerY = getMeasuredHeight()/ 2;
        radius = Math.min(centerX,centerY);

        // mRect will define the drawing space for drawArc()
        // We have to take into account the STROKE_WIDTH with drawArc() as well as drawCircle():
        // circles as well as arcs are drawn 50% outside of the bounds defined by the radius (radius for arcs is calculated from the rectangle mRect).
        // So if mRect is too large, the lines will not fit into the View
        int startTop = STROKE_WIDTH / 2;
        int startLeft = startTop;

        int endBottom = 2 * radius - startTop;
        int endRight = endBottom;

        mRect = new RectF(startTop, startLeft, endRight, endBottom);
    }

    // just to show the rectangle bounds:
    canvas.drawRect(mRect, mRectPaint);

    // subtract half the stroke width from radius so the blue circle fits inside the View
    canvas.drawCircle(centerX, centerY, radius - STROKE_WIDTH / 2, mBasePaint);
    // Or draw arc from degree 192 to degree 90 like this ( 258 = (360 - 192) + 90:
    // canvas.drawArc(mRect, 192, 258, false, mBasePaint);

    // draw an arc from 90 degrees to 192 degrees (102 = 192 - 90)
    // Note that these degrees are not like mathematical degrees:
    // they are mirrored along the y-axis and so incremented clockwise (zero degrees is always on the right hand side of the x-axis)
    canvas.drawArc(mRect, 90, 102, false, mDegreesPaint);

    // subtract stroke width from radius so the white circle does not cover the blue circle/ arc
    canvas.drawCircle(centerX, centerY, radius - STROKE_WIDTH, mCenterPaint);
}
}

来源：https://stackoverflow.com/questions/39206733/android-drawing-an-arc-inside-a-circle