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
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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 implements
TabHost.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;
}
@Override
public 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();
}
@Override
public void writeToParcel(Parcel out, int flags) {
super.writeToParcel(out, flags);
out.writeString(curTab);
}
@Override
public 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
@Deprecated
public 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);
}
}
}
@Override
public 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);
}
@Override
protected 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();
}
}
@Override
protected void onDetachedFromWindow() {
super.onDetachedFromWindow();
mAttached = false;
}
@Override
protected Parcelable onSaveInstanceState() {
Parcelable superState = super.onSaveInstanceState();
SavedState ss = new SavedState(superState);
ss.curTab = getCurrentTabTag();
return ss;
}
@Override
protected void onRestoreInstanceState(Parcelable state) {
SavedState ss = (SavedState) state;
super.onRestoreInstanceState(ss.getSuperState());
setCurrentTabByTag(ss.curTab);
}
@Override
public 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;
}
}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();
}
public void switchToIndex(int index) {
tabFragmentHost.setCurrentTab(index - 1);
}
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;
}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。
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