This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 1 year ago.
I'm working on a program in c# in which I've got an array of objects of a class. I've got a constructor in the class that should give the attached string a value of "" to make sure they're empty so information can be passed in easily. I then have the array created like so:
participants[8][8] grid = new participants[8][];
But I'm being thrown a NullReferenceExcetption error. Here is my code for your reference.
using System;
namespace TreasurehuntCsharp
{
class square
{
public string strX = "";
public int y = 0;
public int x = 0;
}
class participants
{
public string name = "";
public string contact = "";
public participants()
{
name = "";
contact = "";
}
}
class Program
{
//Method for user to choose a square
static void Input(square Coord)
{
//Variables
bool correct = false;
//Inputs
Console.WriteLine("Please enter the coordinates of the square you would like to select: \r\n");
do
{
//X coordinate
Console.WriteLine("X: ");
Coord.strX = Console.ReadLine().ToLower();
//Convert letter to array coordinate
switch (Coord.strX)
{
case "a":
Coord.x = 0;
correct = true;
break;
case "b":
Coord.x = 1;
correct = true;
break;
case "c":
Coord.x = 2;
correct = true;
break;
case "d":
Coord.x = 3;
correct = true;
break;
case "e":
Coord.x = 4;
correct = true;
break;
case "f":
Coord.x = 5;
correct = true;
break;
case "g":
Coord.x = 6;
correct = true;
break;
case "h":
Coord.x = 7;
correct = true;
break;
default:
Console.WriteLine("Please enter a letter from A to H");
correct = false;
break;
}
} while (correct != true);
correct = false;
do
{
//Y coordinate
Console.WriteLine("Y: ");
Coord.y = Convert.ToInt32(Console.ReadLine());
if (Coord.y >= 1 && Coord.y <= 7)
{
correct = true;
}
else
{
Console.WriteLine("Please input an integer value from 1 to 7.");
correct = false;
}
} while (correct != true);
}
static void ParticipantDetails(participants User)
{
Console.WriteLine("Please input your name and Contact number: ");
//User name input
Console.WriteLine("Name: ");
User.name = Console.ReadLine();
//User contact number input
Console.WriteLine("Number: ");
User.contact = Console.ReadLine();
}
static void Main(string[] args)
{
//Objects
square Coord = new square();
participants User = new participants();
//Initialise 2D array
participants[][] grid = new participants[8][];
//Variables
bool correct = false;
do
{
//Methods
Input(Coord);
ParticipantDetails(User);
//Input data to array
if (grid[Coord.x][Coord.y].name == "" && grid[Coord.x][Coord.y].contact == "")
{
grid[Coord.x][Coord.y].name = User.name;
grid[Coord.x][Coord.y].contact = User.contact;
Console.WriteLine(grid[Coord.x][Coord.y]);
correct = true;
}
else
{
Console.WriteLine("That square is already filled. Please try again.");
correct = false;
}
} while (correct == false);
}
}
You did not initialize all the dimensions of the array.
//Initialise 2D jagged array
participants[][] grid = new participants[8][];
// You can do that in a for loop
grid[0] = new participants[8];
grid[1] = new participants[8];
grid[2] = new participants[8];
...
grid[7] = new participants[8];
// For loop equivalent
for (int i = 0; i < grid.Length; i++)
{
grid[i] = new participant[8];
}
A better way for your case (since all the sub-arrays have the same number of elements), would be to use multidimensional-arrays
participants[,] grid = new participants[8,8];
// and access like this
grid[Coord.x, Coord.y]
You created an array of arrays.
participants[][] grid = new participants[8][];
It is an array with 8 entries. Each of the entries is supposed to be an array of participants, but it hasn't been created.
What you need to do is to create 8 arrays and assign them to the elements of the grid array.
participant[][] grid = new participant[8][];
for (int i = 0; i < grid.Length; i++)
grid[i] = new participant[8];
Here I assume that each element of the grid array is also going to contain 8 elements, but it's up to you.
Together with a friend, we are trying to create a sea battle for playing on a local network, we made a field of buttons, created islands on it, you can set up ships and move them. But when we connected the form to our server, after requesting the package, the form stops drawing buttons, they store the correct data, but their visual update does not occur
Here are the pieces of code
private void button1_Click(object sender, EventArgs e)
{
comboBox1.Visible = false;
comboBox2.Visible = false;
button1.Visible = false;
comboBox3.Visible = false;
button2.Visible = true;
SendPacket(PacketInfo.SendGameInfo);
Thread thread = new Thread(FightIsDone);
thread.Start();
State = GameState.Waiting;
}
void FightIsDone()
{
ReceivePacket();
this.Invoke(new Action(() => GameUpdate()));
}
public void GameUpdate()
{
Console.WriteLine("!");
State = GameState.Planing;
foreach (Ship ship in Ships)
{
ship.UseModuls();
}
SetShip(Ships);
UpdateSight();
Draw();
}
The problem is here, this method changes the image of the button or its color, it works fine until the packet is sent to the server, but after receiving it, only the information is updated, and the appearance of the form does not change
public void Draw()
{
foreach (CellButton Butt in Field)
{
if (Butt.Sigth)
{
Butt.Image = null;
SetImage(Butt);
}
else
{
Butt.BackColor = Color.Gray;
Butt.Image = null;
}
}
}
public void SetImage(CellButton Butt)
{
switch (Butt.Entety)
{
case GameObject.Water: Butt.BackColor = Color.DodgerBlue; break;
case GameObject.Island: Butt.Image = GetObjectImage(GameObject.Island); break;
case GameObject.Ship:
{
Butt.Image = Butt.modul.ModulImage;
break;
}
case GameObject.Torpedo: Butt.BackColor = Color.DarkBlue; break;
case GameObject.Fire: Butt.Image = GetObjectImage(GameObject.Fire); break;
}
}
static void SendPacket(PacketInfo info)
{
ms.Position = 0;
switch (info)
{
case PacketInfo.Connect:
writer.Write(0);
break;
case PacketInfo.SendCoordinate:
writer.Write(1);
formatter.Serialize(ms, new Coordinate(5, 0));
break;
case PacketInfo.LaunchSearch:
writer.Write(2);
writer.Write(Me.ID);
break;
case PacketInfo.SendGameInfo:
writer.Write(3);
writer.Write(Me.ID);
List<Ship> shpooks = new List<Ship>();
foreach (Ship s in Ships)
if (s.PlayerID == Me.ID) shpooks.Add(s);
formatter.Serialize(ms, shpooks);
break;
}
socket.Send(ms.GetBuffer());
}
static int ReceivePacket()
{
ms.Position = 0;
socket.Receive(ms.GetBuffer());
int code = reader.ReadInt32();
switch (code)
{
case 0:
{
Console.WriteLine("Catch");
Console.WriteLine(ms.ToString());
bool IsConected = reader.ReadBoolean();
if (IsConected)
{
Me.ID = reader.ReadInt32();
return 1;
}
break;
}
case 2:
{
return 1;
break;
}
case 3:
{
Cell[,] cells = (Cell[,])formatter.Deserialize(ms);
for (int i = 0; i < Width; i++)
for (int j = 0; j < Hight; j++)
{
Field[i, j] = new CellButton(new Coordinate(i, j));
Field[i, j].SetCell(cells[i, j]);
}
Ships.Clear();
Ships.AddRange((List<Ship>)formatter.Deserialize(ms));
break;
}
}
return -1;
}
This is the form before calling Draw():
This is how the form looks after calling Draw():
And so, after a request to the server and method Draw():
I spent a lot of time finding solutions, methods like Form.Update() and Form.Refresh() don't help
I was wondering how I would make a picture box become invisible or visible when a certain integer matches.
My program revolves around 2 players going around a board, and when they add there 2 Di up, they will move the amount of spaces.
My problem being, My friend and I have no idea what is wrong with the current code we have, it throws no errors which baffles him, especially myself.
I've made it so my program add's the Di up on every roll, and add's it to the integer.
Anyone have any idea's on whats wrong? If not, a better approach?
Code
private void SelectPos(PictureBox pic)
{
PictureBox[] numbers = { P1_1, P1_2, P1_3, P1_4, P1_5, P1_6, P1_7, P1_8, P1_9, P1_10, P1_11, P1_12, P1_13, P1_14, P1_15, P1_16, P1_17, P1_18, P1_19, P1_20, P1_21, P1_22, P1_23, P1_24, P1_25, P1_26, P1_27, P1_28, P1_29, P1_30, P1_31, P1_32, P1_33, P1_34, P1_35, P1_36, P1_37, P1_38, P1_39, P1_40, P1_41, P1_42, P1_43, P1_44, P1_45, P1_46, P1_47, P1_48, P1_49 };
for (int i = 0; i < numbers.Length; i++)
{
if (pic == numbers[i])
{
numbers[i].Visible = true;
MessageBox.Show("k");
}
{
numbers[i].Visible = false;
MessageBox.Show("l");
}
}
}
private void bunifuFlatButton1_Click(object sender, EventArgs e)
{
Roll();
System.Threading.Thread.Sleep(100);
Roll2();
Goes_Num.Text = (int.Parse(Goes_Num.Text) + 1).ToString();
if (Convert.ToInt32(Goes_Num.Text) % 2 == 0)
{
WhichPlayer.Text = "Player 2";
P2_Number.Text = (int.Parse(P2_Number.Text) + 1).ToString();
int p2Int = Convert.ToInt32(P2_Pos.Text);
P2_Pos.Text = (p2Int + dice + dice2).ToString();
}
else if (Convert.ToInt32(Goes_Num.Text) % 2 != 0)
{
WhichPlayer.Text = "Player 1";
P1_Number.Text = (int.Parse(P1_Number.Text) + 1).ToString();
int p1Int = Convert.ToInt32(P1_Pos.Text);
P1_Pos.Text = (p1Int + dice + dice2).ToString();
int P1 = (Convert.ToInt32(P1_Pos.Text));
SelectPos(P1_1);
/*switch (P1)
{
case 1:
P1_1.Visible = true;
break;
case 2:
P1_2.Visible = true;
break;
}*/
/*String[] hi = { "1", "2" };
for (int i = 0; i < hi.Length; i++)
{
var visible = p1
if(visible == hi[i])
{
hi[i].Visible = true;
}
else
{
hi[i].Visible = false;
}
}*/
}
}
(P1-1 all the way to P1-49 are images)
Thanks,
James
It looks like you're trying to pass an int to your SelectPos function but it expects a PictureBox. You could fix this doing something similar to the following:
private void SelectPos(int pic)
{
PictureBox[] numbers = { P1_1, P1_2, P1_3, P1_4, P1_5, P1_6, P1_7, P1_8, P1_9, P1_10, P1_11, P1_12, P1_13, P1_14, P1_15, P1_16, P1_17, P1_18, P1_19, P1_20, P1_21, P1_22, P1_23, P1_24, P1_25, P1_26, P1_27, P1_28, P1_29, P1_30, P1_31, P1_32, P1_33, P1_34, P1_35, P1_36, P1_37, P1_38, P1_39, P1_40, P1_41, P1_42, P1_43, P1_44, P1_45, P1_46, P1_47, P1_48, P1_49 };
//Set all picture boxes to be not visible
for (int i = 0; i < numbers.Length; i++)
{
numbers[i].Visible = false;
}
//Set the picture at the given index to visible
numbers[pic].Visible = true;
}
private void bunifuFlatButton1_Click(object sender, EventArgs e)
{
Roll();
System.Threading.Thread.Sleep(100);
Roll2();
Goes_Num.Text = (int.Parse(Goes_Num.Text) + 1).ToString();
if (Convert.ToInt32(Goes_Num.Text) % 2 == 0)
{
WhichPlayer.Text = "Player 2";
P2_Number.Text = (int.Parse(P2_Number.Text) + 1).ToString();
int p2Int = Convert.ToInt32(P2_Pos.Text);
P2_Pos.Text = (p2Int + dice + dice2).ToString();
}
else if (Convert.ToInt32(Goes_Num.Text) % 2 != 0)
{
WhichPlayer.Text = "Player 1";
P1_Number.Text = (int.Parse(P1_Number.Text) + 1).ToString();
int p1Int = Convert.ToInt32(P1_Pos.Text);
P1_Pos.Text = (p1Int + dice + dice2).ToString();
int P1 = (Convert.ToInt32(P1_Pos.Text));
SelectPos(P1);
}
}
You may have to manipulate the value of pic so that it is within the bounds of the array (0-48). For example if pic is between 1 and 49 you would need to subtract 1: numbers[pic-1]. Without seeing your whole program I can't tell you exactly how that part of the code would look but it should be pretty easy to figure out. If you aren't familiar with arrays and indexing check out this link or just Google C# Arrays.
As a side note it would be better to the numbers array as a private member of the class this code is in. Unless the values in the array change there's no point in building the array every time the method is called.
Complete code:
private void SelectPos(int pic)
{
PictureBox[] numbers = { P1_1, P1_2, P1_3, P1_4, P1_5, P1_6, P1_7, P1_8, P1_9, P1_10, P1_11, P1_12, P1_13, P1_14, P1_15, P1_16, P1_17, P1_18, P1_19, P1_20, P1_21, P1_22, P1_23, P1_24, P1_25, P1_26, P1_27, P1_28, P1_29, P1_30, P1_31, P1_32, P1_33, P1_34, P1_35, P1_36, P1_37, P1_38, P1_39, P1_40, P1_41, P1_42, P1_43, P1_44, P1_45, P1_46, P1_47, P1_48, P1_49 };
//Set all picture boxes to be not visible
for (int i = 0; i < numbers.Length; i++)
{
numbers[i].Visible = false;
}
//Set the picture at the given index to visible
numbers[pic].Visible = true;
}
private void SelectPos2(int pic2)
{
PictureBox[] numbers2 = { P2_1, P2_2, P2_3, P2_4, P2_5, P2_6, P2_7, P2_8, P2_9, P2_10, P2_11, P2_12, P2_13, P2_14, P2_15, P2_16, P2_17, P2_18, P2_19, P2_20, P2_21, P2_22, P2_23, P2_24, P2_25, P2_26, P2_27, P2_28, P2_29, P2_30, P2_31, P2_32, P2_33, P2_34, P2_35, P2_36, P2_37, P2_38, P2_39, P2_40, P2_41, P2_42, P2_43, P2_44, P2_45, P2_46, P2_47, P2_48, P2_49 };
//Set all picture boxes to be not visible
for (int i = 0; i < numbers2.Length; i++)
{
numbers2[i].Visible = false;
}
//Set the picture at the given index to visible
numbers2[pic2].Visible = true;
}
private void bunifuFlatButton1_Click(object sender, EventArgs e)
{
Roll();
System.Threading.Thread.Sleep(100);
Roll2();
Goes_Num.Text = (int.Parse(Goes_Num.Text) + 1).ToString();
if (Convert.ToInt32(Goes_Num.Text) % 2 == 0)
{
WhichPlayer.Text = "Player 2";
P2_Number.Text = (int.Parse(P2_Number.Text) + 1).ToString();
int p2Int = Convert.ToInt32(P2_Pos.Text);
P2_Pos.Text = (p2Int + dice + dice2).ToString();
int P2 = (Convert.ToInt32(P2_Pos.Text));
SelectPos2(P2);
}
else if (Convert.ToInt32(Goes_Num.Text) % 2 != 0)
{
WhichPlayer.Text = "Player 1";
P1_Number.Text = (int.Parse(P1_Number.Text) + 1).ToString();
int p1Int = Convert.ToInt32(P1_Pos.Text);
P1_Pos.Text = (p1Int + dice + dice2).ToString();
int P1 = (Convert.ToInt32(P1_Pos.Text));
SelectPos(P1);
}
}
I have a menustrip consists of Menu and Tools
in "Menu" i have subMenus like msO1,msO2,msO3......., and on "Tools" i have subMenus like msP1,msP2,msP3.......,
on Form load all the subMenus visible is false..., On button Click user want to select which subMenus he want...,
in the textBox(txtSelect) if user enter 1,3..., he get msO1, msO3.....,
my code is a hardcode..., if i have 20 subMenus means this code is not helpfull anybody have an idea...,
private void btnSelect_Click_1(object sender, EventArgs e)
{
msO1.Visible = false;//msO1 is a submenu
msO2.Visible = false;
msO3.Visible = false;
msP1.Visible = false;
msP2.Visible = false;
msP3.Visible = false;
string word = txtSelect.Text;
string[] splt = word.Split(',');
int[] arrayItms = new int[splt.Length];
for (int x = 0; x < splt.Length; x++)
{
arrayItms[x]=Convert.ToInt32(splt[x].ToString());
if (splt.Length > 0)
{
switch (arrayItms[x])
{
case 1:
msO1.Visible = true; break;
case 2:
msO2.Visible = true; break;
case 3:
msO3.Visible = true; break;
case 4:
msP1.Visible = true; break;
case 5:
msP2.Visible = true; break;
case 6:
msP3.Visible = true; break;
}
}
}
}
Create an array of your MenuStrip
MenuStrip[] mstrip = new MenuStrip[]
{
msO1,msO2, msO3, msP1, msP2, msP3 // add other menus here when needed
};
now you could work on the array as a Whole to make visible or not your menus
for(int x = 0; x < menus.Length; x++)
mstrip[x].Visible = false;
and your code could be simplified with
for (int x = 0; x < splt.Length; x++)
{
int menuIndex;
if(Int32.TryParse(splt[x], out menuIndex))
{
menuIndex--;
if(menuIndex >= 0 && menuIndex < mstrip.Length)
mstrip[menuIndex].Visible = true;
}
}
Remember, arrays indexes start at zero (while your user will probably start counting a 1).
You could use something like this
string word = txtSelect.Text;
string[] splt = word.Split(',');
for (int x = 0; x < splt.Length; x++)
{
Control myControl1 = FindControl("ms" + splt[x]);
if ( myControl1 != null )
(ToolStripMenuItem)myControl1.Visible = true;
}
Untested but this should get you half way there I hope.
Loop through each ToolStripMenuItem control in the menu strip items and set them to visible.
You can add further conditions inside the loop to define which of the menu items should be made visible based on the users choice..
foreach (ToolStripMenuItem mi in menuStrip1.Items)
{
mi.Visible = true;
}
I'm geting a StackOverflowException. Somehow, posting here seemed appropriate.
I'm using Windows Forms in a C# application. This application is intended to run on Linux, FreeBSD and Mac-OS, so I can't use WPF, so please don't suggest it.
My guess is that I'm missing a nuance of WinForms, but I cant seem to figure out what.
The ComboBox is generated by the GUI form builder in VS 2010.
The specific lines of code that are throwing the error are here:
if(cur_num_is_valid)
{
cbx_material_num.Text = num;
}
else
{
num = "0";
//I only have one of the following two at a time. Both overflow
cbx_material_num.SelectedIndex = 0;
cbx_material_num.Text = "0";
}
Since the code is somewhat complex, here's the whole function code. 'cbx_' indicates a combo box. 'txtb_' is a text box.
private void cbx_material_numobj_SelectedIndexChanged(object sender, EventArgs e)
{
string obj = cbx_material_obj.Text;
string num = cbx_material_num.Text;
int selnum = 0;
int n = 0;
//do we need to recreate the numbers array?
bool cur_num_is_valid = false;
cbx_material_num.Items.Clear();
if(obj != lastobj)
{
n = m_demo.get_object_modifiers(obj);
for(int i = 0; i <= n; i++)
{
string s = i.ToString();
if(s == num && i < n) cur_num_is_valid = true;
cbx_material_num.Items.Add(s);
}
}
if(cur_num_is_valid)
{
cbx_material_num.Text = num;
}
else
{
num = "0";
//Overflow here:
cbx_material_num.SelectedIndex = 0;
}
try
{
selnum = int.Parse(num);
}
catch(Exception)
{
MessageBox.Show("Error, second select menu after 'object modifiers' must be a number, not '"+num+"'.");
cbx_material_num.Text="0";
return;
}
if(selnum >= n)
{
txtb_material_param1.Text = "0";
txtb_material_param2.Text = "0";
txtb_material_param3.Text = "0";
txtb_material_param4.Text = "0";
}
else
{
MaterialFace face;
MaterialParameter parameter;
int typeid;
object paramdata;
m_demo.get_object_modifiers_material(obj, selnum, out face, out parameter, out typeid, out paramdata);
cbx_material_face.Text = face.ToString();
cbx_material_paramtype.Text = parameter.ToString();
switch(typeid)
{
case 0:
txtb_material_param1.Text = ((float)paramdata).ToString();
cbx_material_datatype.Text = "float";
goto case -1;
case 1:
float[] parsf = ((float[])paramdata);
txtb_material_param1.Text = parsf[0].ToString();
txtb_material_param2.Text = parsf[1].ToString();
txtb_material_param3.Text = parsf[2].ToString();
txtb_material_param4.Text = parsf[3].ToString();
cbx_material_datatype.Text = "float[]";
break;
case 2:
txtb_material_param1.Text = ((int)paramdata).ToString();
cbx_material_datatype.Text = "int";
goto case -1;
case 3:
int[] parsi = ((int[])paramdata);
txtb_material_param1.Text = parsi[0].ToString();
txtb_material_param2.Text = parsi[1].ToString();
txtb_material_param3.Text = parsi[2].ToString();
txtb_material_param4.Text = parsi[3].ToString();
cbx_material_datatype.Text = "int[]";
break;
case -1: //can't actuall be returned, used to 'blank' the last three as '0'
txtb_material_param2.Text = "0";
txtb_material_param2.Text = "0";
txtb_material_param3.Text = "0";
break;
case 4:
OpenTK.Graphics.Color4 paramc = ((OpenTK.Graphics.Color4)paramdata);
txtb_material_param1.Text = paramc.R.ToString();
txtb_material_param2.Text = paramc.G.ToString();
txtb_material_param3.Text = paramc.B.ToString();
txtb_material_param4.Text = paramc.A.ToString();
cbx_material_datatype.Text = "Color4";
break;
default: //5
Vector4 paramv = ((Vector4)paramdata);
txtb_material_param1.Text = paramv.X.ToString();
txtb_material_param2.Text = paramv.Y.ToString();
txtb_material_param3.Text = paramv.Z.ToString();
txtb_material_param4.Text = paramv.W.ToString();
cbx_material_datatype.Text = "Vector4";
break;
}
}
}
You need to check that the SelectedIndex isn't already 0 before you try to set it:
if (cbx_material_num.SelectedIndex != 0){
cbx_material_num.SelectedIndex = 0;
}
Otherwise you're re-firing the event every time through.
I think that whenever you set this cbx_material_num.SelectedIndex = 0; within the EventHandler you invoke your
cbx_material_numobj_SelectedIndexChanged(object sender, EventArgs e)
Each call invokes another eventHandler so the stack fills up after some time.
Basically, the fact that it is called SelectedIndexChanged doesn't mean that the value has to be different from the previous one but that the value is set through its setter.