Fragment.onCreateAnimator()的文档在哪里？

Question

该Fragment.onCreateAnimator(int, boolean, int)方法的整个文档包含以下文本:

"片段加载动画时调用."

而已.没有关于参数的解释.

参数是什么意思？即使是源代码也没有透露太多.

Answer 1

这个onCreateAnimator方法很奇怪.我见过的原型是这样的:

public Animator onCreateAnimator(int transit, boolean enter, int nextAnim)

int transit - 过渡型,正如sandrstar所说

boolean enter - 如果'进入'则为true,否则为false

int nextAnim- 即将播放的动画的资源ID.

因此,例如,如果您尝试执行卡片翻转,请从文档中:

// Create and commit a new fragment transaction that adds the fragment for the back of
// the card, uses custom animations, and is part of the fragment manager's back stack.
BackOfCardFragment backFragment = new BackOfCardFragment();

getFragmentManager()
    .beginTransaction()

    // Replace the default fragment animations with animator resources representing
    // rotations when switching to the back of the card, as well as animator
    // resources representing rotations when flipping back to the front (e.g. when
    // the system Back button is pressed).
    .setCustomAnimations(
         R.animator.card_flip_right_in, R.animator.card_flip_right_out,
         R.animator.card_flip_left_in, R.animator.card_flip_left_out)

    // Replace any fragments currently in the container view with a fragment
    // representing the next page (indicated by the just-incremented currentPage
    // variable).
    .replace(R.id.container_view, backFragment)

    // Add this transaction to the back stack, allowing users to press Back
    // to get to the front of the card.
    .addToBackStack(null)

    // Commit the transaction.
    .commit();

注意:上例中的R.id.container_view是包含您要替换的现有片段的ViewGroup的ID.

当执行上面的代码时,onCreateAnimator将调用该方法,并且该nextAnim参数将是传递给setCustomAnimations()函数的四个动画ID之一,即R.animator.card_flip_right_in,R.animator.card_flip_right_out ......等.

这一开始似乎没有用,因为它没有为您提供可以附加监听器的实际Animator对象的引用.但奇怪的是,你可以直接从nextAnim资源中充气另一个Animator ,然后将听众附加到那个,奇怪的是,它会在正确的时间触发所有被覆盖的回调:

@Override
public Animator onCreateAnimator(int transit, boolean enter, int nextAnim) {
    Animator animator = null;
    // In this example, i want to add a listener when the card_flip_right_in animation
    // is about to happen.
    if (nextAnim == R.animator.card_flip_right_in) {
        animator = AnimatorInflater.loadAnimator(getActivity(), nextAnim);
        // * Sometimes onCreateAnimator will be called and nextAnim will be 0, 
        //   causing animator to be null.
        // * I wanted to add a listener when the fragment was entering - 
        //   your use case may be different.
        if (animator != null && enter) {

            animator.addListener(new Animator.AnimatorListener() {
                @Override
                public void onAnimationStart(Animator animation) {
                   // Do something when the card flip animation begins
                }

                @Override
                public void onAnimationEnd(Animator animation) {
                   // Do something as soon as the card flip animation is over
                }

                @Override
                public void onAnimationCancel(Animator animation) {
                }

                @Override
                public void onAnimationRepeat(Animator animation) {
                }
            });
        }
    }
    return animator;
}

通过这种方式,您应该能够将侦听器添加到片段转换动画器中,就像您自己创建它们一样.

Answer 2

基于FragmentManager代码和FragmentManagerImpl.loadAnimator(android.app.Fragment,int,boolean,int)的用法,似乎Fragment.onCreateAnimator(int,boolean,int)允许您为片段隐藏,显示,更改状态定义自己的动画.但是,我从未在真正的应用程序中看到它的用法.

关于参数:

• int transit- 过渡类型(常量FragmentTransaction,例如在这里使用);
• boolean enter- true如果状态输入,则为false - 否则;
• int transitionStyle- 来自资源的样式的id(该样式可能包含错过的动画onCreateAnimator);