机器人：寻找与内外半径

Question

一个drawArc（）方法我有以下定制视图：

这我已通过使用画布drawArc()方法来实现。然而，用这种方法我不能限制弧的内半径。

我想什么有是这样的：

那里只有外圈离开。

我需要的是一个drawArc()函数，我可以设置弧的内半径。任何人有一个想法如何做到这一点？

（顺便说一下，覆盖内部区域不起作用，因为它需要透明。在绘制红色和蓝色圆锥体后用Color.TRANSPARENT绘制内部圆圈并不会除去旧颜色，顶部，这是透明的，通过它我仍然可以看到红色和蓝色）

Answer 1

您可以使用名为“Clear”的PorterDuff xfermode在内部区域上绘画。这会擦除像素。

Answer 2

你可以这样做：

Paint paint = new Paint(); 
    final RectF rect = new RectF(); 
    //Example values 
    rect.set(mWidth/2- mRadius, mHeight/2 - mRadius, mWidth/2 + mRadius, mHeight/2 + mRadius); 
    paint.setColor(Color.GREEN); 
    paint.setStrokeWidth(20); 
    paint.setAntiAlias(true); 
    paint.setStrokeCap(Paint.Cap.ROUND); 
    paint.setStyle(Paint.Style.STROKE); 
    canvas.drawArc(rect, -90, 360, false, paint); 

的关键是paint.setStyle(Paint.Style.STROKE);，它裁剪弧与您在setStrokeWidth定义行程中心（在示例绘制mRadius和20像素厚的半径的圆弧）。

希望它有帮助！

Answer 3

private static final float CIRCLE_LIMIT = 359.9999f; 
/** 
* Draws a thick arc between the defined angles, see {@link Canvas#drawArc} for more. 
* This method is equivalent to 
* <pre><code> 
* float rMid = (rInn + rOut)/2; 
* paint.setStyle(Style.STROKE); // there's nothing to fill 
* paint.setStrokeWidth(rOut - rInn); // thickness 
* canvas.drawArc(new RectF(cx - rMid, cy - rMid, cx + rMid, cy + rMid), startAngle, sweepAngle, false, paint); 
* </code></pre> 
* but supports different fill and stroke paints. 
* 
* @param canvas 
* @param cx horizontal middle point of the oval 
* @param cy vertical middle point of the oval 
* @param rInn inner radius of the arc segment 
* @param rOut outer radius of the arc segment 
* @param startAngle see {@link Canvas#drawArc} 
* @param sweepAngle see {@link Canvas#drawArc}, capped at &plusmn;360 
* @param fill filling paint, can be <code>null</code> 
* @param stroke stroke paint, can be <code>null</code> 
* @see Canvas#drawArc 
*/ 
public static void drawArcSegment(Canvas canvas, float cx, float cy, float rInn, float rOut, float startAngle, 
     float sweepAngle, Paint fill, Paint stroke) { 
    if (sweepAngle > CIRCLE_LIMIT) { 
     sweepAngle = CIRCLE_LIMIT; 
    } 
    if (sweepAngle < -CIRCLE_LIMIT) { 
     sweepAngle = -CIRCLE_LIMIT; 
    } 

    RectF outerRect = new RectF(cx - rOut, cy - rOut, cx + rOut, cy + rOut); 
    RectF innerRect = new RectF(cx - rInn, cy - rInn, cx + rInn, cy + rInn); 

    Path segmentPath = new Path(); 
    double start = toRadians(startAngle); 
    segmentPath.moveTo((float)(cx + rInn * cos(start)), (float)(cy + rInn * sin(start))); 
    segmentPath.lineTo((float)(cx + rOut * cos(start)), (float)(cy + rOut * sin(start))); 
    segmentPath.arcTo(outerRect, startAngle, sweepAngle); 
    double end = toRadians(startAngle + sweepAngle); 
    segmentPath.lineTo((float)(cx + rInn * cos(end)), (float)(cy + rInn * sin(end))); 
    segmentPath.arcTo(innerRect, startAngle + sweepAngle, -sweepAngle); 
    if (fill != null) { 
     canvas.drawPath(segmentPath, fill); 
    } 
    if (stroke != null) { 
     canvas.drawPath(segmentPath, stroke); 
    } 
} 

可以通过复制rInn和rOut为x和y方向扩展到椭圆弧。

也没问题的一部分，但在段的中间画一个文本：

textPaint.setTextAlign(Align.CENTER); 
Path midway = new Path(); 
float r = (rIn + rOut)/2; 
RectF segment = new RectF(cx - r, cy - r, cx + r, cy + r); 
midway.addArc(segment, startAngle, sweepAngle); 
canvas.drawTextOnPath("label", midway, 0, 0, textPaint); 

Answer 4

你可以尝试以下ShapeDrawable

<?xml version="1.0" encoding="utf-8"?> 
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" > 
<item> 
    <shape android:shape="oval" > 
     <size 
      android:height="56dp" 
      android:width="56dp" /> 

     <stroke 
      android:width="10dp" 
      android:color="#0000ff" /> 
    </shape> 
</item> 
<item> 
    <shape android:shape="oval" > 
     <size 
      android:height="24dp" 
      android:width="25dp" /> 

     <stroke 
      android:dashGap="10dp" 
      android:dashWidth="10dp" 
      android:width="10dp" 
      android:color="#FF0000" /> 
    </shape> 
</item>