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在与实现 TabActivity 和 Fragments 和 viewPager 等选项卡的常用方法进行了一周的斗争后，我未能获得活动的实例或选项卡的片段，并且找不到解决问题的方法。所以我决定以不同的方式实现它。首先，我用一个简单的按钮制作了一个 tabWidget。在 android 开发者网站中，我找到了一种在运行时替换片段的方法。所以唯一剩下的就是如何访问选项卡片段以从我的 FragmentActivity 调用方法。

这是我使用 pageViewer 的 FragmentActivity。当我想在setup()方法中获取选项卡的片段对象时，我得到空指针：

public class MainActivity extends FragmentActivity implements
    OnTabChangeListener, OnPageChangeListener {
    private TabHost mTabHost;
private ViewPager mViewPager;
private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, MainActivity.TabInfo>();
private PagerAdapter mPagerAdapter;
private TabInfo mLastTab = null;

private class TabInfo {
    private String tag;
    private Class clss;
    private Bundle args;
    private Fragment fragment;

    TabInfo(String tag, Class clazz, Bundle args) {
        this.tag = tag;
        this.clss = clazz;
        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;
    }

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    Log.d("checking", "setup tabs...");
    setContentView(R.layout.activity_main);
    // //
    initialiseTabHost(savedInstanceState);
    if (savedInstanceState != null) {
        mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab")); 
    }
    intialiseViewPager();
    // //
    setup();
    // ///
}

protected void onSaveInstanceState(Bundle outState) {
    outState.putString("tab", mTabHost.getCurrentTabTag()); // save the tab
                                                            // selected
    super.onSaveInstanceState(outState);
}

private void intialiseViewPager() {

    List<Fragment> fragments = new Vector<Fragment>();
    fragments
            .add(Fragment.instantiate(this, CoachFragment.class.getName()));
    fragments
            .add(Fragment.instantiate(this, LogingFragment.class.getName()));
    fragments.add(Fragment.instantiate(this,
            HistoryFragment.class.getName()));
    this.mPagerAdapter = new PagerAdapter(
            super.getSupportFragmentManager(), fragments);
    //
    this.mViewPager = (ViewPager) super.findViewById(R.id.viewpager);
    this.mViewPager.setAdapter(this.mPagerAdapter);
    this.mViewPager.setOnPageChangeListener(this);
    mViewPager.setOffscreenPageLimit(1000000);
}

private void initialiseTabHost(Bundle args) {
    mTabHost = (TabHost) findViewById(android.R.id.tabhost);
    mTabHost.setup();
    mTabHost.getTabWidget().setDividerDrawable(R.drawable.tab_divider);
    TabInfo tabInfo = null;
    View tabView1 = createTabView(this, coach");
    MainActivity.AddTab(this, this.mTabHost, this.mTabHost
            .newTabSpec("Tab1").setIndicator(tabView1),
            (tabInfo = new TabInfo("Tab1", CoachFragment.class, args)));
    this.mapTabInfo.put(tabInfo.tag, tabInfo);
    View tabView2 = createTabView(this, logbook");
    MainActivity.AddTab(this, this.mTabHost, this.mTabHost
            .newTabSpec("Tab2").setIndicator(tabView2),
            (tabInfo = new TabInfo("Tab2", LogingFragment.class, args)));
    this.mapTabInfo.put(tabInfo.tag, tabInfo);
    View tabView3 = createTabView(this, "history");
    MainActivity.AddTab(this, this.mTabHost, this.mTabHost
            .newTabSpec("Tab3").setIndicator(tabView3),
            (tabInfo = new TabInfo("Tab3", HistoryFragment.class, args)));
    this.mapTabInfo.put(tabInfo.tag, tabInfo);
    mTabHost.setOnTabChangedListener(this);
}

private static void AddTab(MainActivity activity, TabHost tabHost,
        TabHost.TabSpec tabSpec, TabInfo tabInfo) {
    // Attach a Tab view factory to the spec
    tabSpec.setContent(activity.new TabFactory(activity));
    tabHost.addTab(tabSpec);
}

public void setup() {
    ....
                        CoachFragment fragment=(CoachFragment) mPagerAdapter.getRegisteredFragment(mViewPager.getCurrentItem());
                        fragment.setTempView(R.id.welcome);
                        fragment.animate();
                    ....
}

public void onTabChanged(String tag) {
    // TabInfo newTab = this.mapTabInfo.get(tag);
    int pos = this.mTabHost.getCurrentTab();
    this.mViewPager.setCurrentItem(pos);
}

private static View createTabView(final Context context, final String text) {
    View view = LayoutInflater.from(context)
            .inflate(R.layout.tabs_bg, null);
    TextView tv = (TextView) view.findViewById(R.id.tabsText);
    tv.setText(text);
    return view;
}


@Override
public void onPageScrollStateChanged(int arg0) {
    // TODO Auto-generated method stub

}

@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
    // TODO Auto-generated method stub

}

@Override
public void onPageSelected(int position) {
    // TODO Auto-generated method stub
    this.mTabHost.setCurrentTab(position);
}

}

我的页面适配器：

public class PagerAdapter extends FragmentPagerAdapter {

private List<Fragment> fragments;
private HashMap<Integer, Fragment> registeredFragments=new HashMap<Integer, Fragment>();
/**
 * @param fm
 * @param fragments
 */
public PagerAdapter(FragmentManager fm, List<Fragment> fragments) {
    super(fm);
    this.fragments = fragments;
}
/* (non-Javadoc)
 * @see android.support.v4.app.FragmentPagerAdapter#getItem(int)
 */
@Override
public Fragment getItem(int position) {
    return this.fragments.get(position);
}


@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    registeredFragments.remove(position);
    super.destroyItem(container, position, object);
}


public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

/* (non-Javadoc)
 * @see android.support.v4.view.PagerAdapter#getCount()
 */
@Override
public int getCount() {
    return this.fragments.size();
}

}

和我的 LogingFragment。其他 2 个片段完全相同：

public class LogingFragment extends Fragment{

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;
    }
    return (LinearLayout)inflater.inflate(R.layout.coach_activity, container, false);
}

}

每件事都完美无缺，所有查看和滑动都可以正常工作，但是在 setup() 方法中，我得到了 nullPointer。请帮帮我。

4

4 回答 4

1

我强烈建议运行和测试使用 Tabs 和 ViewPager 的示例 Effective Navigation

http://developer.android.com/training/implementing-navigation/index.html

于 2013-07-22T17:37:11.297 回答
1

最后我弄清楚了nullpointer的原因是什么。寻呼机适配器应该是这样的：

public class PagerAdapter extends FragmentPagerAdapter {

Fragment screens[];
public PagerAdapter(FragmentManager fm, MainActivity context) {
    super(fm);
    screens = new Fragment[3];
    screens[0] = Fragment.instantiate(context,CoachFragment.class.getName() );
    screens[1] = Fragment.instantiate(context,LogingFragment.class.getName() );
    screens[2] = Fragment.instantiate(context,HistoryFragment.class.getName() );
}

@Override
public Fragment getItem(int index) {
    if(index <= screens.length)
    {
        return screens[index];
    }
    return null;
}

@Override
public int getCount() {
    return screens.length;
}

}

因此实例化视图寻呼机更改如下：

private void intialiseViewPager() {


    this.mPagerAdapter = new PagerAdapter(super.getSupportFragmentManager(),this);
    //
    this.mViewPager = (ViewPager) super.findViewById(R.id.viewpager);
    this.mViewPager.setAdapter(this.mPagerAdapter);
    this.mViewPager.setOnPageChangeListener(this);
    //
    this.mViewPager = (ViewPager) super.findViewById(R.id.viewpager);
    this.mViewPager.setAdapter(this.mPagerAdapter);
    this.mViewPager.setOnPageChangeListener(this);
}

感谢@Bruno Mateus

于 2013-07-23T11:41:24.847 回答
0

在我看来，您似乎是 android 新手，所以让我为您指明正确的方向（如果您对 android 不陌生，我深表歉意）：

如果你想在你的应用中使用标签，最新最好的方法是使用Action Bar tabs。

这仅涉及编辑您的menu.xml文件onCreateOptionsMenu()并向您的主要活动添加方法。

另外，为了回答你的问题，

所以唯一剩下的是如何访问选项卡片段以从我的 FragmentActivity 调用方法

您不应该使用您的片段从您的片段活动中调用方法。

再次，我将通过这个视频“使用片段编程 Android”为您指明正确的方向。它有点长，但会解释如何使用片段。

使用视频的片段示例并将其与操作栏选项卡页面中的示例代码相结合。

祝你好运

**快速编辑澄清：您应该使用操作栏选项卡，因为这是使用选项卡的最新和最简单的方法。这是新的“最佳实践”。TabWidget 和 TabActivity 更老、更复杂，据我所知甚至可能被弃用。

于 2013-07-22T17:11:48.390 回答
0

试试GrilledUI库。它将为您完成所有繁琐的工作，甚至从 XML 加载选项卡列表。

于 2013-07-23T17:01:54.297 回答