我有一个设置标签主机的 FragmentActivity。每个选项卡都是一个简单的 Fragment，称为 TabFragment。TabFragment 有一个 ViewPager，在这种情况下它是antonyt的 InfiniteViewPager （在这里讨论：ViewPager as a circular queue / wrapping）。
（主要）问题如下：
我启动应用程序。我单击第二个选项卡。当我应该看到与第一个选项卡中相同的内容时，只有一个空白屏幕。向右滚动几次后，我确实看到了我的 TextViews。
在 ViewPagers 中滚动片段和更改选项卡最终会导致停止和 FC，而不会引发明确的异常。
这是我对 Fragments 的第一次尝试，我必须承认，我不理解观察到的行为。
任何提示将不胜感激。
整个项目都在这里。
编码：
带有 TabHost 的 FragmentActivity：
package com.example.viewpagerintab;
import java.util.HashMap;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.widget.TabHost;
import android.widget.TabHost.TabContentFactory;
public class TabsFragmentActivity extends FragmentActivity implements
TabHost.OnTabChangeListener {
private TabHost mTabHost;
private HashMap mapTabInfo = new HashMap();
private TabInfo mLastTab = null;
public TabsFragmentActivity() {
}
private class TabInfo {
private String tag;
private Class clss;
private Bundle args;
private Fragment fragment;
TabInfo(String tag, Class classObject, Bundle args) {
this.tag = tag;
this.clss = classObject;
this.args = args;
}
}
class TabFactory implements TabContentFactory {
private final Context mContext;
/**
* @param context
*/
public TabFactory(Context context) {
mContext = context;
}
/**
* (non-Javadoc)
*
* @see android.widget.TabHost.TabContentFactory#createTabContent(java.lang.String)
*/
public View createTabContent(String tag) {
View v = new View(mContext);
v.setMinimumWidth(0);
v.setMinimumHeight(0);
return v;
}
}
/**
* (non-Javadoc)
*
* @see android.support.v4.app.FragmentActivity#onCreate(android.os.Bundle)
*/
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.tabs);
initialiseTabHost(savedInstanceState);
if (savedInstanceState != null) {
mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab"));
}
}
/**
* (non-Javadoc)
*
* @see android.support.v4.app.FragmentActivity#onSaveInstanceState(android.os.Bundle)
*/
protected void onSaveInstanceState(Bundle outState) {
outState.putString("tab", mTabHost.getCurrentTabTag());
super.onSaveInstanceState(outState);
}
private void initialiseTabHost(Bundle args) {
mTabHost = (TabHost) findViewById(android.R.id.tabhost);
mTabHost.setup();
TabInfo tabInfo = null;
tabInfo = new TabInfo("Discover", TabFragmentD.class, args);
TabsFragmentActivity.addTab(this, mTabHost,
mTabHost.newTabSpec("Discover").setIndicator("Discover"),
tabInfo);
mapTabInfo.put(tabInfo.tag, tabInfo);
tabInfo = new TabInfo("Friends", TabFragmentF.class, args);
TabsFragmentActivity
.addTab(this, mTabHost, mTabHost.newTabSpec("Friends")
.setIndicator("Friends"), tabInfo);
mapTabInfo.put(tabInfo.tag, tabInfo);
onTabChanged("Discover");
mTabHost.setOnTabChangedListener(this);
}
/**
* @param activity
* @param tabHost
* @param tabSpec
* @param clss
* @param args
*/
private static void addTab(TabsFragmentActivity activity, TabHost tabHost,
TabHost.TabSpec tabSpec, TabInfo tabInfo) {
// Attach a Tab view factory to the spec
tabSpec.setContent(activity.new TabFactory(activity));
String tag = tabSpec.getTag();
// Check to see if we already have a fragment for this tab, probably
// from a previously saved state. If so, deactivate it, because our
// initial state is that a tab isn't shown.
tabInfo.fragment = activity.getSupportFragmentManager()
.findFragmentByTag(tag);
if (tabInfo.fragment != null && !tabInfo.fragment.isDetached()) {
FragmentTransaction ft = activity.getSupportFragmentManager()
.beginTransaction();
ft.detach(tabInfo.fragment);
ft.commit();
activity.getSupportFragmentManager().executePendingTransactions();
}
tabHost.addTab(tabSpec);
}
/**
* (non-Javadoc)
*
* @see android.widget.TabHost.OnTabChangeListener#onTabChanged(java.lang.String)
*/
public void onTabChanged(String tag) {
TabInfo newTab = mapTabInfo.get(tag);
if (mLastTab != newTab) {
FragmentTransaction ft = getSupportFragmentManager()
.beginTransaction();
if (mLastTab != null) {
if (mLastTab.fragment != null) {
ft.detach(mLastTab.fragment);
}
}
if (newTab != null) {
if (newTab.fragment == null) {
newTab.fragment = Fragment.instantiate(this,
newTab.clss.getName(), newTab.args);
ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
} else {
ft.attach(newTab.fragment);
}
}
mLastTab = newTab;
ft.commit();
getSupportFragmentManager().executePendingTransactions();
}
}
}
TabFragment 包含 InfiniteViewPager：
package com.example.viewpagerintab;
import java.util.List;
import java.util.Vector;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import com.antonyt.infiniteviewpager.InfinitePagerAdapter;
import com.example.viewpagerintab.pager.SimpleAdapter;
public class TabFragment extends Fragment {
private static final String TAG = TabFragment.class.getSimpleName();
protected View mView;
ViewPager mViewPager;
private InfinitePagerAdapter mPagerAdapter;
PageListener pageListener;
public TabFragment() {
}
/**
* (non-Javadoc)
*
* @see android.support.v4.app.Fragment#onCreateView(android.view.LayoutInflater,
* android.view.ViewGroup, android.os.Bundle)
*/
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Log.d(TAG, "onCreateView - called");
if (container == null) {
// We have different layouts, and in one of them this
// fragment's containing frame doesn't exist. The fragment
// may still be created from its saved state, but there is
// no reason to try to create its view hierarchy because it
// won't be displayed. Note this is not needed -- we could
// just run the code below, where we would create and return
// the view hierarchy; it would just never be used.
return null;
}
pageListener = new PageListener();
mView = (LinearLayout) inflater.inflate(R.layout.tab, container, false);
List fragments = new Vector();
fragments.add(DayFragment.newInstance("one"));
fragments.add(DayFragment.newInstance("two"));
fragments.add(DayFragment.newInstance("three"));
fragments.add(DayFragment.newInstance("four"));
mPagerAdapter = new InfinitePagerAdapter(
new com.example.viewpagerintab.PagerAdapter(
getFragmentManager(), fragments));
mViewPager = (ViewPager) mView.findViewById(R.id.viewpager);
mViewPager.setOnPageChangeListener(pageListener);
new setAdapterTask().execute();
Log.d(TAG, "onCreateView - finished");
return mView;
}
private class setAdapterTask extends AsyncTask {
protected Void doInBackground(Void... params) {
return null;
}
@Override
protected void onPostExecute(Void result) {
mViewPager.setAdapter(mPagerAdapter);
}
}
class PageListener implements OnPageChangeListener {
private final String TAG = PageListener.class.getSimpleName();
@Override
public void onPageScrollStateChanged(int arg0) {
Log.d(TAG, "onPageScrollStateChanged(..) to: " + arg0);
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
// Log.d(TAG, "onPageScrolled(..) - called");
}
@Override
public void onPageSelected(int arg0) {
Log.d(TAG, "onPageSelected(..) selected: " + arg0);
}
}
}
TabFragmentD 和 TabFragmentF 几乎相同：
public class TabFragmentD extends TabFragment {
public TabFragmentD() {
}
}
DayFragment 只包含一个 TextView：
package com.example.viewpagerintab;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
public class DayFragment extends Fragment {
private static final String TAG = DayFragment.class.getSimpleName();
protected View mView;
protected TextView tvDay;
public DayFragment() {
}
/**
* (non-Javadoc)
*
* @see android.support.v4.app.Fragment#onCreateView(android.view.LayoutInflater,
* android.view.ViewGroup, android.os.Bundle)
*/
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (container == null) {
// We have different layouts, and in one of them this
// fragment's containing frame doesn't exist. The fragment
// may still be created from its saved state, but there is
// no reason to try to create its view hierarchy because it
// won't be displayed. Note this is not needed -- we could
// just run the code below, where we would create and return
// the view hierarchy; it would just never be used.
return null;
}
mView = (LinearLayout) inflater.inflate(R.layout.day, container, false);
tvDay = (TextView) mView.findViewById(R.id.tvText);
String text = getArguments().getString("text");
Log.d(TAG, "creating view with text: " + text);
tvDay.setText(text);
return mView;
}
public static DayFragment newInstance(String text) {
Log.d(TAG, "newInstance with text: " + text);
DayFragment f = new DayFragment();
// Supply text input as an argument.
Bundle args = new Bundle();
args.putString("text", text);
f.setArguments(args);
return f;
}
}
寻呼机适配器：
package com.example.viewpagerintab;
import java.util.List;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
public class PagerAdapter extends FragmentPagerAdapter {
private List fragments;
public PagerAdapter(FragmentManager fm, List fragments) {
super(fm);
this.fragments = fragments;
}
/*
* (non-Javadoc)
*
* @see android.support.v4.app.FragmentPagerAdapter#getItem(int)
*/
@Override
public Fragment getItem(int position) {
return fragments.get(position);
}
/*
* (non-Javadoc)
*
* @see android.support.v4.view.PagerAdapter#getCount()
*/
@Override
public int getCount() {
return this.fragments.size();
}
}
InfiniteViewPager 和 InfinitePageAdapter 在antonyt 的 github 上。
选项卡.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TabHost
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0"
android:orientation="horizontal" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="0" />
<FrameLayout
android:id="@+android:id/realtabcontent"
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="1" />
</LinearLayout>
</TabHost>
</LinearLayout>
选项卡.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@android:color/black" >
<com.antonyt.infiniteviewpager.InfiniteViewPager
android:id="@+android:id/viewpager"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
</LinearLayout>
日.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@android:color/black"
android:gravity="center" >
<TextView
android:id="@+id/tvText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/white" />
</LinearLayout>
更新
正如 CommonsWare 所指出的，Android 在 Fragments 中的 Fragments 存在问题。
我将 tabs.xml 修改为：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TabHost
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0"
android:orientation="horizontal" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="0" />
<FrameLayout
android:id="@+android:id/realtabcontent"
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="0" />
<com.antonyt.infiniteviewpager.InfiniteViewPager
android:id="@+android:id/viewpager"
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="1" />
</LinearLayout>
</TabHost>
</LinearLayout>
并创建了空的 TabFragments (tab.xml)：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="0dp"
android:layout_height="0dp" >
</LinearLayout>
所以现在切换标签几乎与滑动无关。
唯一的缺点是，在更改选项卡后将 ViewPager 的当前位置设置为 0 的任何尝试都存在一个非常烦人的问题（应用程序毫无例外地崩溃了）。