Question

I am implementing nested fragments in my app using the new API 17, which provides a FragmentTabHost for doing so. However, I’m having trouble with a few basic things for my simple 2 tab fragments inside a parent fragment:

1. I would like the nested tabs to be at the bottom (View1 and View2 tabs)
2. I would like to customize the actual tabs to look different than standard

Has anyone worked with these before and know how to achieve this? Here’s the sample code which I have up and running:

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTabHost;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class FragmentTabsFragmentSupport extends Fragment {
private FragmentTabHost mTabHost;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    mTabHost = new FragmentTabHost(getActivity());
    mTabHost.setup(getActivity(), getChildFragmentManager(), R.id.fragment1);

    mTabHost.addTab(mTabHost.newTabSpec("Tab1").setIndicator("Simple"),
            NestedFragment1.class, null);
    mTabHost.addTab(mTabHost.newTabSpec("Tab2").setIndicator("Contacts"),
            NestedFragment2.class, null);

    return mTabHost;
}

@Override
public void onDestroyView() {
    super.onDestroyView();
    mTabHost = null;
}
}

I have tried the following to bottom align the tabs, but no luck:

TabWidget mTabWidget = mTabHost.getTabWidget();
mTabWidget.setGravity(Gravity.BOTTOM);
mTabWidget.setVerticalGravity(Gravity.BOTTOM);

Answer 1

I finally got to the bottom of this. There is an issue with FragmentTabHost.java which will always create a TabHost element for you, no matter what you define in XML and inflate beforehand.

As such, I commented out that part of code when writing my own version of FragmentTabHost.java.

Make sure to use your new version of this in your XML layout, <com.example.app.MyFragmentTabHost

And of course inflate it:

Fragment1.java:

mTabHost = (MyFragmentTabHost) view.findViewById(android.R.id.tabhost);
mTabHost.setup(getActivity(), getChildFragmentManager(), android.R.id.tabcontent);

MyFragmentTabHost.java:

package com.example.app;

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.widget.FrameLayout;
import android.widget.TabHost;

/**
 * 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.
 *
 */
public class MyFragmentTabHost 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 MyFragmentTabHost(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 MyFragmentTabHost(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);


    /*** REMOVE THE REST OF THIS FUNCTION ***/
    /*** findViewById(android.R.id.tabs) IS NULL EVERY TIME ***/
}

/**
 * @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) {
    super.setup();
    mContext = context;
    mFragmentManager = manager;
    ensureContent();
}

public void setup(Context context, FragmentManager manager, int containerId) {
    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.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.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);
            }
        }
    }

    // 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);
            }
        }
        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);
            }
        }

        mLastTab = newTab;
    }
    return ft;
}
}