1.概述
上一篇博客已经简单的讲了一下Fragment的使用并写了一个基本的实例，接下来就将其整合到项目中。附视频地址：http://pan.baidu.com/s/1mhUus56
这里写图片描述
2．效果实现
列表和轮播条不做过多的解释就是访问接口获取数据而已，这个在Android Studio自定义模板和Android无限广告轮播都讲过了。我们直接整合进去这个时候我们发现一个奇怪的问题，就是切换之后会去重新加载数据很不正常。
一般的思路我们会换实现方法，当然其他方式肯定也可以实现如ViewPager+Fragment但是我们需要预加载要不然也会出问题，一旦预加载就需要去访问网络，即使用户可能不切换Fragment就退出App了这个时候其实加载了所有Fragment的数据，而且主页一旦复杂有可能会崩溃或造成内存溢出的问题。
我的签名就是，忘记不了铭记，坚持不了放弃，但只要活着... 既然这样我必须得看看源码：
2.2 Fragment源码分析：
把一个Fragment加到ViewGroup中就这么几行代码：add(@IdRes int containerViewId, Fragment fragment)和commit()，就这么两个方法：
@Override
protected void initData() {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
mHomeFragment = new HomeFragment();
fragmentTransaction.add(R.id.main_tab_fl, mHomeFragment);
fragmentTransaction.commit();
} 我们点击add方法发现是个抽象方法：
/**
* Calls {@link #add(int, Fragment, String)} with a null tag.
*/
public abstract FragmentTransaction add(@IdRes int containerViewId, Fragment fragment); 点击fragmentManager.beginTransaction()发现也是一个抽象方法：
/**
* Start a series of edit operations on the Fragments associated with
* this FragmentManager.
*
* <p>Note: A fragment transaction can only be created/committed prior
* to an activity saving its state. If you try to commit a transaction
* after {@link FragmentActivity#onSaveInstanceState FragmentActivity.onSaveInstanceState()}
* (and prior to a following {@link FragmentActivity#onStart FragmentActivity.onStart}
* or {@link FragmentActivity#onResume FragmentActivity.onResume()}, you will get an error.
* This is because the framework takes care of saving your current fragments
* in the state, and if changes are made after the state is saved then they
* will be lost.</p>
*/
public abstract FragmentTransaction beginTransaction(); 所以只能点击getSupportFragmentManager()方法这个方法在FragmentActivity中：
/**
* Return the FragmentManager for interacting with fragments associated
* with this activity.
*/
public FragmentManager getSupportFragmentManager() {
return mFragments.getSupportFragmentManager();
} 一路摸索才找到这个add方法，发现并没有写注释这个google工程师有点打酱油节奏啊！只好自己来吧在需要的地方写一写。我们看下面贴出来的源码其实可以知道，add方法其实只是设置了一些必要参数，并没有做任何的处理，这也是说google为什么一定要我们不要忘记commit()的原因：
public FragmentTransaction add(int containerViewId, Fragment fragment) {
doAddOp(containerViewId, fragment, null, OP_ADD);
return this;
}
private void doAddOp(int containerViewId, Fragment fragment, String tag, int opcmd) {
fragment.mFragmentManager = mManager;
// tag可以说是唯一标识我们可以通过它从FragmentManager中找到对应的Fragment
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);
}
// 把Fragment的ContainerId和FragmentId指定为我们传递过来的布局中的ViewGroup的id。
fragment.mContainerId = fragment.mFragmentId = containerViewId;
}
// 见名思意 Op是什么？就当是一些基本参数吧
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++;
} 既然add方法只是设置了一些参数而已，那么肯定就在commit()中做了些什么，找啊找啊找啊找，找到这么个方法（有些代码我就省略）：
void moveToState(Fragment f, int newState, int transit,
int transitionStyle, boolean keepActive){
// ... 省略部分代码
f.onAttach(mHost.getContext());
// 这个方法一调用就会执行Fragment的onAttach(Activity activity)这个生命周期方法
if (f.mParentFragment == null) {
mHost.onAttachFragment(f);
}
if (!f.mRetaining) {
f.performCreate(f.mSavedFragmentState);
// 执行生命周期onCreate(savedInstanceState);
}
f.mRetaining = false;
if (f.mFromLayout) {
ViewGroup container = null;
if (f.mContainerId != 0) {
//从activity中找到我们需要存放Fragment的ViewGroup布局
container = (ViewGroup)mContainer.onFindViewById(f.mContainerId);
if (container == null && !f.mRestored) {
throwException(new IllegalArgumentException(
"No view found for id 0x"
+ Integer.toHexString(f.mContainerId) + " ("
+ f.getResources().getResourceName(f.mContainerId)
+ ") for fragment " + f));
}
}
// 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);
// 这个方法过后会执行onCreateView()生命周期且f.mView就是我们自己覆盖Fragment返回的View
if (f.mView != null) {
f.mInnerView = f.mView;
// v4包兼容11以下的版本我还是没说错啊
if (Build.VERSION.SDK_INT >= 11) {
ViewCompat.setSaveFromParentEnabled(f.mView, false);
} else {
f.mView = NoSaveStateFrameLayout.wrap(f.mView);
}
if (container != null) {
Animation anim = loadAnimation(f, transit, true,
transitionStyle);
if (anim != null) {
setHWLayerAnimListenerIfAlpha(f.mView, anim);
f.mView.startAnimation(anim);
}
// 如果ViewGroup不等于null就把从onCreateView()生命周期中获得的View添加到该布局中
// 最主要的就是这个方法，其实我们可以把Fragment理解成一个自定义的类
// 通过onCreateView()获取的到View添加到一个FragmentActivity的一个ViewGroup中
// 只不过它有自己的生命周期而已......
container.addView(f.mView);
}
// 如果是隐藏那就设置为不可见
if (f.mHidden) f.mView.setVisibility(View.GONE);
// 执行onViewCreated()生命周期方法
f.onViewCreated(f.mView, f.mSavedFragmentState);
} else {
f.mInnerView = null;
}
f.performActivityCreated(f.mSavedFragmentState);
if (f.mView != null) {
f.restoreViewState(f.mSavedFragmentState);
}
f.mSavedFragmentState = null;
}
// 代码省略......
}
}
// 后面的我们就不看了，这上面的代码我自己做了一些整合，把它连贯起来了
// 因为我们把add方法写在了Activity中的onCreate()方法中所以做了一些处理...... 到这里应该能够了解Fragment的工作流程了吧，接下来我们看replace方法中究竟做了？其实和add差不多只是把int opcmd变成了OP_REPLACE替换操作：
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;
} 这个时候去commit会调用mManager.removeFragment(old, transition, transitionStyle)方法把原来的移除，然后把当前的Fragment添加进去，那岂不是每点击一个上一就被销毁了，那之前华东到哪里来了做了写什么事都被干掉重新创建了。
if (mManager.mAdded != null) {
for (int i = mManager.mAdded.size() - 1; i >= 0; i--) {
Fragment old = mManager.mAdded.get(i);
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;
}
mManager.removeFragment(old, transition, transitionStyle);
}
}
}
}
if (f != null) {
f.mNextAnim = enterAnim;
mManager.addFragment(f, false);
} 
这里写图片描述
到这里源码就以完毕有兴趣的小伙伴可以自己仔细去看看源码，接下来我们就来解决问题，我们肯定在调用replace方法的时候希望它不要移除原来的，那怎么办改Android的底层源码吗？那就只能换方法了，思路就是如果该Fragment不存在FragmentManager中我们就去添加，否则我们把之前的隐藏而不是替换移除，把当前的显示即可，最后代码就是：
private void homeRbClick() {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
List<Fragment> fragments = fragmentManager.getFragments();
for (Fragment fragment : fragments) {
fragmentTransaction.hide(fragment);
}
fragmentTransaction.show(mHomeFragment);
fragmentTransaction.commit();
}
@OnClick(R.id.find_rb)
private void findRbClick() {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
List<Fragment> fragments = fragmentManager.getFragments();
for (Fragment fragment : fragments) {
fragmentTransaction.hide(fragment);
}
if(mFindFragment == null){
mFindFragment = new FindFragment();
fragmentTransaction.add(R.id.main_tab_fl,mFindFragment);
}else {
fragmentTransaction.show(mFindFragment);
}
fragmentTransaction.commit();
}
@OnClick(R.id.new_rb)
private void newRbClick() {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
List<Fragment> fragments = fragmentManager.getFragments();
for (Fragment fragment : fragments) {
fragmentTransaction.hide(fragment);
}
if(mNewFragment == null){
mNewFragment = new NewFragment();
fragmentTransaction.add(R.id.main_tab_fl,mNewFragment);
}else {
fragmentTransaction.show(mNewFragment);
}
fragmentTransaction.commit();
}
@OnClick(R.id.message_rb)
private void messageRbClick() {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
List<Fragment> fragments = fragmentManager.getFragments();
for (Fragment fragment : fragments) {
fragmentTransaction.hide(fragment);
}
if(mMessageFragment == null){
mMessageFragment = new MessageFragment();
fragmentTransaction.add(R.id.main_tab_fl,mMessageFragment);
}else {
fragmentTransaction.show(mMessageFragment);
}
fragmentTransaction.commit();
} 这里已经写得太多了视频里还做了一个代码优化，具体附视频地址：http://pan.baidu.com/s/1mhUus56
这里写图片描述
