Question

首先，我是一名机器人新手我正在创建一个简单的应用程序，它通过PHP脚本从服务器中提取一些数据，并在下一个Activity中的ListView中显示它们。但是，我发现如果脚本没有返回任何内容，则应用程序崩溃。所以我保持检查，只有当脚本返回一些数据时，应用程序才会切换到下一个活动。
这是我的代码。

public class HomeScreen extends ActionBarActivity {

String message3;
String message_short;
String[] items;
String[] short_items;
int check = 0;

private ProgressDialog dialog;

public String readJSONFeed(String URL)
{
    StringBuilder sb = new StringBuilder();
    HttpClient client = new DefaultHttpClient();
    HttpGet hg = new HttpGet(URL);
    try
    {
        HttpResponse response = client.execute(hg);
        StatusLine statusLine = response.getStatusLine();
        int statusCode = statusLine.getStatusCode();
        if(statusCode == 200)
        {
            HttpEntity en = response.getEntity();
            InputStream content = en.getContent();
            BufferedReader reader = new BufferedReader(new InputStreamReader(content));
            String line;
            while((line = reader.readLine()) != null)
            {
                sb.append(line);
            }
        }
        else
        {
            Log.e("JSON", "Failed to download File");
        }
    }
    catch(ClientProtocolException e)
    {
        e.printStackTrace();
    }
    catch(IOException e)
    {
        e.printStackTrace();
    }
    return sb.toString();
}

private class ReadJSONFeedTask extends AsyncTask<String, Void, String>
{
    protected void onPreExecute()
    {
        super.onPreExecute();
        dialog = new ProgressDialog(HomeScreen.this);
        dialog.setMessage("Downloading Notifications. Please wait . . .");
        dialog.setIndeterminate(false);
        dialog.setCancelable(false);
        dialog.show();
    }
    protected String doInBackground(String...urls)
    {
        return readJSONFeed(urls[0]);
    }
    protected void onPostExecute(String result)
    {
        dialog.dismiss();
        try
        {
            JSONArray jsonArray = new JSONArray(result);
            items = new String[jsonArray.length()];
            short_items = new String[jsonArray.length()];
            for(int i = 0; i < jsonArray.length(); i++)
            {
                JSONObject jobj = jsonArray.getJSONObject(i);
                message3 = "SUBJECT : " + jobj.getString("subject") + "\n\n" + 
                        "DATE : " + jobj.getString("date") + "\n" + jobj.getString("time") + "\n\n"
                         + "NOTICE : " + jobj.getString("notice");
                message_short = "SUBJECT : " + jobj.getString("subject") + "\n" 
                        + "NOTICE : " + jobj.getString("notice").substring(0, 20) + "..."
                        + "\n" + jobj.getString("time");
                items[i] = message3;
                short_items[i] = message_short;

                check += 1;
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

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

public void notificationPane(View view)
{

    String localhost = "http://10.0.2.2/example/json/notification.php";
    new ReadJSONFeedTask().execute(localhost);

    if(check != 0)
    {
        Intent i = new Intent(HomeScreen.this, NotificationPanel.class);
        i.putExtra("items", items);
        i.putExtra("short_items", short_items);
        startActivity(i);
    }
    else
    {
        Toast.makeText(getBaseContext(), "Either there is no notification to display or there might be a problem with your internet connection.", Toast.LENGTH_SHORT).show();
    }
}

public void recentNotice(View view)
{

    String localhost = "http://10.0.2.2/example/json/recent_notification.php";
    new ReadJSONFeedTask().execute(localhost);

    if(check != 0)
    {
        Intent i = new Intent(HomeScreen.this, NotificationPanel.class);
        i.putExtra("items", items);
        i.putExtra("short_items", short_items);
        startActivity(i);
    }
    else
    {
        Toast.makeText(getBaseContext(), "Either there is no notification to display or there might be a problem with your internet connection.", Toast.LENGTH_SHORT).show();
    }
}
}

int check是我检查服务器是否返回任何JSON数据的地方。如果check不为0，则不会切换到下一个activity。
但此代码的问题是，当我点击按钮时，它会显示TOAST {{1}甚至在它从服务器中提取数据之前，它就永远不会进入下一个活动Either there is no notification to display or there might be a problem with your internet connection.。我理解这是由于NotificationPanel.class。更奇怪的是，如果我多次单击该按钮，应用程序会突然切换到显示AsyncTask中数据的下一个活动。但它并不总是奏效。是否有解决这个问题的方法？
请帮忙。
提前谢谢你。

Answer 1

使用if else将代码移动到onPostExecute中的最后一个。检查结果时，AsyncTask仍处于执行状态。

Answer 2

您应该将这段代码放在onPostExecute方法中：

if(check != 0)
{
    Intent i = new Intent(HomeScreen.this, NotificationPanel.class);
    i.putExtra("items", items);
    i.putExtra("short_items", short_items);
    startActivity(i);
}
else
{
    Toast.makeText(getBaseContext(), "Either there is no notification to display or there might be a problem with your internet connection.", Toast.LENGTH_SHORT).show();
}

将它们放在当前代码之后，告诉我它是否有效。

＆＃34;更奇怪的是，如果我多次单击该按钮，应用程序会突然切换到下一个显示ListView中数据的活动。但它并不总是奏效。是否有解决这个问题的方法？＆＃34;

你在这里说的很清楚。一开始你不能运行你的意图，因为当你先点击几次按钮时，json还没有被提取。但是如果你继续点击它，它最终将获取JSON并能够进入下一个活动。

所以，我确定我所说的是需要做的事情。

修改我确定你的异步任务应该是这样的：

private class ReadJSONFeedTask extends AsyncTask<Void, Void, Void> { @Override protected void onPreExecute() { super.onPreExecute(); dialog = new ProgressDialog(HomeScreen.this); dialog.setMessage("Downloading Notifications. Please wait . . ."); dialog.setIndeterminate(false); dialog.setCancelable(false); dialog.show(); } //no need a return statment @Override protected Void doInBackground(Void... params) { try { JSONArray jsonArray = new JSONArray(readJSONFeed(urls[0])); items = new String[jsonArray.length()]; short_items = new String[jsonArray.length()]; for(int i = 0; i < jsonArray.length(); i++) { JSONObject jobj = jsonArray.getJSONObject(i); message3 = "SUBJECT : " + jobj.getString("subject") + "\n\n" + "DATE : " + jobj.getString("date") + "\n" + jobj.getString("time") + "\n\n" + "NOTICE : " + jobj.getString("notice"); message_short = "SUBJECT : " + jobj.getString("subject") + "\n" + "NOTICE : " + jobj.getString("notice").substring(0, 20) + "..." + "\n" + jobj.getString("time"); items[i] = message3; short_items[i] = message_short; check += 1; } } catch(Exception e) { e.printStackTrace(); } } @Override protected void onPostExecute(String result) { if(check != 0) { Intent i = new Intent(HomeScreen.this, NotificationPanel.class); i.putExtra("items", items); i.putExtra("short_items", short_items); startActivity(i); } else { Toast.makeText(getBaseContext(), "Either there is no notification to display or there might be a problem with your internet connection.", Toast.LENGTH_SHORT).show(); } dialog.dismiss(); } }

Android - 在通过AsyncTask提取JSON数据后，无法将数据发送到下一个活动（扩展ListActivity）

2 个答案: