Martin.Mu `s Special Column
前言
最近在研究Glide的時候，發現Glide的with方法的主要目的是想將圖片的加載於傳入的Activity/Fragment的生命週期進行繫結,發現他的思路很巧妙，是通過新增Fragment的方法進行圖片下載的管理,在這裡我將Glide中使用的一些方法和我們常用的Fragment的Api進行學習記錄,針對他的replace,attach,detach,add,show,hide方法做了生命週期的驗證，以及一些相關的原始碼片段解析，希望對各位也有幫助。
準備工作
專案程式碼
結構圖
這張類結構圖是我看原始碼的時候畫出來的，方便我對原始碼的理解,畫得不好的地方歡迎指出。
由於版本的原始碼會經常改寫，目前8.0的原始碼版本中,Fragment的原始碼已經有改動，本人看了下，編寫過程中沒有6.0便於理解,所以該專案的原始碼解析我們就指定一個Android 6.0的原始碼來進行分析。
常用方法解析
Replace用例和解析
public class ReplaceFragmentsActivity extends AppCompatActivity {
Fragment currentFragment;
Fragment1 fragment1 = new Fragment1();
Fragment2 fragment2 = new Fragment2();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate( 可以看見他的replace方法很簡單一行程式碼替換就行，下面是他的生命週期結果圖：
看到上面的結果，我們得出以下結論：
新Fragment作為替換目標繫結到當前Activity時,原繫結的Fragment被銷燬，新的Fragment建立後被繫結到當前Activity。
原始碼解析
BackStackRecord繼承FragmentTransaction類,FragmentTransaction裡面定義了很多Fragment管理的API,我們來看下原始碼：
/**
* @hide Entry of an operation on the fragment back stack.
*/
final class BackStackRecord extends FragmentTransaction implements
FragmentManager.BackStackEntry, Runnable {
static final class Op {
Op next;
Op prev;
int cmd;
Fragment fragment;
int enterAnim;
int exitAnim;
int popEnterAnim;
int popExitAnim;
ArrayList<Fragment> removed;
}
...
public FragmentTransaction replace(int containerViewId, Fragment fragment) {
return replace(containerViewId, fragment, null);
}
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;
}
Fragment f = op.fragment;
int containerId = f.mContainerId;
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 (old.mContainerId == containerId) {
if (old == f) {
op.fragment = f = null;
} else {
if (op.removed == null) {
op.removed = new ArrayList<Fragment>();
}
op.removed.add(old);
old.mNextAnim = exitAnim;
if (mAddToBackStack) {
old.mBackStackNesting += 1;
if (FragmentManagerImpl.DEBUG) Log.v(TAG, "Bump nesting of "
+ old + " to " + old.mBackStackNesting);
}
mManager.removeFragment(old, transition, transitionStyle);
}
}
}
}
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);
}
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++;
}
...
}
可以看見我們的Op是一個內部類，結構的話是一個雙向連結串列，雙向連結串列的特性就是方便查詢，可以看見我們的Fragment的管理核心就是雙向連結串列，資料就是fragment,使用了命令模式int cmd來進行相關的操作,因為類實現了Runable方法,由於程式碼邏輯較長，一些邏輯程式碼我就不貼了，就是講op加入到連結串列中，然後遍歷加入的op呼叫當前類的加入到佇列執行我們的任務，核心的方法就是run,現在我們來看看run方法：
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);
TransitionState state = null;
SparseArray<Fragment> firstOutFragments = null;
SparseArray<Fragment> lastInFragments = null;
if (SUPPORTS_TRANSITIONS) {
firstOutFragments = new SparseArray<Fragment>();
lastInFragments = new SparseArray<Fragment>();
calculateFragments(firstOutFragments, lastInFragments);
state = beginTransition(firstOutFragments, lastInFragments, false);
}
int transitionStyle = state != null ? 0 : mTransitionStyle;
int transition = state != null ? 0 : mTransition;
Op op = mHead;
while (op != null) {
int enterAnim = state != null ? 0 : op.enterAnim;
int exitAnim = state != null ? 0 : op.exitAnim;
switch (op.cmd) {
case OP_ADD: {
Fragment f = op.fragment;
f.mNextAnim = enterAnim;
mManager.addFragment(f, false);
} break;
case OP_REPLACE: {
Fragment f = op.fragment;
int containerId = f.mContainerId;
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 (old.mContainerId == containerId) {
if (old == f) {
op.fragment = f = null;
} else {
if (op.removed == null) {
op.removed = new ArrayList<Fragment>();
}
op.removed.add(old);
old.mNextAnim = exitAnim;
if (mAddToBackStack) {
old.mBackStackNesting += 1;
if (FragmentManagerImpl.DEBUG) Log.v(TAG, "Bump nesting of "
+ old + " to " + old.mBackStackNesting);
}
mManager.removeFragment(old, transition, transitionStyle);
}
}
}
}
if (f != null) {
f.mNextAnim = enterAnim;
mManager.addFragment(f, false);
}
} break;
default: {
throw new IllegalArgumentException("Unknown cmd: " + op.cmd);
}
}
op = op.next;
}
mManager.moveToState(mManager.mCurState, transition, transitionStyle, true);
if (mAddToBackStack) {
mManager.addBackStackState(this);
}
}
}
final class FragmentManagerImpl extends FragmentManager implements LayoutInflaterFactory {
...
public void removeFragment(Fragment fragment, int transition, int transitionStyle) {
if (DEBUG) Log.v(TAG, "remove: " + fragment + " nesting=" + fragment.mBackStackNesting);
final boolean inactive = !fragment.isInBackStack();
if (!fragment.mDetached || inactive) {
if (mAdded != null) {
mAdded.remove(fragment);
}
if (fragment.mHasMenu && fragment.mMenuVisible) {
mNeedMenuInvalidate = true;
}
fragment.mAdded = false;
fragment.mRemoving = true;
moveToState(fragment, inactive ? Fragment.INITIALIZING : Fragment.CREATED,
transition, transitionStyle, false);
}
}
void moveToState(Fragment f, int newState, int transit, int transitionStyle,
boolean keepActive) {
// Fragments that are not currently added will sit in the onCreate() state.
if ((!f.mAdded || f.mDetached) && newState > Fragment.CREATED) {
newState = Fragment.CREATED;
}
if (f.mRemoving && newState > f.mState) {
// While removing a fragment, we can't change it to a higher state.
newState = f.mState;
}
// Defer start if requested; don't allow it to move to STARTED or higher
// if it's not already started.
if (f.mDeferStart && f.mState < Fragment.STARTED && newState > Fragment.STOPPED) {
newState = Fragment.STOPPED;
}
if (f.mState < newState) {
// For fragments that are created from a layout, when restoring from
// state we don't want to allow them to be created until they are
// being reloaded from the layout.
if (f.mFromLayout && !f.mInLayout) {
return;
}
if (f.mAnimatingAway != null) {
// The fragment is currently being animated... but! Now we
// want to move our state back up. Give up on waiting for the
// animation, move to whatever the final state should be once
// the animation is done, and then we can proceed from there.
f.mAnimatingAway = null;
moveToState(f, f.mStateAfterAnimating, 0, 0, true);
}
switch (f.mState) {
case Fragment.INITIALIZING:
if (DEBUG) Log.v(TAG, "moveto CREATED: " + f);
if (f.mSavedFragmentState != null) {
f.mSavedFragmentState.setClassLoader(mHost.getContext().getClassLoader());
f.mSavedViewState = f.mSavedFragmentState.getSparseParcelableArray(
FragmentManagerImpl.VIEW_STATE_TAG);
f.mTarget = getFragment(f.mSavedFragmentState,
FragmentManagerImpl.TARGET_STATE_TAG);
if (f.mTarget != null) {
f.mTargetRequestCode = f.mSavedFragmentState.getInt(
FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG, 0);
}
f.mUserVisibleHint = f.mSavedFragmentState.getBoolean(
FragmentManagerImpl.USER_VISIBLE_HINT_TAG, true);
if (!f.mUserVisibleHint) {
f.mDeferStart = true;
if (newState > Fragment.STOPPED) {
newState = Fragment.STOPPED;
}
}
}
f.mHost = mHost;
f.mParentFragment = mParent;
f.mFragmentManager = mParent != null
? mParent.mChildFragmentManager : mHost.getFragmentManagerImpl();
f.mCalled = false;
f.onAttach(mHost.getContext());
if (!f.mCalled) {
throw new SuperNotCalledException("Fragment " + f
+ " did not call through to super.onAttach()");
}
if (f.mParentFragment == null) {
mHost.onAttachFragment(f);
}
if (!f.mRetaining) {
f.performCreate(f.mSavedFragmentState);
}
f.mRetaining = false;
if (f.mFromLayout) {
// For fragments that are part of the content view
// layout, we need to instantiate the view immediately
// and the inflater will take care of adding it.
f.mView = f.performCreateView(f.getLayoutInflater(
f.mSavedFragmentState), null, f.mSavedFragmentState);
if (f.mView != null) {
f.mInnerView = f.mView;
if (Build.VERSION.SDK_INT >= 11) {
ViewCompat.setSaveFromParentEnabled(f.mView, false);
} else {
f.mView = NoSaveStateFrameLayout.wrap(f.mView);
}
if (f
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