【Android】解决Fragment多层嵌套时onActivityResult无法正确回调的问题

来源:转载

前言:

Fragment也可以使用startActivityForResult方法去打开一个Activity,然后在其onActivityResult方法中处理结果,可是当Fragment嵌套的时候,由于FragmentActivity的BUG导致只会回调最外那层Fragment的onActivityResult方法,于是乎当前Fragment就收不到结果了。


BUG分析:

解决这个问题之前我们先通过源码分析一下是什么原因导致的,以22.2.1版本的support-v4库为例


我们先从Fragment的startActivityForResult开始分析


public void startActivityForResult(Intent intent, int requestCode) {
if(this.mActivity == null) {
throw new IllegalStateException("Fragment " + this + " not attached to Activity");
} else {
this.mActivity.startActivityFromFragment(this, intent, requestCode);
}
}

很明显直接调用了FragmentActivity的startActivityFromFragment方法


public void startActivityFromFragment(Fragment fragment, Intent intent, int requestCode) {
if(requestCode == -1) {
super.startActivityForResult(intent, -1);
} else if((requestCode & -65536) != 0) {
throw new IllegalArgumentException("Can only use lower 16 bits for requestCode");
} else {
super.startActivityForResult(intent, (fragment.mIndex + 1 << 16) + (requestCode & '/uffff'));
}
}

在这里将requestCode和Fragment的mIndex融合成了一个整型作为新的requestCode,那么新的requestCode的高16位表示Fragment的索引,低16为表示原本的requestCode,看来这里是用Fragment的mIndex作为查找依据的


接下来再看FragmentActivity的onActivityResult方法


protected void onActivityResult(int requestCode, int resultCode, Intent data) {
this.mFragments.noteStateNotSaved();
int index = requestCode >> 16;
if(index != 0) {
--index;
if(this.mFragments.mActive != null && index >= 0 && index < this.mFragments.mActive.size()) {
Fragment frag = (Fragment)this.mFragments.mActive.get(index);
if(frag == null) {
Log.w("FragmentActivity", "Activity result no fragment exists for index: 0x" + Integer.toHexString(requestCode));
} else {
frag.onActivityResult(requestCode & '/uffff', resultCode, data);
}
} else {
Log.w("FragmentActivity", "Activity result fragment index out of range: 0x" + Integer.toHexString(requestCode));
}
} else {
super.onActivityResult(requestCode, resultCode, data);
}
}

在这里取出requestCode的高16位,不等0就是子Fragment的mIndex,但是接下来却直接从Activity的Fragment列表中根据索引去找Fragment,如果你的Fragment是被子Fragment的childFragmentManager管理的话这样是绝对找不到的,于是乎答案很明了了。


解决问题:

解决这个问题的办法有两个
第一个是直接升级support-v4到23.2.0以上的版本,因为23.2.0以上就修复了这个BUG,具体怎么解决的就不再赘述了有兴趣的可自行研究,但由于种种原因没办法升级23.2.0的还大有人在
第二种办法就是自己动手丰衣足食,在Fragment层重写相关方法解决问题


接下来着重介绍自己动手丰衣足食的办法,完整实现如下:


public class ForResultNestedCompatFragment extends Fragment {
private ForResultNestedCompatFragment forResultChildFragment;
@Override
public void startActivityForResult(Intent intent, int requestCode) {
Fragment parentFragment = getParentFragment();
if (parentFragment != null && parentFragment instanceof ForResultNestedCompatFragment) {
((ForResultNestedCompatFragment) parentFragment).startActivityForResultFromChildFragment(intent, requestCode, this);
} else {
forResultChildFragment = null;
super.startActivityForResult(intent, requestCode);
}
}
private void startActivityForResultFromChildFragment(Intent intent, int requestCode, ForResultNestedCompatFragment childFragment) {
forResultChildFragment = childFragment;
Fragment parentFragment = getParentFragment();
if (parentFragment != null && parentFragment instanceof ForResultNestedCompatFragment) {
((ForResultNestedCompatFragment) parentFragment).startActivityForResultFromChildFragment(intent, requestCode, this);
} else {
super.startActivityForResult(intent, requestCode);
}
}
@Override
public final void onActivityResult(int requestCode, int resultCode, Intent data) {
if (forResultChildFragment != null) {
forResultChildFragment.onActivityResult(requestCode, resultCode, data);
forResultChildFragment = null;
} else {
onActivityResultNestedCompat(requestCode, resultCode, data);
}
}
public void onActivityResultNestedCompat(int requestCode, int resultCode, Intent data) {
}
}

具体思路一句话概括就是startActivityForResult的时候一层一层往上让父Fragment持有子Fragment的引用,回调onActivityResult的时候父Fragment再一层一层传给子Fragment


具体用法就是让所有的Fragment都继承ForResultNestedCompatFragment,然后用onActivityResultNestedCompat方法替换onActivityResult方法


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