prevent user entering text or symbol in a!textdield

This is because the data type is float in a floatingPointField(). The float data type stores an approximate value not an exact value. You will have to use a text field and put some manipulation on the save!value.

One thing you can simply do is the following :

using the validations and the refreshAfter, for example like this here you can get all kind of validations you want. 

a!textField(
    label: "first name " & fv!index,
    value: fv!item.firstName,
    saveInto: fv!item.firstName,
    required: true,
    refreshAfter:"KEYPRESS",
    validations:{
      if (len(fv!item.firstName) < 3, "Please enter more",null)
    }
  ),

I  like using the regex to do Complex Validations . Please find an example how to implement the validation, I personally don't like the option to blank the field to the user if it is not correct, because it can be just 1 characters from a long value, 

=load(
  local!regexDecimal:"^[\$]?[\u0020]?[+-]?([0-9]*[.])?[0-9]+$",

   local!testrows: {
      { data1: "11.0", data2: "$ 1.0" , data3: "$ 1.0"},
      { data1: "11.0", data2: "$ 1.0" , data3: "$ 1.0"},
      { data1: "1.a", data2: "$ 1.a" , data3: "$ 1.a"},
  },
  a!formLayout(
    label: "SAIL Example: Add,Update, or Remove Employee Data",
    contents: {
      a!gridLayout(
        totalCount: count(local!testrows),
        headerCells: {
          a!gridLayoutHeaderCell(label: "Validate1" ),
          a!gridLayoutHeaderCell(label: "Validate2" ),
          a!gridLayoutHeaderCell(label: "Validate3")
        },
        columnConfigs: {
          a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight:3 ),
          a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight:3 ),
          a!gridLayoutColumnConfig(width: "DISTRIBUTE", weight:3 )
        },

        rows: a!forEach(
          items: local!testrows,
          expression: a!gridRowLayout(
            contents: {
              a!textField(
                label: "validate1 " & fv!index,
                value: fv!item.data1,
                saveInto: fv!item.data1,
                required: true,
                refreshAfter:"KEYPRESS",
                validations:{
                  if (len(fv!item.data1) < 4, "Please enter more than 4 characters ",null)
                }
              ),
              a!textField(
                label: "validate2 " & fv!index,
                value:  fv!item.data2,
                saveInto: fv!item.data2,
                required:true,
                refreshAfter:"KEYPRESS",
                validations:{
                 
                  if (regexmatch(local!regexDecimal,fv!item.data2),null,"Please enter valid decimal value with/without $ ")
                }
              ),

              a!textField(
                label: "validate3 " & fv!index,
                value:  if (regexmatch(local!regexDecimal,fv!item.data3),fv!item.data3,null),
                saveInto: fv!item.data3,
                required:true,
                refreshAfter:"KEYPRESS",
                validations:{
                  if (regexmatch(local!regexDecimal,fv!item.data3),null,"Please enter valid decimal value with/without $")
                }
              )
            },
            id: fv!index
          )
        )
      )
    },
    buttons: a!buttonLayout(
      primaryButtons: a!buttonWidgetSubmit(
        label: "Submit"
      )
    )
  )
)

Hope this helps

Note: The regex ins a plugin you can find in the shared components. 

Error Evaluating UI Expression
Expression evaluation error in rule 'eds_showitemroweach' (called by rule 'eds_initiaterbepaymentreview') at function a!applyComponents [line 188]: A null parameter has been passed as parameter 1.

Thanks i removed the extra save and changed to floating point field . still when i type any text , it is giving this error

=a!gridRowLayout(
        Id: ri!index,

        contents: {
           a!textField(
            value: if(rule!APN_isBlank(ri!items[ri!index].sacId), "",ri!items[ri!index].Id ),
             readonly:true()
          ),
          a!textField(
            value: if(rule!APN_isBlank(ri!items[ri!index].sacName), "", ri!items[ri!index].Name),
             readonly:true()
          ),
           a!textField(
            value:if(rule!APN_isBlank(ri!items[ri!index].sacStatus), "",ri!items[ri!index].Status),
            readonly:true()
          ),
          
          a!textField(
            value: if(isnull(ri!items[ri!index].lastMonDis),"",dollar(todecimal(ri!items[ri!index].lastMonDis))),
            readonly:true()
          ),
           a!textField(
            value: if(todecimal(ri!items[ri!index].currentMonDis)=0,"",dollar(ri!items[ri!index].currentMonDis)),
          saveInto:{
              ri!items[ri!index].currentMonDis,
             a!save(ri!itemstoken,append(ri!itemstoken,save!value)),
              a!save(ri!items[ri!index].changeOrdiff,todecimal(ri!items[ri!index].currentMonDis)-todecimal(ri!items[ri!index].lastMonDis)),
               a!save(ri!itemstoken,append(ri!itemstoken,todecimal(ri!items[ri!index].currentMonDis)-todecimal(ri!items[ri!index].lastMonDis)))
            }
           
          ),
           a!textField(
            value: if(todecimal(ri!items[ri!index].currentMonDis)=0,"",dollar(todecimal(ri!items[ri!index].currentMonDis)-todecimal(ri!items[ri!index].lastMonDis))),
            saveInto:{
              ri!items[ri!index].changeOrdiff,
               a!save(ri!itemstoken,append(ri!itemstoken,save!value))
            },
             readonly:true()
          ),
           a!textField(
            value: if(isnull(ri!items[ri!index].currentMonHld),"",dollar(ri!items[ri!index].currentMonHld)),
             readonly:true()
            
          ),
           a!textField(
            value: if(todecimal(ri!items[ri!index].accHldAmount)=0,"",dollar(ri!items[ri!index].accHldAmount)),
              saveInto:{
              ri!items[ri!index].accHldAmount,
             a!save(ri!itemstoken,tostring(append(ri!itemstoken,save!value)))
            }
          ),
           a!textField(
            value: if(rule!APN_isBlank(ri!items[ri!index].reason), "", ri!items[ri!index].reason),
            saveInto:{
              ri!items[ri!index].reason,
              a!save(ri!itemstoken,append(ri!itemstoken,save!value))
            }
          ),
     
        })

Hi, Jamal , Please find the code snippet