fragment中的add和replace方法的区别浅析

public abstract FragmentTransaction add (int containerViewId, Fragment fragment, String tag)
Add a fragment to the activity state. This fragment may optionally also have its view (if Fragment.onCreateView returns non-null) into a Container view of the activity.

public abstract FragmentTransaction replace (int containerViewId, Fragment fragment, String tag)
Replace an existing fragment that was added to a container. This is essentially the same as calling remove(Fragment) for all currently added fragments that were added with the same containerViewId and then add(int, Fragment, String) with the same arguments given here.

public FragmentTransaction add(int containerViewId, Fragment fragment, String tag) {
 doAddOp(containerViewId, fragment, tag, OP_ADD);
 return this;
}

public FragmentTransaction replace(int containerViewId, Fragment fragment, String tag) {
 if (containerViewId == 0) {
 throw new IllegalArgumentException("Must use non-zero containerViewId");
 }
 doAddOp(containerViewId, fragment, tag, OP_REPLACE);
 return this;
}

private void doAddOp(int containerViewId, Fragment fragment, String tag, int opcmd) {
 fragment.mFragmentManager = mManager;
 if (tag != null) {
 if (fragment.mTag != null && !tag.equals(fragment.mTag)) {
 throw new IllegalStateException("Can't change tag of fragment "
  + fragment + ": was " + fragment.mTag
  + " now " + tag);
 }
 fragment.mTag = tag;
 }
 if (containerViewId != 0) {
 if (fragment.mFragmentId != 0 && fragment.mFragmentId != containerViewId) {
 throw new IllegalStateException("Can't change container ID of fragment "
  + fragment + ": was " + fragment.mFragmentId
  + " now " + containerViewId);
 }
 fragment.mContainerId = fragment.mFragmentId = containerViewId;
 }
 Op op = new Op();
 op.cmd = opcmd;
 op.fragment = fragment;
 addOp(op);
}

public void run() {
 if (FragmentManagerImpl.DEBUG) {
 Log.v(TAG, "Run: " + this);
 }
 if (mAddToBackStack) {
 if (mIndex < 0) {
 throw new IllegalStateException("addToBackStack() called after commit()");
 }
 }
 bumpBackStackNesting(1);
 SparseArray<Fragment> firstOutFragments = new SparseArray<Fragment>();
 SparseArray<Fragment> lastInFragments = new SparseArray<Fragment>();
 calculateFragments(firstOutFragments, lastInFragments);
 beginTransition(firstOutFragments, lastInFragments, false);
 // 获取队列的头
 Op op = mHead;
 while (op != null) {
 switch (op.cmd) {
 case OP_ADD: {
 Fragment f = op.fragment;
 f.mNextAnim = op.enterAnim;
 mManager.addFragment(f, false);//添加
 }
 break;
 case OP_REPLACE: {
 Fragment f = op.fragment;
 if (mManager.mAdded != null) {
  for (int i = 0; i < mManager.mAdded.size(); i++) {
  Fragment old = mManager.mAdded.get(i);
  if (FragmentManagerImpl.DEBUG) {
  Log.v(TAG,
   "OP_REPLACE: adding=" + f + " old=" + old);
  }
  if (f == null || old.mContainerId == f.mContainerId) {
  if (old == f) {
  op.fragment = f = null;
  } else {
  if (op.removed == null) {
   op.removed = new ArrayList<Fragment>();
  }
  op.removed.add(old);
  old.mNextAnim = op.exitAnim;
  if (mAddToBackStack) {
   old.mBackStackNesting += 1;
   if (FragmentManagerImpl.DEBUG) {
   Log.v(TAG, "Bump nesting of "
   + old + " to " + old.mBackStackNesting);
   }
  }
  mManager.removeFragment(old, mTransition, mTransitionStyle);//删除
  }
  }
  }
 }
 if (f != null) {
  f.mNextAnim = op.enterAnim;
  mManager.addFragment(f, false);//添加
 }
 }
 break;
 case OP_REMOVE: {
 Fragment f = op.fragment;
 f.mNextAnim = op.exitAnim;
 mManager.removeFragment(f, mTransition, mTransitionStyle);
 }
 break;
 case OP_HIDE: {
 Fragment f = op.fragment;
 f.mNextAnim = op.exitAnim;
 mManager.hideFragment(f, mTransition, mTransitionStyle);
 }
 break;
 case OP_SHOW: {
 Fragment f = op.fragment;
 f.mNextAnim = op.enterAnim;
 mManager.showFragment(f, mTransition, mTransitionStyle);
 }
 break;
 case OP_DETACH: {
 Fragment f = op.fragment;
 f.mNextAnim = op.exitAnim;
 mManager.detachFragment(f, mTransition, mTransitionStyle);
 }
 break;
 case OP_ATTACH: {
 Fragment f = op.fragment;
 f.mNextAnim = op.enterAnim;
 mManager.attachFragment(f, mTransition, mTransitionStyle);
 }
 break;
 default: {
 throw new IllegalArgumentException("Unknown cmd: " + op.cmd);
 }
 }
 op = op.next;//队列的下一个
 }
 mManager.moveToState(mManager.mCurState, mTransition,
 mTransitionStyle, true);
 if (mAddToBackStack) {
 mManager.addBackStackState(this);
 }
}

public void addFragment(Fragment fragment, boolean moveToStateNow) {
 if (mAdded == null) {
 mAdded = new ArrayList<Fragment>();
 }
 if (DEBUG) Log.v(TAG, "add: " + fragment);
 makeActive(fragment);
 if (!fragment.mDetached) {
 if (mAdded.contains(fragment)) {
 throw new IllegalStateException("Fragment already added: " + fragment);
 }
 mAdded.add(fragment);
 fragment.mAdded = true;
 fragment.mRemoving = false;
 if (fragment.mHasMenu && fragment.mMenuVisible) {
 mNeedMenuInvalidate = true;
 }
 if (moveToStateNow) {
 moveToState(fragment);
 }
 }
}

public boolean dispatchCreateOptionsMenu(Menu menu, MenuInflater inflater) {
 boolean show = false;
 ArrayList<Fragment> newMenus = null;
 if (mAdded != null) {
 for (int i=0; i<mAdded.size(); i++) {
 Fragment f = mAdded.get(i);
 if (f != null) {
 if (f.performCreateOptionsMenu(menu, inflater)) {
  show = true;
  if (newMenus == null) {
  newMenus = new ArrayList<Fragment>();
  }
  newMenus.add(f);
 }
 }
 }
 }
 if (mCreatedMenus != null) {
 for (int i=0; i<mCreatedMenus.size(); i++) {
 Fragment f = mCreatedMenus.get(i);
 if (newMenus == null || !newMenus.contains(f)) {
 f.onDestroyOptionsMenu();
 }
 }
 }
 mCreatedMenus = newMenus;
 return show;
}