FragmentTabHost+Fragment+Viewpage遇到的Fragment重复加载问题

一、在开发App需到底部Tab切换页面，并能通过手势左右滑动切换的功能时（类似于微细Android版本的效果），在开发过程首页展示的fragment页面需要嵌入地图，也就是说把地图放到一个Fragment里面，还要支持切换，遇到地图上的Marker总是无法打上，所有的地图设置都不起作用，当切换地图时，地图数据不保存等一系列问题，通过在网上搜索和摸索现在把所有的问题总结一下。

导致这种情况的元凶就fragment多次创建实例的问题，在使用FragmentTabHost+Fragment+Viewpage时一其有两个地方法需要引用到Framgent这个类：

1、在FragmentTabHost中增加选项卡时：

public void addTab(TabHost.TabSpec tabSpec, Class<?> clss, Bundle args) {

}

第二个参数是Class类型，即传入Fragment.class(),在调用.class()方法时，fragment被实便化了一次，其生命周期方法被调用一次

2、在Viewpage中添加Fragment项时：

在些使用的FragmentStatePagerAdapter实现类

public class FragmentAdapter extends FragmentStatePagerAdapter {
    List<Fragment> fragments;
    private String[] titles = new String[]{};

    public FragmentAdapter(FragmentManager fm, List<Fragment> fragments) {
        super(fm);
        this.fragments = fragments;
    }

    @Override
    public Fragment getItem(int position) {
        return fragments.get(position);
    }

    @Override
    public int getCount() {
        return fragments == null ? 0 : fragments.size();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return titles[position];
    }
}
1、在其构造函数中有List<Fragment> fragments参数，在这里面需要传入new Fragment(),之前在调用.class已经创建一个fragment实例，但是我无法在其它容器中找到它，
所以只能new一个，这里又创建一次，导致其中元素和参数及控件都是不唯一的，所有出现了地图的设置和数据是无效的
2、在切换fragment时总是在重新走oncreateView()方法和其它生命周其方法，导致很多业务受到影响。
二、解决些问题的方向是如何做到只创建一个Fragment并切换时不走其生命周期方法：
1、修改FragmentTabHost类，保留其Tab创建和切换功能
   将之前要传入的Class只接改成Fragment例，我们是能做到Fragment只new一次的，哈哈；
   在切换时是通过tag去寻找的，在原码中写的是这样，如果没有就通过反射来创建一个，这就是fragment第一次实例化的原因
   所有我修改其中的TabInfo类 
   
if (newTab.fragment == null) {
    newTab.fragment = Fragment.instantiate(mContext,
          newTab.clss.getName(), newTab.args);
    ft.add(mContainerId, newTab.fragment, newTab.tag);
2、在doTabChanged中使用的是，改成show或hide就不会重新走生命周期方法了
ft.detach(mLastTab.fragment);
//需要改成ft.hide(mLastTab.fragment);
ft.attach(mLastTab.fragment)
//需要改成ft.show(mLastTab.fragment);
最后的改造代码如下：
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.util.Log;
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 Bundle args;
        private final Fragment fragment;

        TabInfo(String _tag,Fragment _fragment, Bundle _args) {
            tag = _tag;
            args = _args;
            fragment = _fragment;
        }
    }

    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.FILL_PARENT,
                    ViewGroup.LayoutParams.FILL_PARENT));

            TabWidget tw = new TabWidget(context);
            tw.setId(android.R.id.tabs);
            tw.setOrientation(TabWidget.HORIZONTAL);
            ll.addView(tw, new LinearLayout.LayoutParams(
                    ViewGroup.LayoutParams.FILL_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.FILL_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, Fragment fragment, Bundle args) {
        tabSpec.setContent(new DummyTabFactory(mContext));
        String tag = tabSpec.getTag();

        TabInfo info = new TabInfo(tag, fragment, args);

        mTabs.add(info);
        addTab(tabSpec);
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
    }

    @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) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }
        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.hide(mLastTab.fragment);
                }
            }
            if (newTab != null) {
                if (null == mFragmentManager.getFragments() || !mFragmentManager.getFragments().contains(newTab.fragment)) {
                    ft.add(mContainerId, newTab.fragment, newTab.tag);
                } else {
                    ft.show(newTab.fragment);
                }
            }

            mLastTab = newTab;
        }
        return ft;
    }
}

三、最后是使用高德地图在切换时黑屏问题
1、使用com.amap.api.maps.TextureSupportMapFragment即可解决
2、由于地图是可滑动的，这样就和viewpage产生了冲突，重写ViewPage即可，寻找到可滚动的View，然后将事件拦截就可完美运行了。
public class ViewPagerCompat extends ViewPager {

    public ViewPagerCompat(Context context) {
        super(context);
    }

    public ViewPagerCompat(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected boolean canScroll(View v, boolean checkV, int dx, int x, int y) {
        if(v.getClass().getName().contains("com.amap.api")) {
            return true;
        }
        return super.canScroll(v, checkV, dx, x, y);
    }
}