Initial value is blank when using formatter about numberpicker HOT 4 CLOSED

for ( ... ) {
            
            (snip)

            mNumberPickers[i].setDescendantFocusability(ViewGroup.FOCUS_BLOCK_DESCENDANTS);
            mNumberPickers[i].setFormatter(mStepFormatter);

            mNumberPickers[i].setMinValue(1);
            mNumberPickers[i].setMaxValue(maxValue);
            mNumberPickers[i].setValue((int) Math.floor(level / 5));

            mNumberPickers[i].setVisibility(View.VISIBLE);
            mNumberPickers[i].setWrapSelectorWheel(false);
            mNumberPickers[i].invalidate();
           
            mNumberPickers[i].setOnValueChangedListener( new NumberPicker.OnValueChangeListener() {
                private int colourIndex;
                @Override
                public void onValueChange(NumberPicker picker, int oldVal, int newVal) {
                    mBeaker.getLevels().set(colourIndex, newVal*5);
                    mBeaker.invalidate();
                    invalidateUI();
                }
                public NumberPicker.OnValueChangeListener init(int i) {
                    colourIndex = i;
                    return this;
                }
            }.init(i));

            i++;
        }

int length = 10;
int level = 5;
String[] numbers = new String[length];
for (int i = 0; i < numbers.length; i++) {
    numbers[i] = String.valueOf((i + 1) * level);
}
numberPicker.setMinValue(1);
numberPicker.setMaxValue(length);
numberPicker.setDisplayedValues(numbers);
numberPicker.setValue(5);