七：按钮控制ViewPager的左右翻页
最后更新于：2022-04-01 06:42:21
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](http://blog.sina.com.cn/s/blog_4b20ae2e0101fkpz.html)
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
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。