android – 从Activity完成异步后填充Fragment上的ListView

我有一个主要活动,它将从url异步中获取 JSON数据

这是MainActivity.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener{
    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;
 
    //Tab titles
    private String[] tabs = {"Sermons","More"};
    private String[] sermonsList = new String[0];
 
    //JSON URL for sermonList data
    private static String sermonListJSONUrl = "https://dl.dropBoxusercontent.com/u/12345/index.PHP";
 
    //Variable to save JSON Object
    private static final String JSON_KEY_SERMONS = "sermon";
 
    private JSONObject sermonListJSONObject = null;
    private JSONArray sermonListJSONArray = null;
    SermonsFragment mSermonFragment;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        //Call JSONParser Asynchronously to get sermonList in JSON Format
 
        new callJSONParserAsync().execute(sermonListJSONUrl);
        //this.mSermonFragment = (SermonsFragment) getFragmentManager().findFragmentById(android.R.id.list);
        this.mSermonFragment = (SermonsFragment) getFragmentManager().findFragmentById(R.id.pager);
 
        //Initialization
        viewPager = (ViewPager) findViewById(R.id.pager);
        actionBar = getActionBar();
        mAdapter = new TabsPagerAdapter(getFragmentManager());
 
        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
 
        //Adding Tabs
        for(String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name).setTabListener(this));
        }
 
        /**
         * on swiping the viewpager make respective tab selected
         */
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position,float positionOffset,int positionOffsetPixels) {
 
            }
 
            @Override
            public void onPageSelected(int position) {
                //on changing the page
                //make respected tab selected
                actionBar.setSelectedNavigationItem(position);
            }
 
            @Override
            public void onPageScrollStateChanged(int state) {
 
            }
        });
    }

这是activity_main.xml

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</android.support.v4.view.ViewPager>

这是SermonsFragment.java

public class SermonsFragment extends ListFragment {
    private String[] sermonsList;
    ArrayAdapter listAdapter;
 
    String imageUrl = "https://fbcdn-sphotos-b-a.akamaihd.net/" +
            "hphotos-ak-prn2/t1.0-9/10415605_10132423542_6220704573655530117_n.jpg";
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
 
        sermonsList = ((MainActivity)getActivity()).getSermonsList();
 
        //ListView for the sermon list,only show if there is something in listview
        listAdapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,sermonsList);
 
        if(listAdapter.getCount() != 0) {
            setListAdapter(listAdapter);
        }
    }
 
    @Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_sermons,container,false);
 
        // show The Image
        new getSermonBannerImage((ImageView) rootView.findViewById(R.id.series_banner))
                .execute(imageUrl);
 
        return rootView;
    }
 
    public void updateListView(String[] newData) {
        if(newData.length == 0) {
            Log.d("myTesting3","sermonsList is Empty");
        } else {
            Log.d("myTestingSermonFragment",newData[0]);
            Log.d("myTestingSermonFragment",newData[1]);
        }
 
        sermonsList = newData;
        Log.d("myTestingSermonFragment",sermonsList[1]);
        this.listAdapter.clear();
        this.listAdapter.addAll(newData);
        this.listAdapter.notifyDataSetChanged();
    }

这是fragment_sermon.xml

<?xml version="1.0" encoding="utf-8"?>
 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="#222222" >
 
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
 
        <!-- Shows an image from your drawable resources -->
        <ImageView
            android:id="@+id/series_banner"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_gravity="center"
            android:src="@drawable/series_banner" />
        <!-- Closing tag for the horizontal nested layout -->
 
        <View
            android:layout_width="fill_parent"
            android:layout_height="10dp"
            android:layout_marginBottom="10dp"
            android:background="@android:color/darker_gray"/>
 
        <ListView
            android:id="@android:id/list"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:background="#ffffffff" />
 
        <TextView
            android:id="@android:id/empty"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:gravity="center"
            android:text="No Data" />
    </LinearLayout>
</RelativeLayout>

这是TabsPagerAdapter.java

public class TabsPagerAdapter extends FragmentPagerAdapter {
 
    public TabsPagerAdapter(FragmentManager fm) {
        super(fm);
    }
 
    @Override
    public Fragment getItem(int index) {
        switch (index) {
            case 0:
                //Sermons fragment activity
                return new SermonsFragment();
            case 1:
                //More fragment activity
                return new MoreFragment();
 
        }
 
        return null;
    }
 
    @Override
    public int getCount() {
        //get item count - equal to number of tabs
        return 2;
    }
}

最后这是错误

07-27 16:42:27.921    1549-1555/org.myapp.myapp E/jdwp﹕ Failed writing handshake bytes: Broken pipe (-1 of 14)
07-27 16:42:29.941    1549-1549/org.myapp.myapp E/OpenGLRenderer﹕ Getting MAX_TEXTURE_SIZE from GradienCache
07-27 16:42:29.941    1549-1549/org.myapp.myapp E/OpenGLRenderer﹕ MAX_TEXTURE_SIZE: 16384
07-27 16:42:29.953    1549-1549/org.myapp.myapp E/OpenGLRenderer﹕ Getting MAX_TEXTURE_SIZE from Caches::initConstraints()
07-27 16:42:29.953    1549-1549/org.myapp.myapp E/OpenGLRenderer﹕ MAX_TEXTURE_SIZE: 16384
07-27 16:42:30.353    1549-1549/org.myapp.myapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: org.myapp.myapp,PID: 1549
    java.lang.NullPointerException
            at org.myapp.myapp.MainActivity$callJSONParserAsync.onPostExecute(MainActivity.java:174)
            at org.myapp.myapp.MainActivity$callJSONParserAsync.onPostExecute(MainActivity.java:157)
            at android.os.AsyncTask.finish(AsyncTask.java:632)
            at android.os.AsyncTask.access$600(AsyncTask.java:177)
            at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

我不确定为什么会出现OpenGLRenderer错误,但是自从我创建这个应用程序以来它一直存在并运行得很好,所以这不是问题(尽管如果你能指出如何解决这个问题会很棒). MainActivity.java:174是mSermonFragment.updateListView(sermonsList)上的这一行;

我怎样才能确保它正确填充？最好是异步,因此它不会锁定UI,可能是在异步完成后更新listview.

如果你也可以指出,如果在异步期间如何制作它会很好,它将检查是否有互联网连接,列表视图将显示加载圈,如果它没有互联网,或者空列表它将显示否数据,否则会显示清单

解决方法

由于您只有两个片段,因此可以跟踪它们保存实例.使用回调建议它不是最好的选择.

所以,在你的寻呼机适配器中：

public class TabsPagerAdapter extends FragmentPagerAdapter {
 
    SermonsFragment mSermonsFragment;
    MoreFragment mMoreFragment;
 
    public TabsPagerAdapter(FragmentManager fm) {
        super(fm);
        this.mSermonsFragment = new SermonsFragment();
        this.mMoreFragment = new MoreFragment();
    }
 
    @Override
    public Fragment getItem(int index) {
        switch (index) {
            case 0:
                //Sermons fragment activity
                return mSermonsFragment;
            case 1:
                //More fragment activity
                return mMoreFragment;
 
        }
 
        return null;
    }
 
    @Override
    public int getCount() {
        //get item count - equal to number of tabs
        return 2;
    }
 
    public updateSermonsFragment(String[] data) {
         mSermonsFragment.updateData(data);
    }
 
    //i don't know what's the data type managed by MoreFragment
    public updateMoreFragment(Object data) {
         mMoreFragment.updateData(data)
    }
}

创建一个方法来更新片段中的适配器：

public void updateData(String[] newData) {
    this.listAdapter.clear();
    for(int i = 0; i < newData.length; i++) {
        this.listAdapter.add(newData[i]);
    }
    this.listAdapter.notifyDataSetChanged();
}

然后你可以从你的适配器方法的AsyncTask的onPostExecute中调用这个方法：

protected void onPostExecute(JSONObject jsonObject) {
    sermonListJSONObject = jsonObject;
    sermonListJSONArray = 
            parseJSONObjToJSONArray(sermonListJSONObject,JSON_KEY_SERMONS);
 
    String[] sermonsList;
 
    .... // here you need set an array with the strings you parsed
 
    //here you call the new method on the adapter to update your data.
    mAdapter.updateSermonsFragment(sermonsList);
 }

另一个最佳实践是在片段中定义静态newInstace(String []数据)方法,这样您就可以在第一次网络调用时初始化片段数据,以确保您的片段有一个数据集可以使用,然后如上所述进行更新.

android – 从Activity完成异步后填充Fragment上的ListView

解决方法

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