Android app crashes when showing/hiding visiblity of ImageView

Question

I've been trying to create my first android app, and yes... got stuck up with an app crash...

I had two ImageViews in my fragment (main), overlapping imageview 1 with imageview2 in a relative layout. What I wanted to do was, imageview1 (not imageview 2) should be showing up if there's an Internet connection. and vice versa if no internet connection. As per a tutorial, i created a separate class for detecting connection:

   package com.mypackage.myapp;

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;

public class ConnectionDetector {

    private Context _context;

    public ConnectionDetector(Context context){
        this._context = context;
    }

    public boolean isConnectingToInternet(){
        ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);
          if (connectivity != null)
          {
              NetworkInfo[] info = connectivity.getAllNetworkInfo();
              if (info != null)
                  for (int i = 0; i < info.length; i++)
                      if (info[i].getState() == NetworkInfo.State.CONNECTED)
                      {
                          return true;
                      }

          }
          return false;
    }
}

And called up the class in my mainactivity.class, made an if statement for two instances of connection (connected/disconnected) with a boolean variable... finally, i used setVisibility() for each ImageViews in the if statement in onCreate(). here's the code:

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    } 
    Intent cd = getIntent();
    ConnectionDetector cdr = new ConnectionDetector(getApplicationContext());
    boolean isInternetPresent = cdr.isConnectingToInternet();
    ImageView glss2 = (ImageView)findViewById(R.id.glass2);
    ImageView glss1 = (ImageView) findViewById(R.id.glass1);
    if (isInternetPresent) {
        glss1.setVisibility(View.VISIBLE);
        glss2.setVisibility(View.GONE);
    } else {
       glss1.setVisibility(View.GONE);
       glss2.setVisibility(View.VISIBLE);
    }
}

Additionally, if you want my layout file:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:background="@drawable/backrepeatlinen"
tools:context="com.mypackage.myapp.MainActivity$PlaceholderFragment" >

<ImageView
    android:id="@+id/glass1"
    android:layout_width="160dp"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:src="@drawable/glass" android:contentDescription="@string/hello_world"/>

<ImageView
    android:id="@+id/glass2"
    android:layout_width="150dp"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/glass1"
    android:layout_centerHorizontal="true"
    android:contentDescription="@string/hello_world"
    android:src="@drawable/broken" />

Everytime, when I run the program in my tablet, it crashes at the activity. i tried removing the connection detector and if statement thing, the activity moves well.

Edit: the only problem is on the setVisiblity() in the if statement, because when removing it, everything else works properly. Is it possible to solve? or can we controll the visiblity of two imageviews with a different method?.

logcat:

05-21 11:05:38.432: E/filePathInTheme(23435): fallback to res
05-21 11:05:38.462: E/filePathInTheme(23435): fallback to res
05-21 11:05:38.482: E/filePathInTheme(23435): fallback to res
05-21 11:05:38.652: E/filePathInTheme(23435): fallback to res
05-21 11:05:38.802: I/Adreno200-EGLSUB(23435): <ConfigWindowMatch:2081>: Format RGBA_8888.
05-21 11:05:38.812: D/memalloc(23435): /dev/pmem: Mapped buffer base:0x50c32000 size:11960320 offset:10485760 fd:54
05-21 11:05:39.122: D/memalloc(23435): /dev/pmem: Mapped buffer base:0x51a3b000 size:13434880 offset:11960320 fd:57
05-21 11:05:41.542: E/filePathInTheme(23435): fallback to res
05-21 11:05:41.572: W/dalvikvm(23435): threadid=1: thread exiting with uncaught exception (group=0x40a659f0)
05-21 11:05:41.582: E/AndroidRuntime(23435): FATAL EXCEPTION: main
05-21 11:05:41.582: E/AndroidRuntime(23435): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lemonaade.watchr/com.lemonaade.watchr.MainActivity}: java.lang.NullPointerException
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1961)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1986)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1152)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.os.Looper.loop(Looper.java:137)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.ActivityThread.main(ActivityThread.java:4450)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at java.lang.reflect.Method.invokeNative(Native Method)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at java.lang.reflect.Method.invoke(Method.java:511)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at dalvik.system.NativeStart.main(Native Method)
05-21 11:05:41.582: E/AndroidRuntime(23435): Caused by: java.lang.NullPointerException
05-21 11:05:41.582: E/AndroidRuntime(23435):    at com.lemonaade.watchr.MainActivity.onCreate(MainActivity.java:35)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.Activity.performCreate(Activity.java:4465)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-21 11:05:41.582: E/AndroidRuntime(23435):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1925)
05-21 11:05:41.582: E/AndroidRuntime(23435):    ... 11 more

thanks.

I have shortlisted my problem, and i uploaded my logcat too. — abilashsenth, May 21 '14 at 07:11

score 1 · Answer 1 · answered May 20 '14 at 08:17

1

You should move

ImageView glss1 = (ImageView) findViewById(R.id.glass1);
ImageView glss2 = (ImageView)findViewById(R.id.glass2);

under onCrete(....) after setContentView(R.layout.activity_main);

answered May 20 '14 at 08:17

M D

47,665
9
93
114

score 1 · Answer 2 · answered May 20 '14 at 08:18

1

please move this code below setContentView().

ImageView glss1 = (ImageView) findViewById(R.id.glass1);
ImageView glss2 = (ImageView)findViewById(R.id.glass2);

You are finding view before you set the content of the view. thats why it is not working.

answered May 20 '14 at 08:18

Waqar Ahmed

5,005
2
23
45

score 0 · Answer 3 · edited May 23 '17 at 10:26

0

Since the layout is your fragment layout and not activity layout, the solution from a couple of other answers of moving the findViewById() to onCreate() after setContentView() still won't work.

Instead, move the code to the PlaceholderFragment onCreateView(), using getActivity() for Context and calling rootView.findViewById() on the inflated rootView layout.

See NullPointerException accessing views in onCreate() for more.

edited May 23 '17 at 10:26

Community

1
1

answered May 20 '14 at 08:20

laalto

150,114
66
286
303

it's not by default, present on my code (onCreateView()...) so should i add it? if so, can i do it below onCreate? edit:i found it in placeholder fragment – abilashsenth May 20 '14 at 08:30
Looks like the code is generated from a template and the template/wizard generated PlaceholderFragment onCreateView(), too. – laalto May 20 '14 at 08:42
but eclipse says cannot make static refrence to non static method for ConnectionDetector(getApplicationContext());, and two findViewById()...` – abilashsenth May 20 '14 at 08:53
In a fragment, use `getActivity()` for a `Context` and call `findViewById()` on the inflated `rootView`. – laalto May 20 '14 at 08:58
got the getActivity() right, but i've already placed the findViewById() after View rootView = inflater.inflate(R.layout.fragment_main, container, false); – abilashsenth May 20 '14 at 09:11

score 0 · Answer 4 · answered May 20 '14 at 08:27

Write the code to the fragment onCreateView() of PlaceholderFragment() after inflating your xml .

ImageView glss1 = (ImageView) findViewById(R.id.glass1);
ImageView glss2 = (ImageView)findViewById(R.id.glass2);

Make sure you have added Following Permission in your Manifest file

 <uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Android app crashes when showing/hiding visiblity of ImageView

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