Android网络问题

Question

你好，我的应用程序有一些问题:第一次:它工作并显示我的字符串从服务器第二次:它没有显示我的字符串从服务器第三次：“已停止”我有什么问题？

public class MenuActivity extends Activity {

    private static ArrayList<Products> myProducts;
    ParseJSON parseJSON;

    final String GetMenuUrl = "http://xn--e1aybc.xn--76-6kc1ag2ab9l.xn--p1ai/get_menu.php";
    String City = "Moscow";
    String NameCinema = "Avrora";
    private ProgressDialog dialog;
    private String response;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.menu);
        init();
        new RequestTask().execute(GetMenuUrl);
    }

public void init(){
    myProducts = new ArrayList<Products>();
    parseJSON = new ParseJSON();
}


private void setAdapter(ArrayList<String> products){
    ListView lv = (ListView)findViewById(R.id.listProducts);
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,   android.R.layout.simple_list_item_1, products);
    lv.setAdapter(adapter);
}

class RequestTask extends AsyncTask<String, String, String> {
    @Override
    protected String doInBackground(String... params) {
        try {
            DefaultHttpClient hc = new DefaultHttpClient();
            ResponseHandler<String> res = new BasicResponseHandler();

            HttpPost postMethod = new HttpPost(params[0]);
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
            nameValuePairs.add(new BasicNameValuePair("city", City));
            nameValuePairs.add(new BasicNameValuePair("name_cinema",NameCinema));
            postMethod.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            response = hc.execute(postMethod, res);

            parseJSON.parse(response.toString());
            Log.d("response == ", response.toString());
            myProducts = parseJSON.getObjects();

            Log.d("firstProduc == ", myProducts.get(0).getProductName());

            ArrayList<String> products = new ArrayList<String>();
            for(int i = 0 ; i < myProducts.size(); i++){
                products.add(myProducts.get(i).getProductName());
            }
            setAdapter(products);
        } catch (Exception e) {
            System.out.println("Exp=" + e);
        }
        return null;
    }
    @Override
    protected void onPostExecute(String result) {
        dialog.dismiss();
        super.onPostExecute(result);
    }
    @Override
    protected void onPreExecute() {
        dialog = new ProgressDialog(MenuActivity.this);
        dialog.setMessage("Loading...");
        dialog.setIndeterminate(true);
        dialog.setCancelable(true);
        dialog.show();
        super.onPreExecute();
    }
}

日志上说：

10-22 16:01:50.132    1604-1604/com.example.kinofood E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at android.widget.AbsListView$RecycleBin.getScrapView(AbsListView.java:6310)
            at android.widget.AbsListView.obtainView(AbsListView.java:2139)
            at android.widget.ListView.measureHeightOfChildren(ListView.java:1246)
            at android.widget.ListView.onMeasure(ListView.java:1158)
            at android.view.View.measure(View.java:15518)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:15518)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:15518)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:847)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:15518)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4825)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2176)
            at android.view.View.measure(View.java:15518)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1874)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1089)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1265)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:989)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4351)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
            at android.view.Choreographer.doCallbacks(Choreographer.java:562)
            at android.view.Choreographer.doFrame(Choreographer.java:532)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
            at android.os.Handler.handleCallback(Handler.java:725)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
10-22 16:01:50.156      476-487/system_process W/ActivityManager﹕ Force finishing activity com.example.kinofood/.MenuActivity

Answer 1

setAdapter(products);应该从UI Thread中调用，而不是在doInBackground()中调用，因为您在ListView上设置Adapter，这应该在UI Thread上完成。把电话转到onPostExecute()。

这意味着您希望将products传递给onPostExecute()，或者更好的做法是将其作为任务类的成员变量，然后可以将结果传递给onPostExecute()，以确保在尝试设置Adapter而不是返回null之前收到了数据。

class RequestTask extends AsyncTask<String, String, String> {
    //declare it here
    ArrayList<String> products = new ArrayList<String>();

    @Override
    protected void onPostExecute(String result) {
        // it's a good idea to check if your dialog isn't null and showing
        if (dialog != null && dialog.isShowing() 
            dialog.dismiss();

        // call the method here
        setAdapter(products);
        super.onPostExecute(result);
    }

而且，正如我所说的，您可能需要检查doInBackground()中的响应，或者products和return的大小--响应或大小--以确定您是否得到了任何信息。