在Android中以编程方式访问自定义首选项

Question

所以我使用DialogPreference创建了一个自定义首选项 - 没什么特别的;通过XML调用，运行没有任何重大错误：

#posts-wrap {
  padding: 20px;
  text-align: center;
}

ul.medium-grid {
     margin: 0 auto;
    display: inline-block;
    padding: 0;
    text-align: center;
}

#equipment-gallery li {
    float: none;
    list-style: none;
    margin: 20px;
    display: inline-block;
}

当我想以编程方式访问它时出现问题，例如：

public class TimePref extends DialogPreference {

    private TimePicker picker;
    private int value;

    private final static int DEFAULT_VALUE = 0;

    public TimePref(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public TimePref(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected View onCreateDialogView() {
        FrameLayout.LayoutParams layoutParams = new FrameLayout.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
        layoutParams.gravity = Gravity.CENTER;

        picker = new TimePicker(getContext());
        picker.setLayoutParams(layoutParams);

        FrameLayout dialogView = new FrameLayout(getContext());
        dialogView.addView(picker);

        return dialogView;
    }

    @Override
    protected void onBindDialogView(View view) {
        super.onBindDialogView(view);

        picker.setIs24HourView(true);
        setTimePicker(getValue());
    }

    @Override
    protected void onDialogClosed(boolean positiveResult) {
        if (positiveResult) {
            picker.clearFocus();
            int newValue;
            if (Build.VERSION.SDK_INT >= 23 ) {
                newValue = picker.getHour() * 60;
                newValue += picker.getMinute();
            } else {
                newValue = picker.getCurrentHour() * 60;
                newValue += picker.getCurrentMinute();
            }

            if (callChangeListener(newValue)) {
                setValue(newValue);
            }
        }
    }

    @Override
    protected Object onGetDefaultValue(TypedArray a, int index) {
        return a.getInt(index, DEFAULT_VALUE);
    }

    @Override
    protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
        if (restorePersistedValue) {
            if (defaultValue != null)
                setValue((int) defaultValue);
        } else {
            setValue(getPersistedInt(DEFAULT_VALUE));
        }
    }

    public void setValue(int value) {
        this.value = value;
        persistInt(this.value);
    }

    public int getValue() {
        return this.value;
    }

    private void setTimePicker (int value) {
        if (Build.VERSION.SDK_INT >= 23 ) {
            picker.setHour((int) (value / 60));
            picker.setMinute(value % 60);
        } else {
            picker.setCurrentHour((int) (value / 60));
            picker.setCurrentMinute(value % 60);
        }
    }

}

将p返回null并抛出java.lang.NullPointerException。所以问题是，如果你无法“找到”它，如何以编程方式访问自定义首选项？