Fragment add、remove、delete、show、hide源代码阅读

 Fragment add 、remove 、replace、show、hide原理

FragmentManager  FragmentTransaction FragmentManagerImpl

BackStackRecord

（1）Activity的getFragmentManager()方法

public FragmentManager getFragmentManager() {
 return mFragments;
}

其中mFragments为

final FragmentManagerImpl mFragments = new FragmentManagerImpl();

（2）FragmentManagerImpl extends FragmentManager，看下它的beginTransaction()方法

@Override
public FragmentTransaction beginTransaction() {
 return new BackStackRecord(this);
}

其中BackStackRecord extends FragmentTransaction implements Runnable

（3）看下BackStackRecord的add方法

public FragmentTransaction add(Fragment fragment, String tag) {
    doAddOp(0, fragment, tag, OP_ADD);
 return this;
}

其中doAddOp中主要是调用封装Op并调用addOp方法

Op op = new Op();
op.cmd = opcmd;
op.fragment = fragment;
addOp(op);

（4）看下BackStackRecord的addOp方法

void addOp(Op op) {
 if (mHead == null) {
 mHead = mTail = op;
    } else {
        op.prev = mTail;
 mTail.next = op;
 mTail = op;
    }
    op.enterAnim = mEnterAnim;
    op.exitAnim = mExitAnim;
    op.popEnterAnim = mPopEnterAnim;
    op.popExitAnim = mPopExitAnim;
 mNumOp++;
}

是加入到一个循环链表中

（5）看下BackStackRecord的commit方法

public int commit() {
return commitInternal(false);
}

和commitInternal方法

int commitInternal(boolean allowStateLoss) {
 if (mCommitted) {
 throw new IllegalStateException("commit already called");
    }
 if (FragmentManagerImpl.DEBUG) {
        Log.v(TAG, "Commit: " + this);
        LogWriter logw = new LogWriter(Log.VERBOSE, TAG);
        PrintWriter pw = new FastPrintWriter(logw, false, 1024);
        dump(" ", null, pw, null);
        pw.flush();
    }
 mCommitted = true;
 if (mAddToBackStack) {
 mIndex = mManager.allocBackStackIndex(this);
    } else {
 mIndex = -1;
    }
 mManager.enqueueAction(this, allowStateLoss);
 return mIndex;
}

执行FragmentManagerImpl的enqueueAction

public void enqueueAction(Runnable action, boolean allowStateLoss) {
 if (!allowStateLoss) {
        checkStateLoss();
    }
 synchronized (this) {
 if (mDestroyed || mActivity == null) {
 throw new IllegalStateException("Activity has been destroyed");
        }
 if (mPendingActions == null) {
 mPendingActions = new ArrayList<Runnable>();
        }
 mPendingActions.add(action);
 if (mPendingActions.size() == 1) {
 mActivity.mHandler.removeCallbacks(mExecCommit);
 mActivity.mHandler.post(mExecCommit);
        }
    }
}

直接插入到UI线程中执行或者在FragmentManagerImpl的execPendingActions()中执行。

（6）还记得BackStackRecord implements Runnable，它执行是在run()方法中

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);

    Op op = mHead;
 while (op != null) {
 switch (op.cmd) {
 case OP_ADD: {
                Fragment f = op.fragment;
                f.mNextAnim = op.enterAnim;
 mManager.addFragment(f, false);
            }
 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);
                            }
                        }
                    }
                }
 if (f != null) {
                    f.mNextAnim = op.enterAnim;
 mManager.addFragment(f, false);
                }
            }
 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;
    }

 mManager.moveToState(mManager.mCurState, mTransition,
mTransitionStyle, true);

 if (mAddToBackStack) {
 mManager.addBackStackState(this);
    }
}

具体仍然是调用FramentManagerImpl的对应方法。