实现简单的观点和片段标签 [英] implementing tabs with simple views and fragments

问题描述

在与实施标签像TabActivity和片段和viewPager的常用方法1周斗争我没能得到活动或制表符的片段的实例，并不能找到一个方法来解决这个问题。所以我决定来实现它以不同的方式。首先我做一个简单的按钮tabWidget。在Android开发者网站，我找到一个方式运行，以取代片段。所以唯一的事情仍然是如何获得访问标签片段调用从我FragmentActivity方法。

After one week struggle with common ways of implementing tabs like TabActivity and fragments and viewPager I failed to get a instance of Activities or fragments of tabs and couldn't find a way to solve the issue. So I decided to implement it in a different way. First I make a tabWidget with a simple button. In android developer website I find out a way to replace fragment in runtime. so the only thing remains is that how to get access to tab fragments to invoke methods from my FragmentActivity.

下面是一个使用pageViewer我FragmentActivity。我得到空指针，当我想找到自己的标签片段对象设置（）方法：

here is my FragmentActivity using pageViewer. I get nullpointer when I want to get fragment object of my tab in setup() method:

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pageAdapter：

my pageAdapter:

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LogingFragment。其他2片段是完全一样的之一：

and my LogingFragment. the other 2 fragments are exactly the same one:

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);
}

}

每一件事情完美的作品，所有的前瞻性和刷卡工作正常，但在设置（）方法中，我得到空指针。请大家帮帮我吧。

Every Thing works perfect and all looking and swiping works fine but in setup() method I get nullPointer. please help me with it.

推荐答案

最后我想通了什么是空指针的原因。寻呼机适配器应该是这样的：

Finally I figured it out what is the cause of nullpointer. pager adapter should be like this:

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;
}

}

所以实例化视图寻呼机变化象下面这样：

so instantiating view pager changes like below:

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);
}

由于@Bruno马特乌斯

Thanks to @Bruno Mateus

这篇关于实现简单的观点和片段标签的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！