Question

There is an error occurring in an app of mine when I set an Adapter to a ListView. Upon removing the 60/61 line of code (mainListViewTip/Hour.setAdapter(tip/hourAdapter);), the application runs perfectly, except since the adapter is never set, no data appears in the ListView. The goal is for the values of the EditText fields to become new values in the String to be displayed in a ListView along with previous entries also.

The TipBookActivity code:

public class TipBookActivity extends Activity {
/** Called when the activity is first created. */

TextView textTip,textHour,textWage;
EditText editHour,editTip;
float wage;
int precision = 100;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);  
    textTip = (TextView) findViewById(R.id.tvTip);
    textHour = (TextView) findViewById(R.id.tvHour);
    textWage = (TextView) findViewById(R.id.tvWage);
    editTip = (EditText) findViewById(R.id.etTip);
    editHour = (EditText) findViewById(R.id.etHour);
}

public void myClickHandler (View v){
    Button bSubmit = (Button) findViewById(R.id.bSubmit);
    bSubmit.isClickable();
    ListView mainListViewTip = (ListView) findViewById(R.id.mainListViewTip);
    ListView mainListViewHour = (ListView) findViewById(R.id.mainListViewHour);
    switch(v.getId()){
    case R.id.bSubmit:
        if(bSubmit.isPressed()){
            wage = Float.parseFloat(editTip.getText().toString()) / Float.parseFloat(editHour.getText().toString());
            String tip = String.format("$%.2f",wage);
            textWage.setText(String.valueOf(tip) + " an hour");     
            textHour.setText(editHour.getText() + " Hour(s)");
            textTip.setText("$" + editTip.getText());
            String[] sTip = new String[] {editTip.getText().toString()};
            String[] sHour = new String[] {editHour.getText().toString()};
            ArrayAdapter<String> tipAdapter = new ArrayAdapter<String>(TipBookActivity.this,R.layout.main,R.id.rowTextView,sTip);
            ArrayAdapter<String> hourAdapter = new ArrayAdapter<String>(TipBookActivity.this,R.layout.main,R.id.rowTextView,sHour);
            mainListViewTip.setAdapter(tipAdapter);
            mainListViewHour.setAdapter(hourAdapter);
            Toast displayWage = Toast.makeText(this, "$" + editTip.getText() + " over " + editHour.getText() + " hour(s) for a wage of $" + wage + " an hour.", Toast.LENGTH_LONG);
            displayWage.show();
        }
    }
}
public boolean onCreateOptionsMenu(Menu menu){
    super.onCreateOptionsMenu(menu);
    MenuInflater mMain = getMenuInflater();
    mMain.inflate(R.menu.main_menu,menu);
    return true;
}

public boolean onOptionsItemSelected(MenuItem item){
    ViewFlipper vf = (ViewFlipper) findViewById(R.id.vfMain);
    switch (item.getItemId()){
    case R.id.menuHistory:
         vf.setAnimation(AnimationUtils.loadAnimation(this, R.anim.slide_in_right));
         vf.showNext();
         return true;
    case R.id.menuClear:
        //set up next tutorials
        Toast displayClear = Toast.makeText(this, "Clear History feature coming soon.", Toast.LENGTH_SHORT);
        displayClear.show();
        return true;
    case R.id.menuSettings:
        Toast displaySettings = Toast.makeText(this, "Settings Options coming soon.", Toast.LENGTH_SHORT);
        displaySettings.show();
        return true;
    }
    return false;
}

public void onBackPressed() {
    finish();
    }
}   

The main xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="@+id/llMain" >

<ViewFlipper
    android:id="@+id/vfMain"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/rletbtv">      

            <EditText 
                android:id="@+id/etTip"
                android:layout_height="wrap_content"
                android:layout_width="140dp"
                android:hint="Tips"
                android:layout_margin="8dp"
                android:inputType="numberDecimal"
                android:layout_alignParentLeft="true"/>

            <EditText
                    android:id="@+id/etHour"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content"
                android:hint="Hours"
                android:layout_margin="8dp"
                android:inputType="numberDecimal"
                android:layout_alignParentRight="true"
                android:layout_toRightOf="@id/etTip"/>

            <Button
                android:id="@+id/bSubmit"
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:layout_margin="8dp"
                android:ems="10"
                android:text="Submit"
                android:textSize="22sp"
                android:layout_below="@id/etTip"
                android:onClick="myClickHandler"/>

            <TextView
                android:id="@+id/tvTip"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content"
                android:text="Tips"
                android:textSize="22sp"
                android:layout_margin="8dp"
                android:layout_below="@id/bSubmit"/>

            <TextView
                android:id="@+id/tvHour"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content"
                android:text="Hours"
                android:textSize="22sp"
                android:layout_margin="8dp"
                android:layout_below="@id/bSubmit"
                android:layout_toRightOf="@id/tvTip"/>

            <TextView
                android:id="@+id/tvWage"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content"
                android:text="Wage"
                android:textSize="22sp"
                android:layout_margin="8dp"
                android:layout_below="@id/bSubmit"
                android:layout_toRightOf="@id/tvHour"/>

        </RelativeLayout>
    </LinearLayout>
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="vertical" >

        <ListView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="50"
            android:id="@+id/mainListViewTip"/>

        <ListView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="50" 
            android:id="@+id/mainListViewHour"/>

</LinearLayout>
</ViewFlipper>
</LinearLayout>

The simplerow xml file:

<?xml version="1.0" encoding="utf-8"?>

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/rowTextView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:padding="10dp"
android:textSize="16sp" />

The logcat error report:

FATAL EXCEPTION: main
java.lang.NullPointerException
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:353)
at android.widget.ArrayAdapter.getView(ArrayAdapter.java:323)
at android.widget.AbsListView.obtainView(AbsListView.java:1315)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1198)
at android.widget.ListView.onMeasure(ListView.java:1109)
at android.view.View.measure(View.java:8171)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1012)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:381)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
at android.view.View.measure(View.java:8171)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
at android.view.View.measure(View.java:8171)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1012)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:381)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
at android.view.View.measure(View.java:8171)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
at android.view.View.measure(View.java:8171)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:526)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
at android.view.View.measure(View.java:8171)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
at android.view.View.measure(View.java:8171)
at android.view.ViewRoot.performTraversals(ViewRoot.java:801)
at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4627)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)

Answer 1

The problem is because the layout you are passing to the ArrayAdapter is R.layout.main. This is not the resource you want to pass; you want to pass the layout for each individual list item. The layout you pass must have a TextView with a certain ID in it, and obviously R.layout.main does not have this.

Try substituting R.layout.main in those two lines to be android.R.layout.simple_list_item_1, and removing your custom TextView ID. That should solve the error and allow your list to display properly.

Like so:

ArrayAdapter<String> tipAdapter = new ArrayAdapter<String>(TipBookActivity.this,android.R.layout.simple_list_item_1,sTip);
ArrayAdapter<String> hourAdapter = new ArrayAdapter<String>(TipBookActivity.this,android.R.layout.simple_list_item_1,sHour);

If you later want to use a custom layout for the list items, try this tutorial or this one.