Preferences table Null Pointer Exception

[L1TH1UM]

Hello,

We are having some issues using the preferences table utility on SmartDashboard. We are supposed to be getting a table from which we can edit robot preferences such as potentiometer setpoints and encoder setpoints.

However, when we run the code it throws a Null Pointer Exception because we declared the preferences varable (Preferences prefs;) but we didn't create and object and we are trying to use an operator (prefs.getDouble). Using "prefs = new Preferences();" does not work, and there's nothing on the wpilibj documentation that tells us how to fix this (create an object for preferences).

Here's the page we're referencing: https://wpilib.screenstepslive.com/s/4485/m/26401/l/255423-setting-robot-preferences-from-smartdashboard

Our code is almost exactly the same as that just minor differences such as names and values. We are programming in Java.

Any help would be appreciated, thanks.

[RufflesRidge]

The sample on that page seems to be missing a line:

prefs = Preferences.getInstance();

[Arhowk]

The sample on that page seems to be missing a line:

prefs = Preferences.getInstance();

You're right! Thats quite funny. Here's the actual code for reference

package org.usfirst.frc.team40.robot;

import edu.wpi.first.wpilibj.SampleRobot;
import edu.wpi.first.wpilibj.Preferences;

public class Robot extends SampleRobot{

Preferences prefs;
double armUpPosition;
double armDownPosition;
public void robotInit(){
prefs = Preferences.getInstance();
armUpPosition = prefs.getDouble("ArmUpPosition", 1.0);
armDownPosition = prefs.getDouble("ArmDownPosition", 4.0);
}
}



On a side note, to follow NetworkTable conventions the method name should be "getNumber" but that is trivial.

[L1TH1UM]

Thank you, I appreciate it. This fixed our problem.

[MrRoboSteve]

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