如何从JSON获取数据后在另一个片段活动中添加Imageview？

Question

我有一个使用TabHost运行的android应用程序。 我想在MainActivity中获取JSON数据后，在另一个片段活动中更新并添加图像视图。 但是，当我在MainActivity类中调用shp.AddImages（）时，应用程序崩溃了。 请帮帮忙~~

public class MainActivity extends FragmentActivity implements OnTabChangeListener, OnPageChangeListener {

    private TabsPagerAdapter mAdapter;

    private ViewPager mViewPager;

    private TabHost mTabHost;

    private String server_url = "http://comicking.blob.core.windows.net/xml/testing.json";

    private JSONHandler obj;

    private Handler mHandler = new Handler();

    ArrayList<Book> bookList;

    BookAdapter bookadapter;



    @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH) 
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        bookList = new ArrayList<Book>();

        mViewPager = (ViewPager) findViewById(R.id.viewpager);

        InitialiseTabHost();

        mAdapter = new TabsPagerAdapter(getSupportFragmentManager());             

        mViewPager.setAdapter(mAdapter);

        mViewPager.setOnPageChangeListener(MainActivity.this);

        new JSONAsyncTask().execute(server_url);

        bookadapter = new BookAdapter(getApplicationContext(), R.layout.row, bookList);

        Shop shop = new Shop();
        shop.AddImages(bookList);


    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
     // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle presses on the action bar items
        switch (item.getItemId()) {
            case R.id.Refresh:
                //openSearch();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
    // Method to add a TabHost
    private static void AddTab(MainActivity activity, TabHost tabHost, TabHost.TabSpec tabSpec) {

        tabSpec.setContent(new MyTabFactory(activity));

        tabHost.addTab(tabSpec);

    }
    // Manages the Tab changes, synchronizing it with Pages
    public void onTabChanged(String tag) {

        int pos = this.mTabHost.getCurrentTab();

        this.mViewPager.setCurrentItem(pos);

    }

    @Override
    public void onPageScrollStateChanged(int arg0) {

    }

    // Manages the Page changes, synchronizing it with Tabs

    @Override
    public void onPageScrolled(int arg0, float arg1, int arg2) {

        int pos = this.mViewPager.getCurrentItem();

        this.mTabHost.setCurrentTab(pos);

    }

    @Override
    public void onPageSelected(int arg0) {

    }

    private void InitialiseTabHost() {

        mTabHost = (TabHost) findViewById(android.R.id.tabhost);

        mTabHost.setup();

        MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Home").setIndicator("Home"));

        MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Shop").setIndicator("Shop"));

        MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Collection").setIndicator("Collection"));

        MainActivity.AddTab(this, this.mTabHost, this.mTabHost.newTabSpec("Help").setIndicator("Help"));

        mTabHost.setOnTabChangedListener(this);

    }

Asynctask类

class JSONAsyncTask extends AsyncTask<String, Void, Boolean> {

        ProgressDialog dialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            dialog = new ProgressDialog(MainActivity.this);
            dialog.setMessage("Loading, please wait");
            dialog.setTitle("Connecting server");
            dialog.show();
            dialog.setCancelable(false);
        }

        @Override
        protected Boolean doInBackground(String... urls) {
            try {

                //------------------>>
                HttpGet httppost = new HttpGet(urls[0]);
                HttpClient httpclient = new DefaultHttpClient();
                HttpResponse response = httpclient.execute(httppost);

                // StatusLine stat = response.getStatusLine();
                int status = response.getStatusLine().getStatusCode();

                if (status == 200) {
                    HttpEntity entity = response.getEntity();
                    String data = EntityUtils.toString(entity);


                    JSONObject jsono = new JSONObject(data);
                    JSONArray jarray = jsono.getJSONArray("book");

                    for (int i = 0; i < jarray.length(); i++) {
                        JSONObject object = jarray.getJSONObject(i);

                        Book book = new Book();

                        book.setName(object.getString("name"));
                        book.setImage(object.getString("img"));

                        bookList.add(book);
                    }

                    return true;
                }

                //------------------>>

            } catch (ParseException e1) {
                e1.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            }
            return false;
        }

        protected void onPostExecute(Boolean result) {
            dialog.cancel();
            //bookadapter.notifyDataSetChanged();
            if(result == false)
                Toast.makeText(getApplicationContext(), "Unable to fetch data from server", Toast.LENGTH_LONG).show();

        }
    }


}

片段类

public class Shop extends Fragment {

    public Map<String,Book> shoplist = new HashMap<String,Book>();
    private View rootView;
    private LinearLayout shopLL;
    private Context c;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        rootView = inflater.inflate(R.layout.shop, container, false);
        shopLL = (LinearLayout) rootView.findViewById(R.id.shopLinearLayout);

        return rootView;
    }

    public void AddImages(ArrayList<Book> booklist){

        c = getActivity().getApplicationContext();

        for(int i = 0; i < booklist.size(); i++){

            ImageView img= new ImageView(c);
            shopLL.addView(img);

        }

    }

}

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<TabHost
android:id="@android:id/tabhost"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:android="http://schemas.android.com/apk/res/android">

<RelativeLayout
    android:layout_width="match_parent"
    android:id="@+id/linearLayout1"
    android:layout_height="match_parent">

    <TabWidget
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@android:id/tabs"
        android:layout_alignParentBottom="true">
    </TabWidget>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@android:id/tabcontent">
    </FrameLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_above="@android:id/tabs"
        android:layout_gravity="bottom" />

</RelativeLayout>
</TabHost>

Shop.xml

<RelativeLayout       xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<HorizontalScrollView
    android:id="@+id/horizontalScrollView1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true" >

    <LinearLayout
         android:id="@+id/shopLinearLayout"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:orientation="horizontal" >

            <ImageView
                android:id="@+id/item1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                 android:src="@drawable/ic_launcher" />

    </LinearLayout>

</HorizontalScrollView>


</RelativeLayout>

Answer 1

你可以发布你的布局xml吗？ 假设您在布局文件中定义了“ Shop”片段，则可以通过id获得对该片段的引用。 然后，您可以使用返回的列表调用Shop片段类上的方法。

Answer 2

Asynctask是您使用的后端服务，您可能会返回一个对象而不是布尔值

修改JSONAsyncTask：-

//**** e.g.
class JSONAsyncTask extends AsyncTask<String, Void, JSONObject> {
    // define a caller
    Shop caller;

    //create a Constructor for caller;
    public JSONAsyncTask (Shop caller) {
        // TODO Auto-generated constructor stub
         this.caller = caller;
    }

    ///&& method doInBackground
    @Override
    protected JSONObject doInBackground(String... urls) {
          .....


         //custom your returning jsonObject 
         return jsonobject;
    }

    ////&& return jsonobject back to ur fragment class here by pass in caller
    protected void onPostExecute(JSONObject jsonObject) {
        caller.onBackgroundTaskCompleted(jsonObject);
    }

}

在将MainActivity类方法转换为Shopfragment类时，获取ur json对象：

    @Override
    public void onResume() {
           new JSONAsyncTask().execute(server_url);
    }


//your returning result
public void onBackgroundTaskCompleted(JSONObject result) {
        Log.i("TAG", result:"+result);

        if(result!=null){
            //process your result to get the booklist here

            Booklist booklist;


           addimage(booklist);


         }

}

Gd运气:)