NullPointerException at startActivity(intent)

Question

For the life of me, I can't seem to find out what's wrong with my code.

AgrUserLoginHome.java public void onClick(View v) { if(v.getId()==R.id.btnSubmitLogin) { String username=txtUsername.getText().toString(); String password=txtPassword.getText().toString(); //this is passed to be used in next LoginClientServiceThread class LoginClientServiceThread verifyLog = new LoginClientServiceThread(this,username,password); verifyLog.run(); } }

LoginClientServiceThread.java

 public class LoginClientServiceThread extends Activity implements Runnable{ private Intent intent; private String username,password; private Context context; public LoginClientServiceThread(Context cont,String user,String pass) { username=user; password=pass; context=cont; } public void run() { try { try { JSONObject json = new JSONObject(); json.put("username", username); json.put("password", password); DefaultHttpClient httpClient = new DefaultHttpClient(); URI uri = new URI("http://10.0.2.2:80/BairyApp/Login.svc"); HttpPost httppost = new HttpPost(uri + "/verifyLogin"); httppost.setHeader("Accept", "application/json"); httppost.setHeader("Content-type", "application/json; charset=utf-8"); HttpResponse response = httpClient.execute(httppost); HttpEntity responseEntity = response.getEntity(); long intCount = responseEntity.getContentLength(); char[] buffer = new char[(int)intCount]; InputStream stream = responseEntity.getContent(); InputStreamReader reader = new InputStreamReader(stream, "UTF-8"); try { reader.read(buffer); String str = new String(buffer); intent=new Intent(context,TrainerAccessScreen.class); intent.putExtra("reading",str); if(null!=intent) { Toast.makeText(context, "Working", Toast.LENGTH_LONG).show(); //startActivity shows as null here startActivity(intent); } Toast.makeText(context, str, Toast.LENGTH_SHORT).show(); } catch (IOException e) { e.printStackTrace(); Toast.makeText(context, "IOException:"+e.getMessage(), Toast.LENGTH_LONG).show(); } finally { stream.close(); } } catch(URISyntaxException urise) { urise.printStackTrace(); Toast.makeText(context, "urise", Toast.LENGTH_LONG).show(); } catch(ClientProtocolException cpe) { cpe.printStackTrace(); Toast.makeText(context, "cpe", Toast.LENGTH_LONG).show(); } catch(IOException ioe) { ioe.printStackTrace(); Toast.makeText(context, "ioe", Toast.LENGTH_LONG).show(); } } catch(Exception e) { Toast.makeText(context, "Execution failed: "+e.getMessage(), Toast.LENGTH_SHORT).show(); e.printStackTrace(); } } }

I'm sure the startActivity method is returning a null. I know this because if i change the intent context to "this", the Toast in the IOException directly below it doesn't show.

Any ideas? Oh btw, I'm a beginner so I know the code looks horrible

LogCat

10-26 20:28:48.756: I/dalvikvm(1133): Jit: resizing JitTable from 512 to 1024 10-26 20:41:57.906: W/System.err(1169): java.lang.NullPointerException 10-26 20:41:57.906: W/System.err(1169): at android.app.Activity.startActivityForResult(Activity.java:2827) 10-26 20:41:57.906: W/System.err(1169): at android.app.Activity.startActivity(Activity.java:2933) 10-26 20:41:57.916: W/System.err(1169): at agr.mobile.service.LoginClientServiceThread.run(LoginClientServiceThread.java:76) 10-26 20:41:57.916: W/System.err(1169): at agr.mobile.app.AgrUserLoginHome.onClick(AgrUserLoginHome.java:59) 10-26 20:41:57.916: W/System.err(1169): at android.view.View.performClick(View.java:2485) 10-26 20:41:57.916: W/System.err(1169): at android.view.View$PerformClick.run(View.java:9080) 10-26 20:41:57.916: W/System.err(1169): at android.os.Handler.handleCallback(Handler.java:587) 10-26 20:41:57.916: W/System.err(1169): at android.os.Handler.dispatchMessage(Handler.java:92) 10-26 20:41:57.916: W/System.err(1169): at android.os.Looper.loop(Looper.java:123) 10-26 20:41:57.916: W/System.err(1169): at android.app.ActivityThread.main(ActivityThread.java:3683) 10-26 20:41:57.916: W/System.err(1169): at java.lang.reflect.Method.invokeNative(Native Method) 10-26 20:41:57.916: W/System.err(1169): at java.lang.reflect.Method.invoke(Method.java:507) 10-26 20:41:57.916: W/System.err(1169): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 10-26 20:41:57.926: W/System.err(1169): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 10-26 20:41:57.926: W/System.err(1169): at dalvik.system.NativeStart.main(Native Method)

The LoginClientServiceThread.java file is not an activity file. It's just a plain java class meant to do the service operations outside of the activity classes — Zubair
– Zubair, Commented Oct 26, 2012 at 18:47

Raghav Sood · Accepted Answer · 2012-10-26 18:53:02Z

You say that LoginClientServiceThread isn't an Activity, yet you extend Activity. Don't do this. If you want to launch an Activity from a non-Activity class, use the following:

intent=new Intent(context,TrainerAccessScreen.class); intent.putExtra("reading",str); if(null!=intent) { Toast.makeText(context, "Working", Toast.LENGTH_LONG).show(); context.startActivity(intent); }

You're getting a NullPointerException as you're calling startActivity() from the this instance of LoginClientServiceThread. However, as you haven't launched and created that Activity as a normal Activity, you have a null reference. So your final code will look like:

public class LoginClientServiceThread implements Runnable{ private Intent intent; private String username,password; private Context context; public LoginClientServiceThread(Context cont,String user,String pass) { username=user; password=pass; context=cont; } public void run() { try { try { JSONObject json = new JSONObject(); json.put("username", username); json.put("password", password); DefaultHttpClient httpClient = new DefaultHttpClient(); URI uri = new URI("http://10.0.2.2:80/BairyApp/Login.svc"); HttpPost httppost = new HttpPost(uri + "/verifyLogin"); httppost.setHeader("Accept", "application/json"); httppost.setHeader("Content-type", "application/json; charset=utf-8"); HttpResponse response = httpClient.execute(httppost); HttpEntity responseEntity = response.getEntity(); long intCount = responseEntity.getContentLength(); char[] buffer = new char[(int)intCount]; InputStream stream = responseEntity.getContent(); InputStreamReader reader = new InputStreamReader(stream, "UTF-8"); try { reader.read(buffer); String str = new String(buffer); intent=new Intent(context,TrainerAccessScreen.class); intent.putExtra("reading",str); if(null!=intent) { Toast.makeText(context, "Working", Toast.LENGTH_LONG).show(); //startActivity shows as null here context.startActivity(intent); } Toast.makeText(context, str, Toast.LENGTH_SHORT).show(); } catch (IOException e) { e.printStackTrace(); Toast.makeText(context, "IOException:"+e.getMessage(), Toast.LENGTH_LONG).show(); } finally { stream.close(); } } catch(URISyntaxException urise) { urise.printStackTrace(); Toast.makeText(context, "urise", Toast.LENGTH_LONG).show(); } catch(ClientProtocolException cpe) { cpe.printStackTrace(); Toast.makeText(context, "cpe", Toast.LENGTH_LONG).show(); } catch(IOException ioe) { ioe.printStackTrace(); Toast.makeText(context, "ioe", Toast.LENGTH_LONG).show(); } } catch(Exception e) { Toast.makeText(context, "Execution failed: "+e.getMessage(), Toast.LENGTH_SHORT).show(); e.printStackTrace(); } } }

You don't need to extend Activity at all in the second class.

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