android spinner 下拉框宽度设置 android 自定义下拉按钮

1、可以设置多种颜色。
2、可以显示多种状态（LOADING、SUCCESS、ERROR，其实远不止这几种）
3、可以控制是否显示箭头

相关准备工作

知识点：

1.Canvas里面相关方法
2.drawArc()画圆弧的方法
3.drawPath()画路径的方法
4.属性动画使用

结果的钩钩或者那个叉叉还有那个箭头都是使用drawPath()来完成的。

在onDraw里面对应有四个相关的方法：

1.drawArc(Canvas canvas)：画对应的进度
2.drawTriangle(Canvas c, float startAngle, float sweepAngle)：画箭头
3.drawHook(Canvas canvas)：画钩钩
4.drawError（Canvas canvas）：画叉叉

三个动画控制：

两个来控制进度条的 startAngle和sweepAngle,一个用来控制画钩钩或者画叉叉的时候的渐变效果！

相关代码

三支画笔

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeCap(Cap.ROUND);
    mPaint.setStrokeWidth(mBorderWidth);
    mPaint.setColor(mColors[mCurrentColorIndex]);

    mHookPaint = new Paint(mPaint);
    mArrowPaint = new Paint(mPaint);

三个动画

private void setupAnimations() {
    mObjectAnimatorAngle = ObjectAnimator.ofFloat(this, mAngleProperty, 360f);
    mObjectAnimatorAngle.setInterpolator(ANGLE_INTERPOLATOR);
    mObjectAnimatorAngle.setDuration(ANGLE_ANIMATOR_DURATION);
    mObjectAnimatorAngle.setRepeatMode(ValueAnimator.RESTART);
    mObjectAnimatorAngle.setRepeatCount(ValueAnimator.INFINITE);

    mObjectAnimatorSweep = ObjectAnimator.ofFloat(this, mSweepProperty, 360f - MIN_SWEEP_ANGLE * 2);
    mObjectAnimatorSweep.setInterpolator(SWEEP_INTERPOLATOR);
    mObjectAnimatorSweep.setDuration(SWEEP_ANIMATOR_DURATION);
    mObjectAnimatorSweep.setRepeatMode(ValueAnimator.RESTART);
    mObjectAnimatorSweep.setRepeatCount(ValueAnimator.INFINITE);
    mObjectAnimatorSweep.addListener(new SimpleAnimatorListener() {
        @Override
        public void onAnimationRepeat(Animator animation) {
            toggleAppearingMode();
        }
    });
    fractionAnimator = ValueAnimator.ofInt(0, 255);
    fractionAnimator.setInterpolator(ANGLE_INTERPOLATOR);
    fractionAnimator.setDuration(100);
    fractionAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            fraction = animation.getAnimatedFraction();
            mHookPaint.setAlpha((Integer) animation.getAnimatedValue());
            invalidate();
        }
    });
}

四个draw相关方法

private void drawError(Canvas canvas) {
    mError.reset();
    mError.moveTo(fBounds.centerX() + fBounds.width() * 0.2f * fraction, fBounds.centerY() - fBounds.height() * 0.2f * fraction);
    mError.lineTo(fBounds.centerX() - fBounds.width() * 0.2f * fraction, fBounds.centerY() + fBounds.height() * 0.2f * fraction);
    mError.moveTo(fBounds.centerX() - fBounds.width() * 0.2f * fraction, fBounds.centerY() - fBounds.height() * 0.2f * fraction);
    mError.lineTo(fBounds.centerX() + fBounds.width() * 0.2f * fraction, fBounds.centerY() + fBounds.height() * 0.2f * fraction);
    mHookPaint.setColor(mColors[3]);
    canvas.drawPath(mError, mHookPaint);
    canvas.drawArc(fBounds, 0, 360, false, mHookPaint);
}

private void drawHook(Canvas canvas) {
    mHook.reset();
    mHook.moveTo(fBounds.centerX() - fBounds.width() * 0.25f * fraction, fBounds.centerY());
    mHook.lineTo(fBounds.centerX() - fBounds.width() * 0.1f * fraction, fBounds.centerY() + fBounds.height() * 0.18f * fraction);
    mHook.lineTo(fBounds.centerX() + fBounds.width() * 0.25f * fraction, fBounds.centerY() - fBounds.height() * 0.20f * fraction);
    mHookPaint.setColor(mColors[0]);
    canvas.drawPath(mHook, mHookPaint);
    canvas.drawArc(fBounds, 0, 360, false, mHookPaint);

}

private void drawArc(Canvas canvas) {
    float startAngle = mCurrentGlobalAngle - mCurrentGlobalAngleOffset;
    float sweepAngle = mCurrentSweepAngle;
    if (mModeAppearing) {
        mPaint.setColor(gradient(mColors[mCurrentColorIndex], mColors[mNextColorIndex],
                mCurrentSweepAngle / (360 - MIN_SWEEP_ANGLE * 2)));
        sweepAngle += MIN_SWEEP_ANGLE;
    } else {
        startAngle = startAngle + sweepAngle;
        sweepAngle = 360 - sweepAngle - MIN_SWEEP_ANGLE;
    }
    canvas.drawArc(fBounds, startAngle, sweepAngle, false, mPaint);
    if (showArrow) {
        drawTriangle(canvas, startAngle, sweepAngle);
    }
}

public void drawTriangle(Canvas c, float startAngle, float sweepAngle) {
    if (mArrow == null) {
        mArrow = new Path();
        mArrow.setFillType(Path.FillType.EVEN_ODD);
    } else {
        mArrow.reset();
    }

    float x = (float) (mRingCenterRadius * Math.cos(0) + fBounds.centerX());
    float y = (float) (mRingCenterRadius * Math.sin(0) + fBounds.centerY());
    mArrow.moveTo(0, 0);
    mArrow.lineTo(ARROW_WIDTH * mArrowScale, 0);
    mArrow.lineTo((ARROW_WIDTH * mArrowScale / 2), (ARROW_HEIGHT
            * mArrowScale));
    mArrow.offset(x, y);
    mArrow.close();
    c.rotate(startAngle + sweepAngle, fBounds.centerX(),
            fBounds.centerY());
    c.drawPath(mArrow, mPaint);
}

上面的代码就是相关核心的方法了，其实对应的进度条效果就是控制 startAngle和sweepAngle这两个对应的字段，然后不断的调用drawArc()方法。

对于画钩钩或者画叉叉，就是一个ValueAnimator,通过百分比控制缩放和画笔的透明度。

对于drawTriangle()方法，如果你觉得很眼熟的话也很正常，其实这个就是在SwipeRefreshLayout里面抄过来的。。。。。
一开始，我很纠结这个箭头怎么才能跟着进度条一起旋转，自己写的也是有各种问题，另外mArrowScale这个参数在里面其实没有使用的。
如果没有offset偏移量，那么那个path肯定是画在左上角的。

x=mRingCenterRadius +fBounds.centerX();
y=fBounds.centerY();

通过这个一设置，这个path其实就到了右边的中间靠着圆弧的内侧一点去了（因为这里的半径减去了圆弧自己的宽度。。），这么一来，再根据相关的角度旋转角度，就有一种跟着进度条一直转的效果了！

对于drawArc()方法，主要是控制startAngle和sweepAngle这两个变量，mCurrentGlobalAngle的变化范围是（0~360），而mCurrentSweepAngle的变化范围是（0~360f - MIN_SWEEP_ANGLE * 2），为什么要减去两个最小值呢？因为sweepAngle总会加一个或者总会减去一个最小值，所以最小间距还是MIN_SWEEP_ANGLE。
至于什么时候加什么时候减呢？这里有一个变量值mModeAppearing提供记录！那就是当mObjectAnimatorSweep的动画重复的时候，就需要切换一下了。。

mObjectAnimatorSweep.addListener(new SimpleAnimatorListener() {
        @Override
        public void onAnimationRepeat(Animator animation) {
            toggleAppearingMode();
        }
    });
private void toggleAppearingMode() {
    mModeAppearing = !mModeAppearing;
    if (mModeAppearing) {
        mCurrentColorIndex = ++mCurrentColorIndex % 4;
        mNextColorIndex = ++mNextColorIndex % 4;
        mCurrentGlobalAngleOffset = (mCurrentGlobalAngleOffset + MIN_SWEEP_ANGLE * 2) % 360;
    }
}