Question

Could I get a NullPointerException because the button I am referencing is nested inside several layouts? Any time I reference browseEditBtn I get an exception. It’s a simple button! Come’on.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

 android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
>
<TableLayout 
android:layout_width="wrap_content" 
android:layout_height="wrap_content"
android:orientation="horizontal" 
android:stretchColumns="*">
<!-- <include layout="@layout/mydesctextview" /> -->
<TableRow 
android:id="@+id/tableRow1" 
android:layout_width="wrap_content"
android:layout_height="wrap_content" 
android:orientation="horizontal">

        <TextView 
        android:text="TextView" 
        android:layout_width="wrap_content"
        android:layout_gravity="left|center_vertical" 
        android:id="@+id/txtItem" 
        android:textSize="20dip" 

        ></TextView>



        <ImageButton

        android:src="@drawable/editbtn"
        android:layout_marginRight="10dip" 
        android:layout_gravity="right|center_vertical"
        android:id="@+id/browseEditBtn"
        android:background="@drawable/my_group_statelist"
        ></ImageButton>

</TableRow>
</TableLayout>
</LinearLayout>

Source Code (The Button is called in the main onCreate()):

public class BrowseActivity extends ExpandableListActivity {

final private String[] asColumnsToReturn = {
        Items.ITEMS_TABLE_NAME + "." + Items.ITEMS_ITEM,
        Items.ITEMS_TABLE_NAME + "." + Items.ITEMS_DESC,
        Items.ITEMS_TABLE_NAME + "." + Items.ITEMS_MANU,
        Items.ITEMS_TABLE_NAME + "." + Items.ITEMS_ID };

@SuppressWarnings("unchecked")
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.browse);
    DbHelper dbh = new DbHelper(this.getApplicationContext());
    SQLiteDatabase db = dbh.getWritableDatabase();
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    queryBuilder.setTables(Items.ITEMS_TABLE_NAME);

    ExpandableListView browseView = (ExpandableListView)    findViewById(android.R.id.list);
    Button editBrowseBtn = (Button) findViewById(R.id.browseEditBtn);

    Cursor mCursor = queryBuilder.query(db, asColumnsToReturn, null, null,
            null, null, Items.DEFAULT_SORT_ORDER);
    startManagingCursor(mCursor);

    SimpleExpandableListAdapter mAdapter = new SimpleExpandableListAdapter(
            this, createGroup(), R.layout.row, R.layout.row, new String[] {
                    Items.ITEMS_ITEM, Items.ITEMS_DESC }, new int[] {
                    R.id.txtItem, R.id.dscItem }, createChildren(),
            R.layout.exprow, new String[] { Items.ITEMS_DESC,
                    Items.ITEMS_MANU }, new int[] { R.id.dscItem,
                    R.id.manuItem });
    browseView.setAdapter(mAdapter);

    editBrowseBtn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Intent intent = new Intent(BrowseActivity.this,
                    EditItemActivity.class);
            startActivity(intent);

        }
    });

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);
    menu.add("Add Item").setIntent(new Intent(this, AddItemActivity.class));

    return super.onCreateOptionsMenu(menu);
}

@SuppressWarnings("rawtypes")
public List createGroup() {
    DbHelper dbh = new DbHelper(this.getApplicationContext());
    SQLiteDatabase db = dbh.getWritableDatabase();
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    queryBuilder.setTables(Items.ITEMS_TABLE_NAME);

    Cursor mCursor = queryBuilder.query(db, new String[] {
            Items.ITEMS_ITEM, Items.ITEMS_DESC }, null, null, null, null,
            Items.DEFAULT_SORT_ORDER);
    startManagingCursor(mCursor);

    ArrayList<HashMap<String, String>> groupList = new ArrayList<HashMap<String,   String>>();
    mCursor.moveToFirst();
    while (!(mCursor.isAfterLast())) {

        HashMap<String, String> groupMap = new HashMap<String, String>();
        groupMap.put(Items.ITEMS_ITEM,
                mCursor.getString(mCursor.getColumnIndex(Items.ITEMS_ITEM)));
        groupMap.put(Items.ITEMS_DESC,
                      mCursor.getString(mCursor.getColumnIndex(Items.ITEMS_DESC)));

        groupList.add(groupMap);
        mCursor.moveToNext();
    }

    return (List) groupList;
}

@SuppressWarnings("rawtypes")
public List createChildren() {
    DbHelper dbh = new DbHelper(this.getApplicationContext());
    SQLiteDatabase db = dbh.getWritableDatabase();
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
    queryBuilder.setTables(Items.ITEMS_TABLE_NAME);

    Cursor mCursor = queryBuilder.query(db, new String[] {
            Items.ITEMS_ITEM, Items.ITEMS_DESC, Items.ITEMS_MANU }, null,
            null, null, null, Items.DEFAULT_SORT_ORDER);
    startManagingCursor(mCursor);
    mCursor.moveToFirst();

    ArrayList<ArrayList<HashMap<String, String>>> childList = new ArrayList<ArrayList<HashMap<String, String>>>();

    while (!(mCursor.isAfterLast())) {

        ArrayList<HashMap<String, String>> childListDesc = new                      ArrayList<HashMap<String, String>>();

        for (int i = 0; i < 1; i++) {
            HashMap<String, String> childMap = new HashMap<String, String>();
            childMap.put(Items.ITEMS_DESC, mCursor.getString(mCursor
                    .getColumnIndex(Items.ITEMS_DESC)));
            childMap.put(Items.ITEMS_MANU, mCursor.getString(mCursor
                    .getColumnIndex(Items.ITEMS_MANU)));

            childListDesc.add(childMap);

        }

        childList.add(childListDesc);
        mCursor.moveToNext();
    }

    return (List) childList;
}
}

And finally the logcat, I think…

06-30 13:01:29.390: ERROR/AndroidRuntime(9189): FATAL EXCEPTION: main
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.simplyDesign.mdk/com.simplyDesign.mdk.BrowseActivity}: java.lang.NullPointerException
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.os.Handler.dispatchMessage(Handler.java:99)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.os.Looper.loop(Looper.java:123)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.ActivityThread.main(ActivityThread.java:4627)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at java.lang.reflect.Method.invokeNative(Native Method)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at java.lang.reflect.Method.invoke(Method.java:521)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at dalvik.system.NativeStart.main(Native Method)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): Caused by: java.lang.NullPointerException
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at com.simplyDesign.mdk.BrowseActivity.onCreate(BrowseActivity.java:62)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
06-30 13:01:29.390: ERROR/AndroidRuntime(9189): … 11 more

edit_01

public void doAction(View v) {

    startActivity(new Intent(getApplicationContext(),
            EditItemActivity.class));

}

I have used other buttons in the past to point to EditItemActivity and they have worked fine.

Answer 1

What is the name of the layout XML file that you posted? It doesn’t appear to be browse.xml because that one has your ExpandableListView in it. The IDs that you reference in your Java code must appear in the content View that you set; otherwise, you must inflate the View yourself.

Edit

You would add something like

android:onClick="doAction"

to the XML of that ImageButton.

Then you would have a doAction(View v) method in your Activity that would do your onClick actions.