从线程加载活动[关闭]

Question

您好，我有 2 项活动，一项称为登录，另一项称为 select_company 登录工作正常，但我似乎无法让它改变活动 使用以下代码调用这个类：

Login myActivity = new Login();
Login.Check_Login asyncTask = myActivity.new Check_Login();
asyncTask.execute();

我的班级：

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

        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        /**
         * getting All products from url
         * */
        protected String doInBackground(String... args) {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("username", Username));
            params.add(new BasicNameValuePair("password", Password));
            // getting JSON string from URL
            JSONObject json = jParser.makeHttpRequest("http://mobirep.co.za/server_scripts/check_login/check_login.php", "GET", params);

            // Check your log cat for JSON reponse
            Log.d("Status: ", json.toString());

            try {
                // Checking for SUCCESS TAG
                int success = json.getInt("success");
                TAG_SUCCESS = json.getString("success");
                if (success == 1) {
                    JSONArray login_details_onj = json.getJSONArray("login");
                    JSONObject login_details = login_details_onj.getJSONObject(0);
                    // Get The Data
                    Name = login_details.getString(TAG_NAME);
                    ID = login_details.getString(TAG_ID);
                    Company_ID = login_details.getString(TAG_COMPANY);
                }
                else 
                {
                    TAG_NAME = json.getString("success");
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            // dismiss the dialog after getting all products
            //pDialog.dismiss();
            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {
                    pDialog.dismiss();
                    Intent Select_company = new Intent(Login.this, Select_Company.class);
                    startActivity(Select_company);
                }
            });
        }
    }

doinbackground 一旦完成，它就会给我错误。 当成功 = 1 时，线程必须停止，发送数据并加载 select_company 活动 这是我的 LogCat：

05-14 13:39:51.863: E/Trace(4070): error opening trace file: No such file or directory (2)
05-14 13:39:53.273: D/dalvikvm(4070): GC_FOR_ALLOC freed 70K, 7% free 2598K/2792K, paused 154ms, total 161ms
05-14 13:39:53.422: I/dalvikvm-heap(4070): Grow heap (frag case) to 7.192MB for 4760016-byte allocation
05-14 13:39:53.752: D/dalvikvm(4070): GC_FOR_ALLOC freed 3K, 3% free 7243K/7444K, paused 228ms, total 228ms
05-14 13:39:54.082: D/dalvikvm(4070): GC_CONCURRENT freed <1K, 3% free 7251K/7444K, paused 10ms+53ms, total 291ms
05-14 13:39:55.083: I/Choreographer(4070): Skipped 42 frames!  The application may be doing too much work on its main thread.
05-14 13:39:55.452: D/gralloc_goldfish(4070): Emulator without GPU emulation detected.
05-14 13:39:56.082: I/Choreographer(4070): Skipped 33 frames!  The application may be doing too much work on its main thread.
05-14 13:40:04.203: I/Choreographer(4070): Skipped 65 frames!  The application may be doing too much work on its main thread.
05-14 13:40:04.443: I/Choreographer(4070): Skipped 32 frames!  The application may be doing too much work on its main thread.
05-14 13:40:04.982: I/Choreographer(4070): Skipped 47 frames!  The application may be doing too much work on its main thread.
05-14 13:40:05.673: I/Choreographer(4070): Skipped 144 frames!  The application may be doing too much work on its main thread.
05-14 13:40:05.823: I/Choreographer(4070): Skipped 36 frames!  The application may be doing too much work on its main thread.
05-14 13:40:05.962: I/Choreographer(4070): Skipped 32 frames!  The application may be doing too much work on its main thread.
05-14 13:40:06.162: I/Choreographer(4070): Skipped 45 frames!  The application may be doing too much work on its main thread.
05-14 13:40:06.334: I/Choreographer(4070): Skipped 40 frames!  The application may be doing too much work on its main thread.
05-14 13:40:07.313: I/Choreographer(4070): Skipped 77 frames!  The application may be doing too much work on its main thread.
05-14 13:40:07.453: I/Choreographer(4070): Skipped 32 frames!  The application may be doing too much work on its main thread.
05-14 13:40:07.672: I/Choreographer(4070): Skipped 52 frames!  The application may be doing too much work on its main thread.
05-14 13:40:08.244: I/Choreographer(4070): Skipped 35 frames!  The application may be doing too much work on its main thread.
05-14 13:40:08.382: I/Choreographer(4070): Skipped 34 frames!  The application may be doing too much work on its main thread.
05-14 13:40:08.853: I/Choreographer(4070): Skipped 98 frames!  The application may be doing too much work on its main thread.
05-14 13:40:09.052: I/Choreographer(4070): Skipped 33 frames!  The application may be doing too much work on its main thread.
05-14 13:40:09.644: I/Choreographer(4070): Skipped 35 frames!  The application may be doing too much work on its main thread.
05-14 13:40:10.083: I/Choreographer(4070): Skipped 39 frames!  The application may be doing too much work on its main thread.
05-14 13:40:10.413: I/Choreographer(4070): Skipped 48 frames!  The application may be doing too much work on its main thread.
05-14 13:40:10.582: I/Choreographer(4070): Skipped 38 frames!  The application may be doing too much work on its main thread.
05-14 13:40:10.922: I/Choreographer(4070): Skipped 42 frames!  The application may be doing too much work on its main thread.
05-14 13:40:11.062: I/Choreographer(4070): Skipped 34 frames!  The application may be doing too much work on its main thread.
05-14 13:40:11.312: I/Choreographer(4070): Skipped 58 frames!  The application may be doing too much work on its main thread.
05-14 13:40:11.452: I/Choreographer(4070): Skipped 32 frames!  The application may be doing too much work on its main thread.
05-14 13:40:11.634: I/Choreographer(4070): Skipped 44 frames!  The application may be doing too much work on its main thread.
05-14 13:40:12.072: I/Choreographer(4070): Skipped 36 frames!  The application may be doing too much work on its main thread.
05-14 13:40:12.222: I/Choreographer(4070): Skipped 35 frames!  The application may be doing too much work on its main thread.
05-14 13:40:12.422: I/Choreographer(4070): Skipped 48 frames!  The application may be doing too much work on its main thread.
05-14 13:40:12.622: I/Choreographer(4070): Skipped 47 frames!  The application may be doing too much work on its main thread.
05-14 13:40:12.763: I/Choreographer(4070): Skipped 32 frames!  The application may be doing too much work on its main thread.
05-14 13:40:13.033: I/Choreographer(4070): Skipped 42 frames!  The application may be doing too much work on its main thread.
05-14 13:40:13.193: I/Choreographer(4070): Skipped 37 frames!  The application may be doing too much work on its main thread.
05-14 13:40:13.532: I/Choreographer(4070): Skipped 54 frames!  The application may be doing too much work on its main thread.
05-14 13:40:13.682: I/Choreographer(4070): Skipped 36 frames!  The application may be doing too much work on its main thread.
05-14 13:40:13.882: I/Choreographer(4070): Skipped 47 frames!  The application may be doing too much work on its main thread.
05-14 13:40:14.092: I/Choreographer(4070): Skipped 45 frames!  The application may be doing too much work on its main thread.
05-14 13:40:14.573: I/Choreographer(4070): Skipped 59 frames!  The application may be doing too much work on its main thread.
05-14 13:40:14.922: I/Choreographer(4070): Skipped 47 frames!  The application may be doing too much work on its main thread.
05-14 13:40:15.292: I/Choreographer(4070): Skipped 32 frames!  The application may be doing too much work on its main thread.
05-14 13:40:16.284: I/Choreographer(4070): Skipped 44 frames!  The application may be doing too much work on its main thread.
05-14 13:40:16.442: I/Choreographer(4070): Skipped 33 frames!  The application may be doing too much work on its main thread.
05-14 13:40:16.632: D/Status:(4070): {"success":1,"login":[{"id":"1","company_id":"1","name":"Andre"}]}
05-14 13:40:16.852: I/Choreographer(4070): Skipped 33 frames!  The application may be doing too much work on its main thread.
05-14 13:40:17.103: D/AndroidRuntime(4070): Shutting down VM
05-14 13:40:17.133: W/dalvikvm(4070): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
05-14 13:40:17.222: E/AndroidRuntime(4070): FATAL EXCEPTION: main
05-14 13:40:17.222: E/AndroidRuntime(4070): java.lang.NullPointerException
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.content.ComponentName.<init>(ComponentName.java:75)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.content.Intent.<init>(Intent.java:3491)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at com.mobirep.app.Login$Check_Login$1.run(Login.java:170)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.os.Handler.handleCallback(Handler.java:725)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.os.Handler.dispatchMessage(Handler.java:92)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.os.Looper.loop(Looper.java:137)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at android.app.ActivityThread.main(ActivityThread.java:5041)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at java.lang.reflect.Method.invokeNative(Native Method)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at java.lang.reflect.Method.invoke(Method.java:511)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-14 13:40:17.222: E/AndroidRuntime(4070):     at dalvik.system.NativeStart.main(Native Method)

这是我的 login.java：

package com.mobirep.app;

import java.util.ArrayList;
import java.util.List;

import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class Login extends ActionBarActivity {

    //
    private static ProgressDialog pDialog;

    // Creating JSON Parser object
    JSONParser jParser = new JSONParser();
    static String TAG_SUCCESS = "success";
    String TAG_ID = "id";
    String TAG_NAME = "name";
    String TAG_COMPANY = "company_id";
    //buttons
     public static String Username;
     public static String Password;
     static String Name, Company_ID, ID;

    //

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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.login, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_login,
                    container, false);
            Button btnLogin = (Button) rootView.findViewById(R.id.btnLogin);
            btnLogin.setOnClickListener(new View.OnClickListener() {
              public void onClick(View v) {
                  EditText edtUsername = (EditText)getActivity().findViewById(R.id.edtUsername);
                  Username = edtUsername.getText().toString();
                  EditText edtPassword = (EditText)getActivity().findViewById(R.id.edtPassword);
                  Password = edtPassword.getText().toString();
                  // Toast for debugging purposes
                  pDialog = new ProgressDialog(getActivity());
                  pDialog.setMessage("Checking Details. Please wait...");
                  pDialog.setIndeterminate(false);
                  pDialog.setCancelable(false);
                  pDialog.show();
                  Login myActivity = new Login();
                  Login.Check_Login asyncTask = myActivity.new Check_Login();
                  asyncTask.execute();
            }
       });
            return rootView;
        }
    }


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

        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        /**
         * getting All products from url
         * */
        protected String doInBackground(String... args) {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("username", Username));
            params.add(new BasicNameValuePair("password", Password));
            // getting JSON string from URL
            JSONObject json = jParser.makeHttpRequest("http://mobirep.co.za/server_scripts/check_login/check_login.php", "GET", params);

            // Check your log cat for JSON reponse
            Log.d("Status: ", json.toString());

            try {
                // Checking for SUCCESS TAG
                int success = json.getInt("success");
                TAG_SUCCESS = json.getString("success");
                if (success == 1) {
                    JSONArray login_details_onj = json.getJSONArray("login");
                    JSONObject login_details = login_details_onj.getJSONObject(0);
                    // Get The Data
                    Name = login_details.getString(TAG_NAME);
                    ID = login_details.getString(TAG_ID);
                    Company_ID = login_details.getString(TAG_COMPANY);
                }
                else 
                {
                    TAG_NAME = json.getString("success");
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            runOnUiThread(new Runnable() {
                public void run() {
                    pDialog.dismiss();
                    Intent Select_company = new Intent(Login.this, Select_Company.class);
                    startActivity(Select_company);
                }
            });
        }
    }
}

Answer 1

public class Login extends ActionBarActivity {

Login 是一个活动类。您正在实例化一个 Activity 类 Login myActivity = new Login(); 这是错误的

你有

 Intent Select_company = new Intent(Login.this, Select_Company.class);
 startActivity(Select_company);

您需要一个有效的 Context 作为 Intent 构造函数的第一个参数，并且 startActivity 是 Activity 的一个方法。

继续阅读

Why do you have to pass this Context as a parameter in Android development?

您需要做的是将有效上下文从 Activity 传递给类的构造函数，并将上下文用作意图的第一个参数并使用 context.startActivtiy

编辑：

在 Fragment 中有这个

new Check_Login(getActivity()).execute(Username,Password);

然后将AsyncTask 类从Login 类移出到单独的.java 文件中

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

    Context context;
    ProgressDialog pDialog;
     static String TAG_SUCCESS = "success";
     String TAG_ID = "id";
     String TAG_NAME = "name";
     String TAG_COMPANY = "company_id";
     static String Name, Company_ID, ID;

    public Check_Login(Context context) {
        // TODO Auto-generated constructor stub
        this.context =context;
        pDialog = new ProgressDialog(context);
        pDialog.setMessage("Checking Details. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();

    }

    /**
     * Before starting background thread Show Progress Dialog
     * */

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    /**
     * getting All products from url
     * */
    protected String doInBackground(String... args) {
        // Building Parameters
         try {
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("username", args[0]));
        params.add(new BasicNameValuePair("password", args[1]));
        // getting JSON string from URL

        HttpClient client = new DefaultHttpClient(); 
        HttpPost httpGet = new HttpPost("http://mobirep.co.za/server_scripts/check_login/check_login.php"); 
        httpGet.setEntity(new UrlEncodedFormEntity(params));
        HttpResponse res = client.execute(httpGet);
        String jsonres = EntityUtils.toString(res.getEntity());

        JSONObject json = new JSONObject(jsonres);
        // Check your log cat for JSON reponse
        Log.d("Status: ", json.toString());


            // Checking for SUCCESS TAG
            int success = json.getInt("success");
            TAG_SUCCESS = json.getString("success");
            if (success == 1) {
                JSONArray login_details_onj = json.getJSONArray("login");
                JSONObject login_details = login_details_onj.getJSONObject(0);
                // Get The Data
                Name = login_details.getString(TAG_NAME);
                ID = login_details.getString(TAG_ID);
                Company_ID = login_details.getString(TAG_COMPANY);
            }
            else 
            {
                TAG_NAME = json.getString("success");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
    {
                pDialog.dismiss();
                Intent Select_company = new Intent(context, Select_Company.class);
                context.startActivity(Select_company);

    }
    }
}