如何在Java ME中验证TextField中的输入值

Question

I am writing a simple SRMS, and I need to validate the input from the user if it matches some criteria depending on the field, eg an email field or a phone field. The app is to run in a featured phone and so I am using the Java ME SDK with a virtual machine for testing.

What is the best way to do so, what would be the best way to validate the input and if the input does not meet some criteria, should the user be notified or the value she has entered to be set to null again.

public void name() {
    boolean nameValid = false;
    display = Display.getDisplay(this);
    nameForm = new Form("Student Record Management (1/4");
    TextField firstName = new TextField("First Name(s)", "", 20, TextField.ANY);
    TextField lastName = new TextField("Last Name", "", 20, TextField.ANY);
    TextField personNumber = new TextField("Person Number", "", 10, TextField.NUMERIC);
    back = new Command("BACK", Command.BACK, 1);
    next = new Command("Continue", Command.ITEM, 2);

    nameForm.append(firstName);
    nameForm.append(lastName);
    nameForm.append(personNumber);
    nameForm.addCommand(back);
    nameForm.addCommand(next);
    nameForm.setItemStateListener(this);
    nameForm.setCommandListener(this);
    display.setCurrent(nameForm);

    if (firstName.toString().length() > 0) {
        nameValid = true;
    }
}

The person who started the code has implemented the CommandListener and ItestStateListener .

I am not sure what is the second one does and it has an abstract method to be filled which is called itemStateChanged(Item item) am I supposed to check for changes and validate in here ?

Answer 1

public static boolean validateEmailID(String email) {
email = email.trim();
String reverse = new StringBuffer(email).reverse().toString();
if (email == null || email.length() == 0 || email.indexOf("@") == -1) {
    return false;
}
int emailLength = email.length();
int atPosition = email.indexOf("@");
int atDot = reverse.indexOf(".");

String beforeAt = email.substring(0, atPosition);
String afterAt = email.substring(atPosition + 1, emailLength);

if (beforeAt.length() == 0 || afterAt.length() == 0) {
    return false;
}
for (int i = 0; email.length() - 1 > i; i++) {
    char i1 = email.charAt(i);
    char i2 = email.charAt(i + 1);
    if (i1 == '.' && i2 == '.') {
        return false;
    }
}
if (email.charAt(atPosition - 1) == '.' || email.charAt(0) == '.' || email.charAt(atPosition + 1) == '.' || afterAt.indexOf("@") != -1 || atDot < 2) {
    return false;
}

return true;

}

Answer 2

The ItemStateListener notifies the application of changes in Form items. The item itemStateChanged(Item item) method is called when an item in your form is changed by the user or when Item.notifyStateChanged() is called in an Item. The argument is the Item (Textfield, DateField, ect) that changed value.

I would recommend that you call your validation method inside both the CommandAction and ItemStateListener. In the itemStateChanged only the current Item (the one received in the argument) should be checked. In the CommandAction every field should be checked. This way every Item is validated in every situation.