Question

我正在试图弄清楚在运行UI和设置ViewPager适配器之前如何从服务器下载内容。我的服务器上有JSON文件，应用程序正确读取，但我无法更新ViewPager。

理想情况下，我想做的是制作一个对话框，上面写着“请等待，我们正在检查是否有任何新内容”，带有循环加载的东西（只是为了表明它正在工作），如果是的话 - 来下载它并使内容新鲜，如果不使用最后的内容。

现在看来就是这样。它按原样工作 - 我应该从哪里拿到它？

public class MainActivity extends Activity {

MediaPlayer mp;
ViewPager viewPager;
PagerAdapter adapter;
//int[] sounds;
int[] g;
String[] title;
int[] description;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.viewpager_main);

    // Generate data

    title = new String[] { "A1", "A2", "A3","A4" };

    description = new int[] { R.string.a1, R.string.a2, R.string.a3, R.string.a4 };

    gun = new int[] {R.drawable.obr4,R.drawable.obr4,R.drawable.obr4,R.drawable.obr4};

    // Locate the ViewPager in viewpager_main.xml
    viewPager = (ViewPager) findViewById(R.id.pager);
    // Pass results to ViewPagerAdapter Class
    adapter = new ViewPagerAdapter(MainActivity.this, g, title,
            description);
    // Binds the Adapter to the ViewPager
    viewPager.setAdapter(adapter);

    if (VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        viewPager.setPageTransformer(true, new DepthPageTransformer());
    }



    new GetUpdate().execute();
}

class GetUpdate extends AsyncTask<Void, Void, Void>{

    JSONObject jobj = null;
    @Override
    protected Void doInBackground(Void... params) {             

        //JSON
        JSONParser jparser = new JSONParser();
        JSONObject data = jparser.getJSONFromUrl("http://myserver.com/file.json");                      

        String title2 = "";

        try {
            jobj = data.getJSONObject("party2");                
            title2 = jobj.getString("title");
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        //title = new String[] { title2,title2,title2,title2}; <- commented 'cause doesn't work

        return null;
    }

}

Answer 1

获取新的JSON之后，只需更新适配器的源列表，并在适配器对象上执行'notifyDataSetChanged（）`，如下所示。

public class MainActivity extends Activity {

MediaPlayer mp;
ViewPager viewPager;
PagerAdapter adapter;
//int[] sounds;
int[] g;
String[] title;
int[] description;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.viewpager_main);

    // Generate data

    title = new String[] { "A1", "A2", "A3","A4" };

    description = new int[] { R.string.a1, R.string.a2, R.string.a3, R.string.a4 };

    gun = new int[] {R.drawable.obr4,R.drawable.obr4,R.drawable.obr4,R.drawable.obr4};

    // Locate the ViewPager in viewpager_main.xml
    viewPager = (ViewPager) findViewById(R.id.pager);
    // Pass results to ViewPagerAdapter Class
    adapter = new ViewPagerAdapter(MainActivity.this, g, title,
            description);
    // Binds the Adapter to the ViewPager
    viewPager.setAdapter(adapter);

    if (VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        viewPager.setPageTransformer(true, new DepthPageTransformer());
    }



    new GetUpdate().execute();
}

class GetUpdate extends AsyncTask<Void, Void, Void>{

    JSONObject jobj = null;
    @Override
    protected Void doInBackground(Void... params) {             

        //JSON
        JSONParser jparser = new JSONParser();
        JSONObject data = jparser.getJSONFromUrl("http://myserver.com/file.json");                      

        String title2 = "";

        try {
            jobj = data.getJSONObject("party2");                
            title2 = jobj.getString("title");
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        // Change titles to ArrayList for better usage.
        title[4] = title2;
        adapter.notifyDataSetChanged();

        return null;
    }

}

Answer 2

您可以覆盖AsyncTask的onPostExecute（）方法，将更新逻辑放在那里

在UI显示之前加载内容（使用AsyncTask和ViewPager）

2 个答案: