前言

最近要用到一个带下载进度的按钮，各种搜索了一波，很抱歉（/TДT)/ ，实在没有发现自己想要的效果，没办法只能自己尝试实现了一个了。

效果展示

demo

支持圆角，支持是否显示边框
中间文字会根据下载进度有个变色的效果
下载完成后，“安装中“有一个 loading 的动画效果

难点分析

1 . 怎样实现中间文字会根据下载进度有个变色的效果？

可以通过 LinearGradient 实现字体渐变的效果，参考了LinearGradient与闪动文字效果，具体在代码中解释。

2 . 按钮的背景根据进度不断铺满？

以下图为例，根据当前进度画出一个和整个按钮相同大小的蓝色矩形（ dst ），再画一个同样大小的白色矩形，只显示白色矩形中两个重叠的部分不就好了吗？对，我们联想到了两个图层重叠时的显示模式，就是这里的 SRC_ATOP 模式。

3 . “安装中“有一个 loading 的动画效果？

网上已经有很多成熟的 loading 动画效果，理解一下它们的源码，自己实现一下就可以了，我这里参考了AVLoadingIndicatorView 中的两个不错的动画效果，当然你也可以修改成你自己喜欢的效果。

实现

来到了贴代码时间，O(∩_∩)O，其实就是按照自定义控件的基本流程

1 . 定义自定义属性

Property	Format	Default
progress_btn_radius	dimension	0dp
progress_btn_background_color	color	3385FF
progress_btn_background_second_color	color	E8E8E8
progress_btn_text_color	color	progress_btn_background_color
progress_btn_text_cover_color	color	Color.WHITE
progress_btn_border_width	dimension	2dp
progress_btn_ball_style	enum	STYLE_BALL_JUMP

STYLE_BALL_PULSE

STYLE_BALL_PULSE

STYLE_BALL_JUMP

STYLE_BALL_JUMP

这张图可能更加直观吧:

2 . 绘制按钮背景（根据不同状态绘制不同的效果）

    private void drawBackground(Canvas canvas) {

        mBackgroundBounds = new RectF();
        //根据Border宽度得到Button的显示区域
        mBackgroundBounds.left = showBorder ? mBorderWidth : 0;
        mBackgroundBounds.top = showBorder ? mBorderWidth : 0;
        mBackgroundBounds.right = getMeasuredWidth() - (showBorder ? mBorderWidth : 0);
        mBackgroundBounds.bottom = getMeasuredHeight() - (showBorder ? mBorderWidth : 0);

        if (showBorder) {
            mBackgroundPaint.setStyle(Paint.Style.STROKE);
            mBackgroundPaint.setColor(mBackgroundColor);
            mBackgroundPaint.setStrokeWidth(mBorderWidth);
            canvas.drawRoundRect(mBackgroundBounds, mButtonRadius, mButtonRadius, mBackgroundPaint);
        }
        mBackgroundPaint.setStyle(Paint.Style.FILL);
        //color
        switch (mState) {
            case STATE_NORMAL:
                mBackgroundPaint.setColor(mBackgroundColor);
                canvas.drawRoundRect(mBackgroundBounds, mButtonRadius, mButtonRadius, mBackgroundPaint);
                break;
            case STATE_PAUSE:
            case STATE_DOWNLOADING:
                //计算当前的进度
                mProgressPercent = mProgress / (mMaxProgress + 0f);
                mBackgroundPaint.setColor(mBackgroundSecondColor);
                canvas.save();
                //画出dst图层
                canvas.drawRoundRect(mBackgroundBounds, mButtonRadius, mButtonRadius, mBackgroundPaint);
                //设置图层显示模式为 SRC_ATOP
                PorterDuffXfermode porterDuffXfermode = new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP);
                mBackgroundPaint.setColor(mBackgroundColor);
                mBackgroundPaint.setXfermode(porterDuffXfermode);
                //计算 src 矩形的右边界
                float right = mBackgroundBounds.right * mProgressPercent;
                //在dst画出src矩形
                canvas.drawRect(mBackgroundBounds.left, mBackgroundBounds.top, right, mBackgroundBounds.bottom, mBackgroundPaint);
                canvas.restore();
                mBackgroundPaint.setXfermode(null);
                break;
            case STATE_FINISH:
                mBackgroundPaint.setColor(mBackgroundColor);
                canvas.drawRoundRect(mBackgroundBounds, mButtonRadius, mButtonRadius, mBackgroundPaint);
                break;
        }
    }

3 . 绘制文字

  private void drawTextAbove(Canvas canvas) {
        //计算Baseline绘制的Y坐标
        final float y = canvas.getHeight() / 2 - (mTextPaint.descent() / 2 + mTextPaint.ascent() / 2);
        if (mCurrentText == null) {
            mCurrentText = "";
        }
        final float textWidth = mTextPaint.measureText(mCurrentText.toString());
        mTextBottomBorder = y;
        mTextRightBorder = (getMeasuredWidth() + textWidth) / 2;
        //color
        switch (mState) {
            case STATE_NORMAL:
                mTextPaint.setShader(null);
                mTextPaint.setColor(mTextCoverColor);
                canvas.drawText(mCurrentText.toString(), (getMeasuredWidth() - textWidth) / 2, y, mTextPaint);
                break;
            case STATE_PAUSE:
            case STATE_DOWNLOADING:

                //进度条压过距离
                float coverLength = getMeasuredWidth() * mProgressPercent;
                //开始渐变指示器
                float indicator1 = getMeasuredWidth() / 2 - textWidth / 2;
                //结束渐变指示器
                float indicator2 = getMeasuredWidth() / 2 + textWidth / 2;
                //文字变色部分的距离
                float coverTextLength = textWidth / 2 - getMeasuredWidth() / 2 + coverLength;
                float textProgress = coverTextLength / textWidth;
                if (coverLength <= indicator1) {
                    mTextPaint.setShader(null);
                    mTextPaint.setColor(mTextColor);
                } else if (indicator1 < coverLength && coverLength <= indicator2) {
                    //设置变色效果
                    mProgressTextGradient = new LinearGradient((getMeasuredWidth() - textWidth) / 2, 0, (getMeasuredWidth() + textWidth) / 2, 0,
                            new int[]{mTextCoverColor, mTextColor},
                            new float[]{textProgress, textProgress + 0.001f},
                            Shader.TileMode.CLAMP);
                    mTextPaint.setColor(mTextColor);
                    mTextPaint.setShader(mProgressTextGradient);
                } else {
                    mTextPaint.setShader(null);
                    mTextPaint.setColor(mTextCoverColor);
                }
                canvas.drawText(mCurrentText.toString(), (getMeasuredWidth() - textWidth) / 2, y, mTextPaint);
                break;
            case STATE_FINISH:
                mTextPaint.setColor(mTextCoverColor);
                canvas.drawText(mCurrentText.toString(), (getMeasuredWidth() - textWidth) / 2, y, mTextPaint);
                drawLoadingBall(canvas);
                break;

        }

    }

4 . 两种动画效果

STYLE_BALL_PULSE

 public ArrayList<ValueAnimator> createBallPulseAnimators() {
        ArrayList<ValueAnimator> animators = new ArrayList<>();
        int[] delays = new int[]{120, 240, 360};
        for (int i = 0; i < 3; i++) {
            final int index = i;

            ValueAnimator scaleAnim = ValueAnimator.ofFloat(1, 0.3f, 1);

            scaleAnim.setDuration(750);
            scaleAnim.setRepeatCount(-1);
            scaleAnim.setStartDelay(delays[i]);

            scaleAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    scaleFloats[index] = (float) animation.getAnimatedValue();
                    postInvalidate();
                }
            });
            animators.add(scaleAnim);
        }
        return animators;
    }

STYLE_BALL_JUMP

 public ArrayList<ValueAnimator> createBallJumpAnimators() {
        ArrayList<ValueAnimator> animators = new ArrayList<>();
        int[] delays = new int[]{70, 140, 210};
        for (int i = 0; i < 3; i++) {
            final int index = i;
            ValueAnimator scaleAnim = ValueAnimator.ofFloat(mTextBottomBorder, mTextBottomBorder - mBallRadius * 2, mTextBottomBorder);
            scaleAnim.setDuration(600);
            scaleAnim.setRepeatCount(-1);
            scaleAnim.setStartDelay(delays[i]);
            scaleAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    translateYFloats[index] = (float) animation.getAnimatedValue();
                    postInvalidate();
                }
            });
            animators.add(scaleAnim);
        }
        return animators;
    }

总结

有什么不明白的可以下载完整源码学习一下，ps：自己也是站在巨人的肩膀上，才能够完整实现这个自定义控件，很感谢那些乐于分享和开源的大神，也希望可以帮助有需要的同学！
如果您觉得对你有所帮助，轻轻点一下star，来鼓励一下我，谢谢！o(∩_∩)o

源码下载

参考

LinearGradient与闪动文字效果

Paint之setXfermode(一)

安卓自定义View教程目录

Android 自定义view之FontMetric