android - 如何在应用程序开始时获得旋转进度条

Question

我是安卓新手。我设法将 JSON 文件解析到我的应用程序。现在我想使用 AsyncTask 获取 Spinning progressBa 直到应用程序启动并加载数据。我试图阅读很多东西，但它们只给出了如何在 onclick 事件或下载事件上获取进度条。

这是我的代码...

我只是对如何在启动应用程序时启动进度条以及以下代码的哪一部分转到 asycTask 类的哪个方法感到困惑....

package com.demojson;

import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;
import android.app.ListActivity;


public class MainActivity extends ListActivity {

    private static String url = "http://timepasssms.com/webservices/ws.php?type=category";

    private static final String TAG_DATA = "DATA";

    private static final String TAG_0 = "0";
    private static final String TAG_ID = "id";
    private static final String TAG_1 = "1";
    private static final String TAG_NAME = "name";
    private static final String TAG_2 = "2";
    private static final String TAG_DESCRIPTION = "description";
    private static final String TAG_3 = "3";
    private static final String TAG_NEW_NAME = "new_name";
    private static final String TAG_4 = "4";
    private static final String TAG_STATUS = "status";

    JSONArray jArray = null;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        ArrayList<HashMap<String, String>> contents = new ArrayList<HashMap<String, String>>();

        JSONMethod metObj = new JSONMethod();
        JSONObject jOb = metObj.getUrl(url);
        try {
            jArray = jOb.getJSONArray(TAG_DATA);

            for (int i = 0; i < jArray.length(); i++) {
                JSONObject child = jArray.getJSONObject(i);

                String tag_0 = child.getString(TAG_0);
                String id = child.getString(TAG_ID);
                String tag_1 = child.getString(TAG_1);
                String name = child.getString(TAG_NAME);
                String tag_2 = child.getString(TAG_2);
                String description = child.getString(TAG_DESCRIPTION);
                String tag_3 = child.getString(TAG_3);
                String new_name = child.getString(TAG_NEW_NAME);
                String tag_4 = child.getString(TAG_4);
                String status = child.getString(TAG_STATUS);

                HashMap<String, String> map = new HashMap<String, String>();
                map.put(TAG_NAME , name);

                contents.add(map);
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }

        ListAdapter adapter = new SimpleAdapter(this, contents,
                R.layout.list_items, new String[] { TAG_NAME },
                new int[] { R.id.tvName });
        setListAdapter(adapter);

        // --To get listview set...-- 

        ListView lv = getListView();
        lv.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                String item = ((TextView)view.findViewById(R.id.tvName)).getText().toString();
                Toast toast = Toast.makeText(getApplicationContext(), item , Toast.LENGTH_SHORT);
                toast.setGravity(Gravity.CENTER, 0, 0);
                toast.show();
            }
        }); 
    }


}

和 JSONMethod 类...

package com.demojson;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONObject;

import android.util.Log;

public class JSONMethod {
    InputStream is = null;
    JSONObject jObj=null;
    String json = "";



    public JSONObject getUrl(String url){
        try{
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            HttpResponse httpRespone = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpRespone.getEntity();
            is = httpEntity.getContent();

        }catch(UnsupportedEncodingException ue){

        }catch(ClientProtocolException ce){ 

        }catch(IOException ie){

        }

        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            StringBuilder sb = new StringBuilder();
            String line=null;
            while((line=br.readLine())!= null){
                sb.append(line + "/n"); 
            }
            is.close();
            json = sb.toString();

        }catch(Exception e){
            Log.e("JSONMethod", "Error converting result" + e.toString());
        }
        try{
            jObj = new JSONObject(json);
        }catch(Exception e){
            Log.e("JSONMethod", "Error parsing data" + e.toString());
        }

        return jObj;
    }
}

这里是xml文件...activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
    <!-- Main ListView 
         Always give id value as list(@android:id/list)
    -->

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="fill_parent"
        android:layout_height="60dp"
        android:src="@drawable/timepasssms" />

    <ListView
        android:id="@android:id/list"
        android:layout_width="fill_parent"
        android:layout_gravity="center"
        android:layout_height="wrap_content"/>

</LinearLayout>

和list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/round_edge"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/tvName"
        android:layout_width="fill_parent"
        android:layout_height="45dp"
        android:layout_marginLeft="10dp"
        android:gravity="left"
        android:padding="5dp"
        android:textColor="#DF7401"
        android:textSize="20dp" />

</LinearLayout>

Answer 1

这里是例子`

@Override
    protected void onPostExecute(Object table) {
        // TODO Auto-generated method stub
        super.onPostExecute(table);
        dialog.dismiss();
    }

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        dialog=ProgressDialog.show(Yourclass.this, "Loading Data.", "Please Wait");
    }

`希望对您有所帮助