Question

我正在尝试使用Asynctask从jdbc驱动程序加载数据并将此数据放在multimap中，然后将其加载到listview中

我目前有mainactivity.java，带有一个按钮和clicklistener（mainactivity上的这个按钮用于启动下一个活动）。

第二个活动已经启动了一个按钮，并且还有一个listview，其中填充了来自backgroundpickingtask.java的数据。 secondactivity.java实际上是我称之为“new BackgrounPickingTask.execute（）;

我遇到的问题是secondactivity.java中的按钮首先显示，但listview在secondactivity.java中显示之前需要一两秒钟。

我认为最好是从mainactivity准备好数据，这样第二个活动按钮（R.id.nextButton）在启动第二个活动时并不总是超出listview。对不起，如果我不清楚，但我尽力解释它。真的很感激任何帮助或建议。我是Android应用程序开发的新手。以下是课程。

MainActivity.class

public class MainActivity extends ActionBarActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button pickButton = (Button) findViewById(R.id.pickButton);

    View.OnClickListener pickListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, SecondActivity.class);
            MainActivity.this.startActivity(intent);
        }
    };
    pickButton.setOnClickListener(pickListener);

}

BackGroundPickingTask.java

public class BackgroundPickingTask extends AsyncTask<String, String, String> {


private Connection conn;
private String HOST = "jdbc:postgresql://IPaddress:(port number)/";
private String DataBaseNAME = "database";
private String USERNAME = "the_username";
private String PASSWORD = "the_password";
private PreparedStatement pStmt = null;
private ResultSet rs = null;
private long rowCounter = 0;
Multimap<String, String> myMultimap = ArrayListMultimap.create();

private String sql =
        "SELECT id, name, title, project from thattable"

ArrayAdapter<String> adapter;

@Override
protected void onPreExecute() {
    adapter = (ArrayAdapter<String>) (SecondActivity.list.getAdapter());
}

@Override
protected String doInBackground(String... params) {
    try {
        Class.forName("org.postgresql.Driver");
        conn = DriverManager.getConnection(
                HOST + DataBaseNAME, USERNAME, PASSWORD);

        //Prepares statement to execute query
        pStmt = conn.prepareStatement(sql);
        //Execute prepared statement
        rs = pStmt.executeQuery();
        //add results from sql query to multimap
        while (rs.next()) {
            myMultimap.put(rs.getString(1),rs.getString(2) + " (" + rs.getString(3) + " - " + rs.getString(4) + ")");
            ++rowCounter;
        }
        if (rowCounter == 0) {
            //System.out.println("There are no results");
        }
        rs.close();
        pStmt.close();

    } catch(Exception e) {
        e.printStackTrace();
    }
    //for loop to add values from each key to adapter
    for (String keyz : myMultimap.keySet()) {
        publishProgress(keyz);
    }
    return null;
}

@Override
protected void onProgressUpdate(String... values) {
    //formatting my string here to organize in listview
    String formattedString = "\nName (title- project):\n " + myMultimap.get(values[0]).toString()
            .replace("," , "\n").trim()
            .replace("[","").trim()
            .replace("]","").trim();
    //adding results to listview adapter
    adapter.add("ID: "  + values[0] + formattedString);
}


@Override
protected void onPostExecute(String values) {
}

SecondActivity.class

public class SecondActivity extends Activity {
public static ListView list;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_second);
    Button createWave = (Button) findViewById(R.id.nextButton);
    list = (ListView) findViewById(R.id.list);
    list.setAdapter(new ArrayAdapter<String>(this,
            R.layout.simple_list_item_1, new
            ArrayList<String>()));

    new BackgroundPickingTask().execute();            

}

Answer 1

使用ArrayAdapter作为参数的方法创建一个接口..

在SecondActivity上实现它..

使用arrayAdapter作为参数调用您在BackGroundPickingTask的onPostExecute中创建的Interface方法。

在SecondActivity上的实现方法中填充listView ..

那就是

Answer 2

public interface TaskInterface{
   void onLoadingCompleted();
}

<强> SecondActivity.java 默认情况下，您visibility中的invisible到xml。用

替换AysncTask调用

new BackgroundPickingTask(new TaskInterface(){
    @Override
    public void onLoadingCompleted(){
        yourButton.setVisibility(View.VISIBLE);
    }
 }
)).execute();

在AsyncTask中添加参数化构造函数

public class BackgroundPickingTask extends AsyncTask<String, String, String> {
private TaskInterface taskInterface;
public BackgroundPickingTask(TaskInterface task) {
        super();
        taskInterface = task 
    }

从按钮单击调用AsyncTask并在doInBackground完成后启动用listview填充的另一个活动

2 个答案: