The Android Developer’s Cookbook: Building Applications with the Android SDK, Second Edition (2013)

package com.cookbook.advance.customcomponent;

import android.content.Context;
import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Matrix;import android.graphics.Paint;import android.graphics.RectF;import android.graphics.Shader;import android.graphics.SweepGradient;import android.util.AttributeSet;
import android.util.Log;
import android.widget.Button;

public class MyButton extends Button {
private Paint mTextPaint, mPaint;
private String mText;
private int mAscent;
private Shader mShader;
private Matrix mMatrix = new Matrix();
private float mStart;
private float mSweep;
private float mRotate;
private static final float SWEEP_INC = 2;
private static final float START_INC = 15;

public MyButton(Context context) {
super(context);
initLabelView();
}

public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
initLabelView();
}

private final void initLabelView() {
mTextPaint = new Paint();
mTextPaint.setAntiAlias(true);
mTextPaint.setTextSize(16);
mTextPaint.setColor(0xFF000000);
setPadding(15, 15, 15, 15);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setStrokeWidth(4);
mPaint.setAntiAlias(true);
mPaint.setStyle(Paint.Style.STROKE);
mShader = new SweepGradient(this.getMeasuredWidth()/2,
this.getMeasuredHeight()/2,
new int[] { Color.GREEN,
Color.RED,
Color.CYAN,Color.DKGRAY },
null);
mPaint.setShader(mShader);
}

public void setText(String text) {
mText = text;
requestLayout();
invalidate();
}

public void setTextSize(int size) {
mTextPaint.setTextSize(size);
requestLayout();
invalidate();
}

public void setTextColor(int color) {
mTextPaint.setColor(color);
invalidate();
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
setMeasuredDimension(measureWidth(widthMeasureSpec),
measureHeight(heightMeasureSpec));
}

private int measureWidth(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);

if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text
result = (int) mTextPaint.measureText(mText)
+ getPaddingLeft()
+ getPaddingRight();
if (specMode == MeasureSpec.AT_MOST) {
result = Math.min(result, specSize);
}
}

return result;
}

private int measureHeight(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);

mAscent = (int) mTextPaint.ascent();
if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text (beware: ascent is a negative number)
result = (int) (-mAscent + mTextPaint.descent())
+ getPaddingTop() + getPaddingBottom();
if (specMode == MeasureSpec.AT_MOST) {
Log.v("Measure Height", "At most Height:"+specSize);
result = Math.min(result, specSize);
}
}
return result;
}

private void drawArcs(Canvas canvas, RectF oval, boolean useCenter,
Paint paint) {
canvas.drawArc(oval, mStart, mSweep, useCenter, paint);
}

@Override protected void onDraw(Canvas canvas) {
mMatrix.setRotate(mRotate, this.getMeasuredWidth()/2,
this.getMeasuredHeight()/2);
mShader.setLocalMatrix(mMatrix);
mRotate += 3;
if (mRotate >= 360) {
mRotate = 0;
}
RectF drawRect = new RectF();
drawRect.set(this.getWidth()-mTextPaint.measureText(mText),
(this.getHeight()-mTextPaint.getTextSize())/2,
mTextPaint.measureText(mText),
this.getHeight()-(this.getHeight()-mTextPaint.getTextSize())/2);
drawArcs(canvas, drawRect, false, mPaint);
mSweep += SWEEP_INC;
if (mSweep > 360) {
mSweep -= 360;
mStart += START_INC;
if (mStart >= 360) {
mStart -= 360;
}
}
if(mSweep >180){
canvas.drawText(mText, getPaddingLeft(),
getPaddingTop() -mAscent, mTextPaint);
}
invalidate();
}
}