Android: NumberPicker doesn´t work

Question

I added a NumberPicker to my layout and debugged my app. Now I see that the NumberPicker doesn´t work, I can´t see any "+" or "-" button and also when I click on a number on my keyboard, nothing happens.

Here´s my layout file:

<RelativeLayout 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"
android:background="#99cc00"
tools:context=".Gewichtsentwicklung" >

<NumberPicker
    android:id="@+id/numberPicker1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="80dp" />

<TextView
    android:id="@+id/tvGewichtUeberschrift"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:layout_centerHorizontal="true"
    android:textColor="@color/white"
    android:textSize="13pt"
    android:layout_alignParentTop="true"
    android:text="Aktuelles Gewicht eingeben" />

<Button
    android:id="@+id/btGewicht"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentRight="true"
    android:layout_below="@+id/numberPicker1"
    android:layout_marginTop="79dp"
    android:text="Gewicht speichern" />

Where´s the problem?

Answer 1

Are you actually populating the number picker with values? As shown below?

NumberPicker np = (NumberPicker) findViewById(R.id.numberPicker1);
String[] nums = new String[20];
for(int i=0; i<nums.length; i++)
       nums[i] = Integer.toString(i);

np.setMinValue(1);
np.setMaxValue(20);
np.setWrapSelectorWheel(false);
np.setDisplayedValues(nums);
np.setValue(1);

Answer 2

the number picker does not have a + or - think of it as more of a scroll wheel. you have to set the minimum number and the maximum number for it to show anything really

setMinValue(5);
setMaxValue(120);

if you click the top portion of the picker it increases the number, if you click the bottom portion of the picker it decreases the number

Answer 3

Make sure that setMinValue and setMaxValue and setValue are being passed the indexes, not the real values. Here is one example, 0-500, skipping by 10:

            NumberPicker number_picker = mRootView.findViewById(R.id.number_picker);
            String[] values = new String[51];
            for (int i = 0; i < values.length; i++) {
                String number = Integer.toString(i * 10);
                values[i] = number;
            }
            number_picker.setMinValue(0);
            number_picker.setMaxValue(50);
            number_picker.setWrapSelectorWheel(false);
            number_picker.setDisplayedValues(values);
            number_picker.setValue(20);

            number_picker.setOnValueChangedListener((picker, oldVal, newVal) ->
                    {
                      //update with newVal
                    }
            );