Android 動畫分三種,其中屬性動畫爲我們最常用動畫,且能滿足項目中開發幾乎全部需求,google官方包支持3.0+,我們可以引用三方包nineoldandroids來失陪到低版本。本例子中就是用屬性動畫實現效果。
對普通的View做動畫,我們只要定義好要的動畫ObjectAnimator或AnimatorSet,然後設置屬性啓動及可。但是,對ListView做動畫應該如何、什麼時候、在什麼地方、對哪個View做動畫屬性呢?
github上有成熟的listview動畫包 https://github.com/nhaarman/ListViewAnimations.git , 基本可以滿足比較炫的效果,比如google+動態list加載,各種動態list顯示及刪除。問題是,如果不能滿足我們的需求,如何實現自己想要的ListView動畫效果呢?研究github上項目實現原理髮現並不複雜,下面我們就參考開源項目實現自己的ListView動畫效果。
要想對ListView的Item做動畫,首先想到的是Adapter的getView()方法。在getView方面裏可以獲得每個Item view,然後定義好動畫效果,結合動畫需求對contentView做動畫。
如需要做一個刪除item時的動畫,可以在getView時把View和position傳給做的動畫或動畫集,這個比較簡單見代碼:
public static AnimatorSet buildListRemoveAnimator(final View view, final List list,
final MyAnimListAdapter adapter, final int index) {
AnimatorListener al = new AnimatorListener() {
@Override
public void onAnimationStart(Animator animation) {
// TODO Auto-generated method stub
}
@Override
public void onAnimationRepeat(Animator animation) {
// TODO Auto-generated method stub
}
@Override
public void onAnimationEnd(Animator animation) {
// TODO Auto-generated method stub
list.remove(index);
ViewHolder vh = (ViewHolder) view.getTag();
vh.needInflate = true;
adapter.notifyDataSetChanged();
}
@Override
public void onAnimationCancel(Animator animation) {
// TODO Auto-generated method stub
}
};
AnimatorSet animatorSet = new AnimatorSet();
Animator anim = ObjectAnimator.ofFloat(view, "rotationX", 0, 90);
Animator animb = ObjectAnimator.ofFloat(view, "alpha", 1, 0);
ValueAnimator valueAnimator = ValueAnimator.ofFloat(0, 1);
final int height = view.getMeasuredHeight();
valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
// TODO Auto-generated method stub
if (animation.getAnimatedFraction() >= 1) {
view.setVisibility(View.GONE);
}
else {
view.getLayoutParams().height = height
- (int) (height * animation.getAnimatedFraction());
view.requestLayout();
}
}
});
anim.setDuration(ANIMATION_DURATION);
animb.setDuration(ANIMATION_DURATION);
valueAnimator.setDuration(ANIMATION_DURATION + ANIMATION_DURATION + 100);
animatorSet.playTogether(anim, animb, valueAnimator);
animatorSet.addListener(al);
return animatorSet;
}
如何做一個listview動態現實每個Item的顯示效果。這個教刪除複雜,需要計算每個item動畫的開始時間,及判斷是否動畫現實,還有就是顯示動畫要按照什麼樣的規則或是順序, 計算動畫現實的時間等因素。並且不好優化list的性能,及顯示效果。下面的例子只是實現了基本動畫效果,性能優化欠缺。
public static AnimatorSet buildShowAnimatorList(ViewGroup parent, ListView list, View view, long mAnimationStartMillis,
int mLastAnimatedPosition, int mFirstAnimatedPosition) {
if (mAnimationStartMillis == -1) {
mAnimationStartMillis = System.currentTimeMillis();
}
ViewHelper.setAlpha(view, 0);
Animator alphaAnimator = ObjectAnimator.ofFloat(view, "alpha", 0, 1);
Animator rx = ObjectAnimator.ofFloat(view, "rotationX", -90, 0);
AnimatorSet set = new AnimatorSet();
set.playTogether(alphaAnimator, rx);
set.setStartDelay(calculateAnimationDelay(list, mLastAnimatedPosition, mFirstAnimatedPosition,mAnimationStartMillis));
set.setDuration(DEFAULTANIMATIONDELAYMILLIS);
set.start();
return set;
}
private static long calculateAnimationDelay(ListView list, int last, int first,long starmill) {
long delay;
int lastVisiblePosition = list.getLastVisiblePosition();
int firstVisiblePosition = list.getFirstVisiblePosition();
int numberOfItemsOnScreen = lastVisiblePosition - firstVisiblePosition;
int numberOfAnimatedItems = last - first;
if (numberOfItemsOnScreen + 1 < numberOfAnimatedItems) {
delay = DEFAULTANIMATIONDELAYMILLIS;
} else {
long delaySinceStart = (last - first + 1)
* DEFAULTANIMATIONDELAYMILLIS;
delay = starmill + DEFAULTANIMATIONDELAYMILLIS + delaySinceStart
- System.currentTimeMillis();
}
return Math.max(0, delay);
}
參照上面的方法可以實現自己想要的ListView Item動畫,並且可以去自定義想要的效果。
本例源碼地址:
https://github.com/CankingApp/ListAnimator
多多提建議,多多交流~