getting an error while starting normal main activity

Question

I am currently breaking my head off, because I can start a normal startActivity(). It is always giving me this error:

Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference

I am starting it from my Application Welcome Activity:

application.getUserFromDatabase(getApplicationContext(), username, password);

Application:

public void getUserFromDatabase(Context context, String username, String password) {
   //new GetFromDatabase().execute("getUser.php", "?username=" + username + "&password=" + password, this, context);
    WelcomeActivity activity = new WelcomeActivity();
    activity.startMainActivity();
}

AndroidManifest:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.mydomain.app">

    <application
        android:name=".MainApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">

        </activity>
        <activity android:name=".WelcomeActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Thank you in advance :)

EDIT: I forgot adding my Method startMainActivity here:

public void startMainActivity(){
    Intent startMain = new Intent(getApplicationContext(), MainActivity.class)
    startActivity(startMain);
}

Can you provide more detail on the code under WelcomeActivity activity = new WelcomeActivity(); activity.startMainActivity(); what's the code inside startMainActivity — Brijesh Joshi, May 05 '18 at 08:30
In addition to @Farrokh Shahriari's answer below, you cant's start an activity using the application context. You need to give the activity/service context when creating an intent. — Rishabh Jain, May 05 '18 at 08:54

score 0 · Answer 1 · answered May 05 '18 at 08:34

0

you must use intent for startActivity();

example:

 Intent intent = new Intent(this, WelcomeActivity.class);
 startActivtiy(intent);

answered May 05 '18 at 08:34

Farrokh Shahriari

377
2
10

score 0 · Answer 2 · answered May 05 '18 at 08:58

It definitely causing you a null pointer exception because your WelcomeActivity is not created yet. You can't start an activity by creating a new instance of Activity with:

WelcomeActivity activity = new WelcomeActivity();

Your activity need to be start with:

Intent welcome = new Intent(context, WelcomeActivity.class);
context.startActivtiy(welcome);

or by adding the correct intent-filter so the activity will be launched by the Android system.

You can start your activity from Application with something like this:

// FLAG_ACTIVITY_NEW_TASK is required
// FLAG_ACTIVITY_CLEAR_TOP brings back to the top of the stack
Intent mainActivity = new Intent(this, MainActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(mainActivity);

Though I think you should not start an Activity via Application. You need to think throughly about your design so there is no activity connection with the application.

getting an error while starting normal main activity

2 Answers2