6amya-rhpma.gif

要完成这样的效果.

1.1 一个字体两种颜色

1.1.1两种字体,需要定义自定义属性

        //获取TypedArray
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.ColorTrackTextView);

        mOriginalColor = typedArray.getColor(R.styleable.ColorTrackTextView_originalColor, mOriginalColor);
        mChangeColor = typedArray.getColor(R.styleable.ColorTrackTextView_changeColor, mChangeColor);
        //回收
        typedArray.recycle();

1.1.2 两种字体,两种画笔

        mOriginalPaint = getPaint(mOriginalColor);
        mChangePaint = getPaint(mChangeColor);

    private Paint getPaint(int color) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(getTextSize());
        //防抖动
        paint.setDither(true);
        return paint;
    }

1.1.3 只绘制一部分区域的字体

用到canvas.clipRect(rect);来裁剪区域

    private void drawText(Canvas canvas, int start, int end, Paint paint) {
        canvas.save();
        //区域
        Rect rect = new Rect(start, 0, end, getHeight());
        //裁剪区域,只允许在这个区域绘制内容
        canvas.clipRect(rect);
        //获取文字
        String text = getText().toString();
        //字体宽度
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        int x = getWidth() / 2 - bounds.width() / 2;
        //基线
        //指定中间位置,求基线
        Paint.FontMetricsInt fontMetricsInt = paint.getFontMetricsInt();
        int baseLine = getHeight() / 2 + (fontMetricsInt.bottom - fontMetricsInt.top) / 2 - fontMetricsInt.bottom;
        canvas.drawText(text, x, baseLine, paint);
        canvas.restore();
    }

1.1.4 提供公共方法

提供进度的公共方法.

    public void setCurrentProgress(double currentProgress) {
        this.mCurrentProgress = currentProgress;
        invalidate();
    }

根据进度计算中间值,根据中间值绘制变色字体

        // 根据进度把中间值算出来
        int middle = (int) (mCurrentProgress * getWidth());

        // 绘制变色
        drawText(canvas, 0, middle, mChangePaint);
        drawText(canvas, middle, getWidth(),mOriginalPaint);

效果

Gif_20180623_212340.gif

结合ViewPager见完整代码.

完整代码:colortracktextview