Adding a View inside a ScrollView programmatically

Question

This is the xml code:

<LinearLayout 
    android:id="@+id/mainLayout"
    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"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:background="@color/black" >

    <ScrollView
        android:id="@+id/mainScrollView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/teal"
        android:layout_weight=".50">

     <LinearLayout
            android:id="@+id/linearLayout1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" >

     </LinearLayout>


    </ScrollView>

    <Button 
         android:id="@+id/addButton"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="+"
         android:gravity="center"
         android:layout_weight=".20"
     />

     <TextView
         android:id="@+id/totalHoursLabel"
         android:text="Ore Totali"
         android:background="@color/gray"
         android:textColor="@color/red"
         android:gravity="center"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_weight=".10"
     />

     <TextView
         android:id="@+id/totalHoursView"
         android:text="00:00"
         android:background="@color/white"
         android:textColor="@color/black"
         android:gravity="center"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_weight=".20"
     />

</LinearLayout>

My problem is that when I try to add a view to the ScrollView or his inner LinearLayout my program crashes.

Here is my java code:

super.onCreate(savedInstanceState);

LinearLayout ll = (LinearLayout) findViewById(R.id.linearLayout1);

TextView tv = new TextView(this);
tv.setText("testView");
tv.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
ll.addView(tv);

setContentView(R.layout.activity_main);

If I create a new android project this code (with only a relativeLayout and everything else empty in the xml file) works fine.

I think that there is some problem with the findViewById method or my xml file.

Any ideas?

This is my LogCat file:

07-23 15:56:19.119: D/AndroidRuntime(1249): Shutting down VM
07-23 15:56:19.119: W/dalvikvm(1249): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
07-23 15:56:19.159: E/AndroidRuntime(1249): FATAL EXCEPTION: main
07-23 15:56:19.159: E/AndroidRuntime(1249): java.lang.RuntimeException: Unable to start activity ComponentInfo{workTimer.worktimer/workTimer.worktimer.MainActivity}: java.lang.NullPointerException
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.os.Looper.loop(Looper.java:137)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.ActivityThread.main(ActivityThread.java:5041)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at java.lang.reflect.Method.invokeNative(Native Method)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at java.lang.reflect.Method.invoke(Method.java:511)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at dalvik.system.NativeStart.main(Native Method)
07-23 15:56:19.159: E/AndroidRuntime(1249): Caused by: java.lang.NullPointerException
07-23 15:56:19.159: E/AndroidRuntime(1249):     at workTimer.worktimer.MainActivity.onCreate(MainActivity.java:32)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.Activity.performCreate(Activity.java:5104)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-23 15:56:19.159: E/AndroidRuntime(1249):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-23 15:56:19.159: E/AndroidRuntime(1249):     ... 11 more
07-23 15:56:22.649: I/Process(1249): Sending signal. PID: 1249 SIG: 9

Solution

You have to call setContentView before you can call findViewById, so your code will be:

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

LinearLayout ll = (LinearLayout) findViewById(R.id.linearLayout1);

TextView tv = new TextView(this);
tv.setText("testView");
tv.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
ll.addView(tv);