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 implements
		TabHost.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;
		}

		@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 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
	@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(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);
	}

	@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) {
					//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)。

@Override
	public 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;
	}


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