FragmentTabHost中切换Fragment状态保存的几种方法

1.重写FragmentTabHost类

FragmentTabHost不保存状态时因为切换Fragment时使用detach和attach来隐藏和显示Fragment的，所以导致每次切换都会重新CreateView，我们可以重写FragmentTabHost类，将其中的detach和attach方法替换为hide和show，这样就可以保存状态了。

FragmentTabHost类：

import java.util.ArrayList;import android.content.Context;import android.content.res.TypedArray;import android.os.Bundle;import android.os.Parcel;import android.os.Parcelable;import android.support.v4.app.Fragment;import android.support.v4.app.FragmentManager;import android.support.v4.app.FragmentTransaction;import android.util.AttributeSet;import android.view.View;import android.view.ViewGroup;import android.widget.FrameLayout;import android.widget.LinearLayout;import android.widget.TabHost;import android.widget.TabWidget;/** * Special TabHost that allows the use of {@link Fragment} objects for its tab * content. When placing this in a view hierarchy, after inflating the hierarchy * you must call {@link #setup(Context, FragmentManager, int)} to complete the * initialization of the tab host. *  * <p> * Here is a simple example of using a FragmentTabHost in an Activity: *  * {@sample * development/samples/Support4Demos/src/com/example/android/supportv4/app/ * FragmentTabs.java complete} *  * <p> * This can also be used inside of a fragment through fragment nesting: *  * {@sample * development/samples/Support4Demos/src/com/example/android/supportv4/app/ * FragmentTabsFragmentSupport.java complete} */public class FragmentTabHost extends TabHost implementsTabHost.OnTabChangeListener {private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();private FrameLayout mRealTabContent;private Context mContext;private FragmentManager mFragmentManager;private int mContainerId;private TabHost.OnTabChangeListener mOnTabChangeListener;private TabInfo mLastTab;private boolean mAttached;static final class TabInfo {private final String tag;private final Class<?> clss;private final Bundle args;private Fragment fragment;TabInfo(String _tag, Class<?> _class, Bundle _args) {tag = _tag;clss = _class;args = _args;}}static class DummyTabFactory implements TabHost.TabContentFactory {private final Context mContext;public DummyTabFactory(Context context) {mContext = context;}@Overridepublic View createTabContent(String tag) {View v = new View(mContext);v.setMinimumWidth(0);v.setMinimumHeight(0);return v;}}static class SavedState extends BaseSavedState {String curTab;SavedState(Parcelable superState) {super(superState);}private SavedState(Parcel in) {super(in);curTab = in.readString();}@Overridepublic void writeToParcel(Parcel out, int flags) {super.writeToParcel(out, flags);out.writeString(curTab);}@Overridepublic String toString() {return "FragmentTabHost.SavedState{"+ Integer.toHexString(System.identityHashCode(this))+ " curTab=" + curTab + "}";}public static final Parcelable.Creator<SavedState> CREATOR = new Parcelable.Creator<SavedState>() {public SavedState createFromParcel(Parcel in) {return new SavedState(in);}public SavedState[] newArray(int size) {return new SavedState[size];}};}public FragmentTabHost(Context context) {// Note that we call through to the version that takes an AttributeSet,// because the simple Context construct can result in a broken object!super(context, null);initFragmentTabHost(context, null);}public FragmentTabHost(Context context, AttributeSet attrs) {super(context, attrs);initFragmentTabHost(context, attrs);}private void initFragmentTabHost(Context context, AttributeSet attrs) {TypedArray a = context.obtainStyledAttributes(attrs,new int[] { android.R.attr.inflatedId }, 0, 0);mContainerId = a.getResourceId(0, 0);a.recycle();super.setOnTabChangedListener(this);}private void ensureHierarchy(Context context) {// If owner hasn't made its own view hierarchy, then as a convenience// we will construct a standard one here.if (findViewById(android.R.id.tabs) == null) {LinearLayout ll = new LinearLayout(context);ll.setOrientation(LinearLayout.VERTICAL);addView(ll, new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.MATCH_PARENT));TabWidget tw = new TabWidget(context);tw.setId(android.R.id.tabs);tw.setOrientation(TabWidget.HORIZONTAL);ll.addView(tw, new LinearLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.WRAP_CONTENT, 0));FrameLayout fl = new FrameLayout(context);fl.setId(android.R.id.tabcontent);ll.addView(fl, new LinearLayout.LayoutParams(0, 0, 0));mRealTabContent = fl = new FrameLayout(context);mRealTabContent.setId(mContainerId);ll.addView(fl, new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 0, 1));}}/** * @deprecated Don't call the original TabHost setup, you must instead call *             {@link #setup(Context, FragmentManager)} or *             {@link #setup(Context, FragmentManager, int)}. */@Override@Deprecatedpublic void setup() {throw new IllegalStateException("Must call setup() that takes a Context and FragmentManager");}public void setup(Context context, FragmentManager manager) {ensureHierarchy(context); // Ensure views required by super.setup()super.setup();mContext = context;mFragmentManager = manager;ensureContent();}public void setup(Context context, FragmentManager manager, int containerId) {ensureHierarchy(context); // Ensure views required by super.setup()super.setup();mContext = context;mFragmentManager = manager;mContainerId = containerId;ensureContent();mRealTabContent.setId(containerId);// We must have an ID to be able to save/restore our state. If// the owner hasn't set one at this point, we will set it ourself.if (getId() == View.NO_ID) {setId(android.R.id.tabhost);}}private void ensureContent() {if (mRealTabContent == null) {mRealTabContent = (FrameLayout) findViewById(mContainerId);if (mRealTabContent == null) {throw new IllegalStateException("No tab content FrameLayout found for id "+ mContainerId);}}}@Overridepublic void setOnTabChangedListener(OnTabChangeListener l) {mOnTabChangeListener = l;}public void addTab(TabHost.TabSpec tabSpec, Class<?> clss, Bundle args) {tabSpec.setContent(new DummyTabFactory(mContext));String tag = tabSpec.getTag();TabInfo info = new TabInfo(tag, clss, args);if (mAttached) {// If we are already attached to the window, then check to make// sure this tab's fragment is inactive if it exists. This shouldn't// normally happen.info.fragment = mFragmentManager.findFragmentByTag(tag);if (info.fragment != null && !info.fragment.isDetached()) {FragmentTransaction ft = mFragmentManager.beginTransaction();//ft.detach(info.fragment);ft.hide(info.fragment);ft.commit();}}mTabs.add(info);addTab(tabSpec);}@Overrideprotected void onAttachedToWindow() {super.onAttachedToWindow();String currentTab = getCurrentTabTag();// Go through all tabs and make sure their fragments match// the correct state.FragmentTransaction ft = null;for (int i = 0; i < mTabs.size(); i++) {TabInfo tab = mTabs.get(i);tab.fragment = mFragmentManager.findFragmentByTag(tab.tag);//if (tab.fragment != null && !tab.fragment.isDetached()) {if (tab.fragment != null) {if (tab.tag.equals(currentTab)) {// The fragment for this tab is already there and// active, and it is what we really want to have// as the current tab. Nothing to do.mLastTab = tab;} else {// This fragment was restored in the active state,// but is not the current tab. Deactivate it.if (ft == null) {ft = mFragmentManager.beginTransaction();}//ft.detach(tab.fragment);ft.hide(tab.fragment);}}}// We are now ready to go. Make sure we are switched to the// correct tab.mAttached = true;ft = doTabChanged(currentTab, ft);if (ft != null) {ft.commit();mFragmentManager.executePendingTransactions();}}@Overrideprotected void onDetachedFromWindow() {super.onDetachedFromWindow();mAttached = false;}@Overrideprotected Parcelable onSaveInstanceState() {Parcelable superState = super.onSaveInstanceState();SavedState ss = new SavedState(superState);ss.curTab = getCurrentTabTag();return ss;}@Overrideprotected void onRestoreInstanceState(Parcelable state) {SavedState ss = (SavedState) state;super.onRestoreInstanceState(ss.getSuperState());setCurrentTabByTag(ss.curTab);}@Overridepublic void onTabChanged(String tabId) {if (mAttached) {FragmentTransaction ft = doTabChanged(tabId, null);if (ft != null) {ft.commit();}}if (mOnTabChangeListener != null) {mOnTabChangeListener.onTabChanged(tabId);}}private FragmentTransaction doTabChanged(String tabId,FragmentTransaction ft) {TabInfo newTab = null;for (int i = 0; i < mTabs.size(); i++) {TabInfo tab = mTabs.get(i);if (tab.tag.equals(tabId)) {newTab = tab;}}if (newTab == null) {throw new IllegalStateException("No tab known for tag " + tabId);}if (mLastTab != newTab) {if (ft == null) {ft = mFragmentManager.beginTransaction();}if (mLastTab != null) {if (mLastTab.fragment != null) {//将detach替换为hide，隐藏Fragment//ft.detach(mLastTab.fragment);ft.hide(mLastTab.fragment);}}if (newTab != null) {if (newTab.fragment == null) {newTab.fragment = Fragment.instantiate(mContext,newTab.clss.getName(), newTab.args);ft.add(mContainerId, newTab.fragment, newTab.tag);} else {//将attach替换为show，显示Fragment//ft.attach(newTab.fragment);ft.show(newTab.fragment);}}mLastTab = newTab;}return ft;}}

主Acitivity布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#eee"    android:orientation="vertical" >        <FrameLayout        android:id="@+id/realtabcontent"        android:layout_width="fill_parent"        android:layout_height="0dp"        android:layout_weight="1" />                <com.test.activity.fragment.FragmentTabHost        android:id="@android:id/tabhost"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:background="#eee" >                <FrameLayout             android:id="@android:id/tabcontent"            android:layout_width="0dp"            android:layout_height="0dp"            android:layout_weight="0" />           </com.test.activity.fragment.FragmentTabHost>     </LinearLayout>

在FragmentActivity中使用：

private void initTab() {mTabHost = (FragmentTabHost)this.findViewById(android.R.id.tabhost);mTabHost.setup(this, getSupportFragmentManager(), R.id.realtabcontent);View tabView = View.inflate(getApplicationContext(), R.layout.tab_item, null);//指定一个视图作为标签指示TabSpec tabSpec = mTabHost.newTabSpec("首页").setIndicator(tabView);ImageView tabImg = (ImageView)tabView.findViewById(R.id.main_tab_imageview);tabImg.setImageResource(R.drawable.tab_home_page);TextView tabText = (TextView)tabView.findViewById(R.id.main_tab_textview);tabText.setText("首页");mTabHost.addTab(tabSpec, HomePageFragment.class, null);tabView = View.inflate(getApplicationContext(), R.layout.tab_item, null);tabSpec = mTabHost.newTabSpec("商品").setIndicator(tabView);tabImg = (ImageView)tabView.findViewById(R.id.main_tab_imageview);tabImg.setImageResource(R.drawable.tab_goods);tabText = (TextView)tabView.findViewById(R.id.main_tab_textview);tabText.setText("商品");mTabHost.addTab(tabSpec, GoodsFragment.class, null);tabView = View.inflate(getApplicationContext(), R.layout.tab_item, null);tabSpec = mTabHost.newTabSpec("购物车").setIndicator(tabView);tabImg = (ImageView)tabView.findViewById(R.id.main_tab_imageview);tabImg.setImageResource(R.drawable.tab_shop_cart);tabText = (TextView)tabView.findViewById(R.id.main_tab_textview);tabText.setText("购物车");mTabHost.addTab(tabSpec, ShopCartFragment.class, null);tabView = View.inflate(getApplicationContext(), R.layout.tab_item, null);tabSpec = mTabHost.newTabSpec("我的").setIndicator(tabView);tabImg = (ImageView)tabView.findViewById(R.id.main_tab_imageview);tabImg.setImageResource(R.drawable.tab_mine);tabText = (TextView)tabView.findViewById(R.id.main_tab_textview);tabText.setText("我的");mTabHost.addTab(tabSpec, MineFragment.class, null);}

2.缓存Fragment中的View

在Fragment子类中加入一个成员变量，用来保存onCreateView中将要返回的View，当每次重绘时判断此成员变量是否为空，为空的时候重绘此页面，否则返回此成员变量（这个办法可以选择性地保存不同Fragment切换状态）。

@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {if(mView == null) {mView = inflater.inflate(R.layout.fragment_mine, container, false);init();}//判断是否已经被加过parent， 如果有parent需要从parent删除，要不然会发生这个rootview已经有parent的错误。ViewGroup parent = (ViewGroup)mView.getParent();if(parent != null) {parent.removeView(mView);}return mView;}