Android 应用仅在第二次运行后才显示列表视图

Question

我的应用程序应该从网站（JSON 格式）获取一些信息，对其进行解析，将其存储在 SQLite 数据库中，然后在列表视图中显示项目列表（从数据库中获取）。除了填充列表视图之外，它执行所有操作（使用 Log.v 消息检查）。但是如果我第二次运行它，就会显示列表视图。

在 MainActivity 中，我使用 AsyncTask 来获取解析后的数据。然后我启动另一个活动来从表中读取数据（所有行）并将它们显示在 ListView 中。

public class MainActivity extends Activity {
private MySQLiteHelper dbHelper; 
private SQLiteDatabase db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    String url = "http://strong-earth-32.heroku.com/stores.aspx";

    dbHelper = new MySQLiteHelper(this); 
    db = dbHelper.getWritableDatabase();

    ConnectAsyncTask connect = new ConnectAsyncTask(url);
    connect.execute();
    try {
        connect.wait(2000);
    } catch (Exception e) {
        Log.v("Waiting. ",e.getStackTrace().toString());
    }
    Intent intent=new Intent(MainActivity.this,DisplayActivity.class);
    startActivity(intent);

}

@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;
}

public void cacheData(String result) {
    ContentValues cv = new ContentValues();
    try {
        //Tranform the string into a json object
       final JSONObject json = new JSONObject(result);
       JSONArray jArray = json.getJSONArray("stores");
        for(int i = 0; i < jArray.length(); i++) {
            try{
                JSONObject oneObject = jArray.getJSONObject(i);
                String logoURL = oneObject.getString("storeLogoURL");
                String address = oneObject.getString("address");
                cv.put(MySQLiteHelper.COLUMN_ADDRESS, address);
                String phoneNr = oneObject.getString("phone");
                cv.put(MySQLiteHelper.COLUMN_PHONE, phoneNr);
                long row = db.insert(MySQLiteHelper.TABLE_STORES, MySQLiteHelper.COLUMN_ID, cv);
                //Log.v("row= ", row + "");
                cv.clear();
            } catch (JSONException e) {
                Log.v("Oops! ",e.getStackTrace().toString());
            }
        }
    } catch (JSONException e) {
        Log.v("ERR",e.getStackTrace().toString());
    }
}   



private class ConnectAsyncTask extends AsyncTask<Void, Void, String>{
        private ProgressDialog progressDialog;
        String url;
        ConnectAsyncTask(String urlPass){
            url = urlPass;
        }
        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            progressDialog = new ProgressDialog(MainActivity.this);
            progressDialog.setMessage("Fetching data, Please wait...");
            progressDialog.setIndeterminate(true);
            progressDialog.show();
        }
        @Override
        protected String doInBackground(Void... params) {
            JSONparser jParser = new JSONparser();
            String json = jParser.getJSONFromUrl(url);
            return json;
        }
        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);   
            progressDialog.hide();
            progressDialog.dismiss();
            if (result!=null) {
                Log.v("READY","READY");
                cacheData(result);
            }
        }
    }

}

这是另一个活动：

public class DisplayActivity extends Activity {
private MySQLiteHelper dbHelper; 
private SQLiteDatabase db;
private ListView lv_custom;
ArrayList<Content> contents = new ArrayList<Content>();
Content content0 = new Content();
Cursor c;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_display);
    lv_custom = (ListView) findViewById(android.R.id.list);

    dbHelper = new MySQLiteHelper(this); 
    db = dbHelper.getWritableDatabase();
    readData(db);
    lv_custom.setAdapter(new CustomListviewAdapter(this, R.layout.one_row, contents));

}

private class Content {
    private String logoURL;
    private String phoneNr;
    private String address;
}

private class ViewHolder{
    WebView webView;
    TextView textViewPhone;
    TextView textViewAddress;
}


private class CustomListviewAdapter extends BaseAdapter{

    private int layoutResource;
    private ArrayList<Content> mArrayList;
    private LayoutInflater inflater;


    public CustomListviewAdapter(Context mContext, int layoutResource, ArrayList<Content> mArrayList) {
        this.layoutResource = layoutResource;
        this.mArrayList = mArrayList;
        inflater = LayoutInflater.from(mContext);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return mArrayList.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return mArrayList.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;

            convertView = inflater.inflate(layoutResource, null);
            viewHolder = new ViewHolder();

            //WebView web = (WebView) findViewById(R.id.webView1);
            //web.loadUrl("Your Url");
            //viewHolder.webView = (WebView) findViewById(R.id.webView1);
            viewHolder.textViewPhone = (TextView) convertView.findViewById(R.id.phoneNr);
            viewHolder.textViewAddress = (TextView) convertView.findViewById(R.id.address);

        //viewHolder.webView.loadUrl(mArrayList.get(position).logoURL);
        viewHolder.textViewPhone.setText(mArrayList.get(position).phoneNr);
        viewHolder.textViewAddress.setText(mArrayList.get(position).address);

        //int itemHeight = height/4 - 10;

        //viewHolder.webView.setLayoutParams(new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, itemHeight));

        return convertView;
    }

}

public void readData(SQLiteDatabase db) {
String[] selectionArguments = {};
c = db.rawQuery("SELECT * FROM storesList", selectionArguments);
if (c.getCount() != 0) {
try {
    while (c.moveToNext()) {
        //add a new store information to the ArrayList
        content0 = new Content();
        //content0.logoURL = logoURL;
        content0.phoneNr = c.getString(2);
        content0.address = c.getString(1);
        contents.add(content0);
        Log.v("address:", content0.address);
    } 
} catch (Exception e) {
    Log.v("Exception e ",e.fillInStackTrace().toString());
}}
else Log.v("Cursor ", 0+"");
}

}

为什么我看不到应用程序第一次执行时的列表？我想这与在 AsyncTask 完成之前开始的第二个活动有关。但是，我没有解决问题的方法。此外，我没有看到 ProgressDialog。任何想法？

Answer 1

尝试在 MainActivity.java 的 onPostExecute 中调用启动第二个活动。

从 MainActivity.java 的 onCreate() 中删除以下代码

Intent intent=new Intent(MainActivity.this,DisplayActivity.class);
    startActivity(intent);

并替换onPostExecute，如下所示

@Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);   
            progressDialog.hide();
            progressDialog.dismiss();
            if (result!=null) {
                Log.v("READY","READY");
                cacheData(result);
                 Intent intent=new Intent(MainActivity.this,DisplayActivity.class);
        startActivity(intent);
            }
        }

Answer 2

为什么我看不到应用第一次执行时的列表？

因为您在调用AsyncTask 的execute 方法之后正在启动另一个活动。要在第二个活动中显示数据，您需要在 cacheData 方法内的 db 中插入数据后启动第二个活动：

public void cacheData(String result) {
     //your code for inserting data in db
     ....

    //start second Activity here
    Intent intent=new Intent(MainActivity.this,DisplayActivity.class);
    startActivity(intent);
}