# Get input for a function in a custom block
**URL:** https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357
**Category:** micro:bit
**Created:** [June 10, 2020, 2:42am UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357 "2020-06-10T02:42:12Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@ameyrr250](https://forum.makecode.com/u/ameyrr250)
#### Post date: [June 10, 2020, 2:42am UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/1 "2020-06-10T02:42:12Z")
Hi,
I have a function inside a custom block and I need to get two inputs for it,
1. a buffer
2. a number from an enum
Right now the way I am trying to get an input is
//%block=“Send buffer $Buf to click $BoardNum” …(This is what I want displayed while accepting inputs as ‘Buf’ and ‘BoardNum’
sendBuffer( Buf: Buffer,BoardNum: BoardID){
The issue that I face with this is that I get an error on the webpage while building the block as "property 'sendBuffer does not exist on type buffer.
If I change the $ to %
//%block=“Send buffer %Buf to click %BoardNum”
I get the error that only one input is given altough two were expected.
Can someone please explain how I could get inputs for functions inside a class from the user in custom blocks?
---
### Author:  [@bsiever](https://forum.makecode.com/u/bsiever)
#### Post date: [June 10, 2020, 1:12pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/2 "2020-06-10T13:12:54Z")
You may want to try testing it out and exploring the examples on the playground: [https://makecode.com/playground](https://makecode.com/playground)
That being said, I think the below works. Note that I’ve put the `enum`s in the `namespace`. I think this may cause problems with some of the “block rendering” tools for documentation. Many other MakeCode examples (including on the playground) have the `enum`s outside the namespace. **If anyone from the MakeCode team could weigh in on best-practices, it’d be appreciated!**
```auto
//% color="#AA278D"
namespace basic {
export class Buffer {
}
export enum BoardId {
One,
Two,
Three,
Four
}
//% block="Send buffer $buf to click $BoardNum"
export function sendBuffer(buf: Buffer, choice: BoardId) {
}
}
```
---
### Author:  [@richard](https://forum.makecode.com/u/richard)
#### Post date: [June 10, 2020, 4:46pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/3 "2020-06-10T16:46:22Z")
Can you paste your entire block definition? If this is a method on a class, you need to also include the `this` parameter in the block definition. You can do that like this:
```auto
//% block="$this send buffer $Buf to click $BoardNum"
//% this.shadow=variables_get
//% this.defl=someName
```
The `shadow` and `defl` comments in this case tell MakeCode to make the `this` parameter a variable with the name “someName”.
You shouldn’t use `%` when defining blocks, it’s the old (deprecated) way of listing parameters. `$` is the new way going forward. We have a lot of blocks inside of makecode that are still defined that way but it’s just because we can’t update them (it would break our existing translations)
---
### Author:  [@bsiever](https://forum.makecode.com/u/bsiever)
#### Post date: [June 10, 2020, 5:00pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/4 "2020-06-10T17:00:48Z")
Can you comment on `enum`s for parameters? Should they be in the namespace and exported or outside the namespace?
It seems like keeping them in the namespace is more in keeping with the intent of using namespaces.
---
### Author:  [@ameyrr250](https://forum.makecode.com/u/ameyrr250)
#### Post date: [June 10, 2020, 5:26pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/5 "2020-06-10T17:26:13Z")
Hi,
Thanks for the reply
This is the class under the namespace (there are multiple classes)
///START of SPISettings
export class SPIsetting{
// SPI Function Ids
protected SPI\_WRITE\_id : number
protected SPI\_READ\_id : number
protected SPI\_CONFIG\_id : number
protected SPI\_WRITEBULK\_id : number
protected SPI\_WRITEBULK\_CS\_id : number
protected SPI\_READBULK\_CS\_id : number
protected SPI\_BAUD\_id : number
protected SPI\_CONFIG\_CS\_id : number
```
constructor(){
this.SPI_WRITE_id = 1
this.SPI_READ_id = 2
this.SPI_CONFIG_id = 3
this.SPI_WRITEBULK_id = 4
this.SPI_WRITEBULK_CS_id = 5
this. SPI_READBULK_CS_id = 6
this.SPI_BAUD_id = 7
this.SPI_CONFIG_CS_id = 8
}
```
//%blockId=send\_UART\_Buffer
//%block=“Send buffer %Buf to click %BoardNum”
//% blockGap=7
//% weight=90 color=#9E4894 icon=“”
//% advanced=false
```
sendBuffer( Buf: Buffer,BoardNum?: BoardID){
let buffLength = Buf.length+4;
let UARTBuf = pins.createBuffer(buffLength);
UARTBuf.setNumber(NumberFormat.UInt8LE, 0, RX_TX_Settings.BBOARD_COMMAND_WRITE_RX_BUFFER_DATA)
UARTBuf.setNumber(NumberFormat.UInt8LE, 1, clickBoardNum)
UARTBuf.setNumber(NumberFormat.UInt8LE, 2, UART_module_id)
UARTBuf.setNumber(NumberFormat.UInt8LE, 3, 5)
for(let i=0; i
### Author:  [@richard](https://forum.makecode.com/u/richard)
#### Post date: [June 10, 2020, 5:39pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/6 "2020-06-10T17:39:52Z")
It’s better to keep this discussion in the thread so that others can find it.
Yep, you need to add the $this to your definition. The “cannot read vtable of undefined” likely means that you are passing a variable that hasn’t been assigned. That’s the makecode equivalent of a null pointer exception.
---
### Author:  [@richard](https://forum.makecode.com/u/richard)
#### Post date: [June 10, 2020, 5:41pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/7 "2020-06-10T17:41:11Z")
For enums, we typically put them outside a namespace to make the code less verbose. It’s really up to the extension author though!
---
### Author:  [@bsiever](https://forum.makecode.com/u/bsiever)
#### Post date: [June 10, 2020, 5:57pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/8 "2020-06-10T17:57:14Z")
Great! Thanks — I’m using some common names for `enum`s, so I’ll keep them in my namespace to avoid collisions as long as it doesn’t matter otherwise.
---
### Author:  [@ameyrr250](https://forum.makecode.com/u/ameyrr250)
#### Post date: [June 10, 2020, 6:18pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/9 "2020-06-10T18:18:12Z")
export class I2CSettings{
```
// I2C Function Ids
protected I2C_WRITE_id : number
protected I2C_READ_id : number
protected I2C_WRITE_NO_MEM_id : number
protected I2C_READ_NO_MEM_id : number
constructor(){
this.I2C_WRITE_id = 1
this.I2C_READ_id = 2
this.I2C_WRITE_NO_MEM_id = 3
this.I2C_READ_NO_MEM_id = 4
}
//%blockId=send_UART_String
//%block="$this Send string $UARTString to click$clickBoardNum"
//% this.shadow=variables_get
//% this.defl=someName
//% blockGap=7
//% weight=90 color=#9E4894 icon=""
//% advanced=false
sendString( UARTString: string,clickBoardNum: clickBoardID){
let remainingBytes = UARTString.length
while( remainingBytes )
{
let messageLength = Math.min(remainingBytes+ 4,128);
let UARTBuf = pins.createBuffer(messageLength);
UARTBuf.setNumber(NumberFormat.UInt8LE, 0, RX_TX_Settings.BBOARD_COMMAND_WRITE_RX_BUFFER_DATA)
UARTBuf.setNumber(NumberFormat.UInt8LE, 1, clickBoardNum)
UARTBuf.setNumber(NumberFormat.UInt8LE, 2, UART_module_id)
UARTBuf.setNumber(NumberFormat.UInt8LE, 3, 5)
for(let i=4; i
### Author:  [@richard](https://forum.makecode.com/u/richard)
#### Post date: [June 10, 2020, 6:24pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/10 "2020-06-10T18:24:43Z")
That looks right! Usually that means that in the program where you’re using this class, you haven’t assigned the variable that’s being passed into `this`
Usually we have a function outside the class that’s called `create ____ `.
like this:
```auto
namespace whatever {
//% block="create i2c settings"
//% blockSetVariable=someName
export function createI2cSettings(): I2CSettings {
return new I2CSettings();
}
}
```
The `blockSetVariable` annotation will make it so that this block is assigned to a variable in the toolbox.
---
### Author:  [@ameyrr250](https://forum.makecode.com/u/ameyrr250)
#### Post date: [June 14, 2020, 7:34pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/11 "2020-06-14T19:34:46Z")
Hi I still get cast errors when using functions from inside the class. I have to keep functions outside the class and create a object using
let i2cobj=new I2CSettings(); and then use these functions.
I know I’m doing something wrong, but can’t igure it out.
This is one example
//\*\*
//\* Provides access to basic micro:bit functionality.
//\*/
//% color=#1E90FF weight=116 icon="\uf00a"
//% advanced=true
namespace Force\_Click{
```
export class Force{
A : number;
sumA : number;
Force_voltage : number;
Force_val : number;
rangefactor : number;
Vadc_3 : number;
constructor(){
this.A=0;
this.sumA=0;
this.Force_voltage=0;
this.Force_val=0;
this.rangefactor=20/3.3
this.Vadc_3=3.3/4096;
}
//%blockId=force
//%block="For $this Get value of force on click$clickBoardNum"
//% blockGap=7
//% this.shadow=variables_get
//% this.defl=forceClick
//% weight=90 color=#9E4894 icon=""
//% advanced=false
forceclick(clickBoardNum: clickBoardID) : number{
for (let i=1;i<=20;i++)
{
this.A=(bBoard.analogRead(clickADCPin.AN,clickBoardNum))
this.sumA+=force.A;
}
this.sumA=force.sumA/20;
this.Force_voltage=this.sumA*this.Vadc_3; //Voltage for the force click board
this.Force_val=this.Force_voltage*this.rangefactor;
return this.Force_val
}
```
}
```
export function createForce(): Force {
return new Force();
```
}
```
let force=new Force();
//%blockId=forceS
//%block="Get string value of force on click$clickBoardNum"
//% blockGap=7
//% weight=100 color=#9E4894 icon=""
//% advanced=false
export function forceclickstring(clickBoardNum: clickBoardID) : string{
let valueForce= force.forceclick(clickBoardNum);
let stringForce= valueForce.toString();
return stringForce;
}
```
}
I have tried one function from inside the class and one from outside, if i put the function inside the class, I get cast errors
---
### Author:  [@ameyrr250](https://forum.makecode.com/u/ameyrr250)
#### Post date: [June 30, 2020, 12:13pm UTC](https://forum.makecode.com/t/get-input-for-a-function-in-a-custom-block/2357/12 "2020-06-30T12:13:09Z")
Hi,
I want to have all my functions in a class for each main block. Right now what I do is,
namespace ABC{
//% block=“create lcd settings”
//% blockSetVariable=“ABCObjSettings”
//% weight=110
export function createABCObjSettings(): ABCObjSettings{
return new ABCObjSettings();
}
export class ABC{
…
…
…
//% block="$this example $variablePassed
//% blockId=Example
//% blockNamespace=ABC
//% this.shadow=variables\_get
//% this.defl=“ABCObjSettings”
//% weight=90
exampleExposedFunction(variablePassed : number) {
sum=this.variablePassed
}
}
}
In the blocks on the webpage, I have to first place the “set ABCObjSettings to create lcd settings”, then select my exposed function.
I have to place the “set ABCObjSettings to create lcd settings” at least once to use any exposed
Is there a way to automatically create that Object and use?
Thanks!