使用选项卡TabWidget与TabHost实现底部或者顶部四个分类按钮 点击切换对应的fragment

         首先作为一名菜鸟，尤其是记忆不好菜鸟，主动手写笔记记忆一些东西还是很有必要的，至少对于我而言。

言归正传，首先当大家看到这个需求，会想到布局中的选项卡控件，TabHost与TabWidget，其中这两个的区别，我的理解就是TabHost是装有选项卡+选项卡内容（FrameLayout）的容器，而TabWidget则就是底部或者顶部的那四个按钮。

再说布局中的注意事项的时候首先我们先看下布局，我这里只列出常用的这个方法

注意事项： 如上图，我已经用红线标注出来（网上有很多的总结，这里我自己再总结下，便于以后自己查看），首先

1、注意控件的顺序（FrameLayout与TabWidget顺序可变）。

2、FrameLayout、TabWidget这2个布局控件的id是系统定义好的，不能变，如图红框里的。其中TabHost控件id可使用系统定义好的，也可以自己定义。

3、在使用LinearLayout包裹FrameLayout与TabWidget时，若想实现四个Tab位于底部（默认是顶部），那么必须在FrameLayout中添加属性android：layout_weight="1"。若使用RelativeLayout包裹，则需要在TabWidget控件中添加属性android:layout_alignParentBottom="true"。其他的情况也没试过，这两种就是这样子，要问为什么这么做，大家可以试一下，实践证明就是这样子☺。

这些是布局中的一些问题，大家若是还有补充的或者发现我哪里有错误，欢迎大家补充并指出来，本菜鸟有错必改(*^__^*) 嘻嘻。

在实际开发中，我们会发现切换tab时会出现fagment重建，为了避免这种情况，这里给出一种方法，也是我们项目中用到：重写了控件TabHost

public class TabFragmentHost 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 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 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 Creator<SavedState> CREATOR = new Creator<SavedState>() {public SavedState createFromParcel(Parcel in) {return new SavedState(in);}public SavedState[] newArray(int size) {return new SavedState[size];}};}public TabFragmentHost(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 TabFragmentHost(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 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(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) {// 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 {// ft.attach(newTab.fragment);ft.show(newTab.fragment);}}mLastTab = newTab;}return ft;}}

代码有点多，其实与原类差不多，只是将attach与dettach方法改为show和hide，防止切换tab导致fragment重建。

在实际开发中（本例子在Activity中所要注意的）

private int[] tabImgRes;private Class[] fragments;private String[] tabTags;

1、若是不继承TabActivity，则不要忘记在Activity首先要调用mFragmentTabHost.setup()方法，我们上面的代码是重写了setup方法。

2、mFragmentTabHost.addTab（spec）将每个tab添加到TabHost中（实际开发中，一个for循环即可），我们上面的代码是重写了addTab方法（

for (int i = 0; i < fragments.length; i++) {    tabFragmentHost.addTab(tabFragmentHost.newTabSpec(tabTags[i]).setIndicator(getTab(i)), fragments[i], bundle);}

）。

3、若是处理点击tab事件，直接调用mFragmentTabHost.setOnTabChangedListener即可。

4、获取当前tab

public int getCurrentTabIndex() {        return tabFragmentHost.getCurrentTab();    }

5、切换相应的fragment

public void switchToIndex(int index) {        tabFragmentHost.setCurrentTab(index - 1);    }

6、getTab（int i）方法返回一个view作为setIndicator中的参数

private View getTab(int i) {        View view = getLayoutInflater().inflate(R.layout.item_main_tab, null);        TextView mainTextView = (TextView) view.findViewById(R.id.mainTextView);        mainTextView.setText(tabTags[i]);        ImageView img = (ImageView) view.findViewById(R.id.img);        img.setImageResource(tabImgRes[i]);          return view;    }

最后附上关于TabWidget android中文API来自点击打开链接
以上就是此次的笔记，同样希望能帮助到其他人，文中有错的或者需要补充的，请多多指出。