大概搜了一下關(guān)于文本跳躍的文章，思想大抵都是來自https://github.com/frakbot/JumpingBeans這兒

大概讀了一下源碼，沒看太懂，大致思想應(yīng)該是將需要做跳躍的字符串拆成單個文本，然后對單個文本做動畫。

動畫用到了它自己定義的差值器

 /**
     * A tweaked {@link android.view.animation.AccelerateDecelerateInterpolator}
     * that covers the full range in a fraction of its input range, and holds on
     * the final value on the rest of the input range. By default, this fraction
     * is 65% of the full range.
     *
     * @see JumpingBeans.Builder#DEFAULT_ANIMATION_DUTY_CYCLE
     */
    private static class JumpInterpolator implements TimeInterpolator {

        private final float animRange;

        public JumpInterpolator(float animatedRange) {
            animRange = Math.abs(animatedRange);
        }

        @Override
        public float getInterpolation(float input) {
            // We want to map the [0, PI] sine range onto [0, animRange]
            if (input > animRange) {
                return 0f;
            }
            double radians = (input / animRange) * Math.PI;
            return (float) Math.sin(radians);
        }

    }

然后每個文本啟動動畫的時間延遲不一樣

private void initIfNecessary(float ascent) {
        if (jumpAnimator != null) {
            return;
        }

        this.shift = 0;
        int maxShift = (int) ascent / 2;
        jumpAnimator = ValueAnimator.ofInt(0, maxShift);
        jumpAnimator
                .setDuration(loopDuration)
                .setStartDelay(delay);
        jumpAnimator.setInterpolator(new JumpInterpolator(animatedRange));
        jumpAnimator.setRepeatCount(ValueAnimator.INFINITE);
        jumpAnimator.setRepeatMode(ValueAnimator.RESTART);
        jumpAnimator.addUpdateListener(this);
        jumpAnimator.start();
    }

這個setStartDelay(delay)中的delay是由單個文本在字符串中的位置影響的。

在JumpingBeansSpan這個類中，最關(guān)鍵的代碼應(yīng)該是

@Override
    public void updateMeasureState(TextPaint tp) {
        initIfNecessary(tp.ascent());
        tp.baselineShift = shift;
    }

    @Override
    public void updateDrawState(TextPaint tp) {
        initIfNecessary(tp.ascent());
        tp.baselineShift = shift;
    }

動畫正是從這兒啟動的，但是沒有找到這兩個方法調(diào)用時機，只是debug的時候可以debug到。

拆分文本的方法是在JumpingBeans這個類中

   private JumpingBeansSpan[] buildWavingSpans(SpannableStringBuilder sbb) {
            JumpingBeansSpan[] spans;
            if (waveCharDelay == DEFAULT_WAVE_CHAR_DELAY) {
                waveCharDelay = loopDuration / (3 * (endPos - startPos));
            }

            spans = new JumpingBeansSpan[endPos - startPos];
            for (int pos = startPos; pos < endPos; pos++) {
                JumpingBeansSpan jumpingBean =
                        new JumpingBeansSpan(textView, loopDuration, pos - startPos, waveCharDelay, animRange);
                sbb.setSpan(jumpingBean, pos, pos + 1, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
                spans[pos - startPos] = jumpingBean;
            }
            return spans;
        }