为了实现左右翻页的效果，使用了ViewPager，它会很方便的实现左右滑动后翻页。

这时需要自己也加上两个button来实现同样的操作，如何实现呢？网上一篇blog帮了忙啦。

【Android】按钮控制ViewPager的左右翻页，保留原有的动画效果

ViewPager的一个公共方法arrowScroll，查看代码我们可以有两个重要的发现：

    public boolean executeKeyEvent(KeyEvent event) {
        boolean handled = false;
        if (event.getAction() == KeyEvent.ACTION_DOWN) {
            switch (event.getKeyCode()) {
                case KeyEvent.KEYCODE_DPAD_LEFT://键盘方向键左键的控制，向左翻页
                    handled = arrowScroll(FOCUS_LEFT);//FOCUS_LEFT:17
                    break;
                case KeyEvent.KEYCODE_DPAD_RIGHT://右键
                    handled = arrowScroll(FOCUS_RIGHT);//FOCUS_RIGHT:66
                    break;
                case KeyEvent.KEYCODE_TAB:
                    if (Build.VERSION.SDK_INT >= 11) {
                        // The focus finder had a bug handling FOCUS_FORWARD and FOCUS_BACKWARD
                        // before Android 3.0. Ignore the tab key on those devices.
                        if (KeyEventCompat.hasNoModifiers(event)) {
                            handled = arrowScroll(FOCUS_FORWARD);//FOCUS_FORWARD:2
                        } else if (KeyEventCompat.hasModifiers(event, KeyEvent.META_SHIFT_ON)) {
                            handled = arrowScroll(FOCUS_BACKWARD);//FOCUS_BACKWARD:1
                        }
                    }
                    break;
            }
        }
        return handled;
    }

    public boolean arrowScroll(int direction) {
        View currentFocused = findFocus();
        if (currentFocused == this) currentFocused = null;

        boolean handled = false;

        View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused,
                direction);
        if (nextFocused != null && nextFocused != currentFocused) {
            if (direction == View.FOCUS_LEFT) {
                // If there is nothing to the left, or this is causing us to
                // jump to the right, then what we really want to do is page left.
                final int nextLeft = getChildRectInPagerCoordinates(mTempRect, nextFocused).left;
                final int currLeft = getChildRectInPagerCoordinates(mTempRect, currentFocused).left;
                if (currentFocused != null && nextLeft >= currLeft) {
                    handled = pageLeft();
                } else {
                    handled = nextFocused.requestFocus();
                }
            } else if (direction == View.FOCUS_RIGHT) {
                // If there is nothing to the right, or this is causing us to
                // jump to the left, then what we really want to do is page right.
                final int nextLeft = getChildRectInPagerCoordinates(mTempRect, nextFocused).left;
                final int currLeft = getChildRectInPagerCoordinates(mTempRect, currentFocused).left;
                if (currentFocused != null && nextLeft <= currLeft) {
                    handled = pageRight();
                } else {
                    handled = nextFocused.requestFocus();
                }
            }
        } else if (direction == FOCUS_LEFT || direction == FOCUS_BACKWARD) {//17 or 1
            // Trying to move left and nothing there; try to page.
            handled = pageLeft();
        } else if (direction == FOCUS_RIGHT || direction == FOCUS_FORWARD) {//66 or 2
            // Trying to move right and nothing there; try to page.
            handled = pageRight();
        }
        if (handled) {
            playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));
        }
        return handled;
    }

也就是说，我们调用arrowScroll方法用参数1或者17就可以实现向左翻页；参数2或66就可以实现向右翻页。

后记：

当你的UI中有EditText这种获得focus的widget时，则必须用17和66，否则要报错。