DashedLineView

attrs_dashedlineview.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <declare-styleable name="DashedLineView">
    <attr format="color"
        name="dlw_color"/>
    <attr format="float"
        name="dlw_dash"/>
    <attr format="float"
        name="dlw_gap"/>
    <attr format="float"
        name="dlw_phase"/>
  </declare-styleable>
</resources>

DashedLineView.java

public class DashedLineView extends View {
  private static final int DEFAULT_COLOR = Color.BLACK;
  private static final float DEFAULT_DASH = 4f;
  private static final float DEFAULT_GAP = 2f;
  private static final float DEFAULT_PHASE = 0f;

  private final Paint paint = new Paint();
  private final Path path = new Path();

  private float dash;
  private float gap;
  private float phase;

  public DashedLineView(Context context) {
    this(context, null);
  }

  public DashedLineView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public DashedLineView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    init(attrs);
  }

  private void init(@Nullable AttributeSet attrs) {
    paint.setStyle(Paint.Style.STROKE);

    TypedArray typedArray = getContext().obtainStyledAttributes(attrs, R.styleable.DashedLineView);
    paint.setColor(typedArray.getColor(R.styleable.DashedLineView_dlw_color, DEFAULT_COLOR));
    dash = typedArray.getFloat(R.styleable.DashedLineView_dlw_dash, DEFAULT_DASH);
    gap = typedArray.getFloat(R.styleable.DashedLineView_dlw_gap, DEFAULT_GAP);
    phase = typedArray.getFloat(R.styleable.DashedLineView_dlw_phase, DEFAULT_PHASE);
    typedArray.recycle();

    paint.setPathEffect(new DashPathEffect(new float[] { dash, gap }, phase));
  }

  @Override protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    path.moveTo(0, 0);

    int measuredHeight = getMeasuredHeight();
    int measuredWidth = getMeasuredWidth();
    if (measuredHeight <= measuredWidth) {
      // horizontal
      path.lineTo(measuredWidth, 0);
    } else {
      // vertical
      path.lineTo(0, measuredHeight);
    }
    canvas.drawPath(path, paint);
  }

  public void setColor(@ColorInt int color) {
    paint.setColor(color);
    invalidate();
  }

  public void setColorResource(@ColorRes int color) {
    paint.setColor(ContextCompat.getColor(getContext(), color));
    invalidate();
  }

  public void setDash(float dash) {
    this.dash = dash;
    updateDashPathEffect();
  }

  public void setGap(float gap) {
    this.gap = gap;
    updateDashPathEffect();
  }

  public void setPhase(float phase) {
    this.phase = phase;
    updateDashPathEffect();
  }

  public void setDashedLine(float dash, float gap, float phase) {
    this.dash = dash;
    this.gap = gap;
    this.phase = phase;
    updateDashPathEffect();
  }

  private void updateDashPathEffect() {
    paint.setPathEffect(new DashPathEffect(new float[] { dash, gap }, phase));
    invalidate();
  }
}