how to switch activity properly without android launcher shooting down

[nida azizah]

hi, I'm working in a project which need to show my MainActivity after i run several java class. i need to run bluetooth> register > MainActivity. MainActivity is the only activity that contain layout. because Bluetooth and register doesn't have layout, i deleted this

setContentView(R.layout.activity_bluetooth); 

and

setContentView(R.layout.activity_register)

;. I also put intent in my program to refer one activity to another. After that i change my AndroidManifest stuctured like this :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.windows8.registerlogin">
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

    <application
        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=".Bluetooth" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

after i open the program, it shut down immediately. can you tell me how to switch activity properly without android launcher shooting down? thank you for your help.

[Tim Moores]

Whenever an activity crashes, the full stack trace is written to the logcat - post it here (NOT the entire content of the logcat, just the relevant bits).

[nida azizah]

here's the logcat :

07-14 17:57:35.974 15820-15820/com.example.windows8.registerlogin E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.windows8.registerlogin, PID: 15820
    java.lang.RuntimeException: Unable to start activity ComponentInfo
{com.example.windows8.registerlogin/com.example.windows8.registerlogin.Bluetooth}:
 java.lang.NullPointerException: Attempt to invoke virtual method 
'void android.widget.TextView.append(java.lang.CharSequence)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2505)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2577)
        at android.app.ActivityThread.access$1000(ActivityThread.java:164)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:159)
        at android.app.ActivityThread.main(ActivityThread.java:5541)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:975)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:770)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 
'void android.widget.TextView.append(java.lang.CharSequence)' on a null object reference
        at com.example.windows8.registerlogin.Bluetooth.CheckBTState(Bluetooth.java:191)
        at com.example.windows8.registerlogin.Bluetooth.onCreate(Bluetooth.java:48)
        at android.app.Activity.performCreate(Activity.java:6093)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2458)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2577) 
        at android.app.ActivityThread.access$1000(ActivityThread.java:164) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:159) 
        at android.app.ActivityThread.main(ActivityThread.java:5541) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:975) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:770)

[nida azizah]

I forget something, i'm also using sqlitedatabase in DatabaseHelper Activity but i can't insert it to AndroidManifest, so i didn't do that. I hope it doesn't cause any problem.

[Norm Radder]

 

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.append(java.lang.CharSequence)' on a null object reference
       at com.example.windows8.registerlogin.Bluetooth.CheckBTState(Bluetooth.java:191)

What variable/value is null on line 191?

[Tim Moores]

nida azizah wrote:i'm also using sqlitedatabase in DatabaseHelper Activity but i can't insert it to AndroidManifest, so i didn't do that.

You mean the <provider> element? Why not? That sure sounds like it could cause problems. Also tell us which object is null when you try to call "append" on it, and why.

[Swastik Dey]

TextView.append

Probably the text view being referred is not inflated from the referred layout xml file properly.