getText() from EditText: is it possible to get a 'null'?

Question

I'm working through an Android app I'm writing and attempting to bring my code fully in line with Android Studio's lint recommendations.

I have the following code that is issuing a warning (some code is omitted):

final EditText input = (EditText)view.findViewById(R.id.edit_text);
Button button        = (Button)view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        String value = input.getText().toString();
        if (value == null || value.length() == 0) {

Android Studio is giving me a warning that:

Condition 'value == null' is always false.

When I allow Android Studio to "fix" the problem for me, it recommends:

Simplify 'value == null' to false

The code then becomes:

if (value.length() == 0) {

I've looked through the Android source code (http://www.grepcode.com) and I'm confused. The documentation for EditText says "EditText is a thin veneer over TextView that configures itself to be editable." Then, the getText() method is defined as follows:

@Override
public Editable getText() {
    return (Editable) super.getText();
}

When I go to getText() for a TextView (the "super"), I see this:

public CharSequence getText() {
    return mText;
}

The setText() method for a TextView appears to disallow a null value, because this is the start of that method:

private void setText(CharSequence text, BufferType type, boolean notifyBefore, int oldlen) {
    if (text == null) {
        text = "";
    }

The default constructor starts this way, too:

public TextView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    mText = "";

So, it would appear that there is no way for getText() to return a null value, but the comments on this answer indicate that it is. The answers to this question also seem to indicate that it is possible.

I'd like to practice defensive coding, which is why I structured my code the way I did from the beginning, but I don't want to be doing a null check for something that cannot possibly be null. So, what's the best practice in this case?

Answer 1

I think the lint check is telling you something slightly differently:

String value = input.getText().toString();
if (value == null || value.length() == 0) {

Condition 'value == null' is always false.

It actually doesn't matter in this if-statement whether or not EditText.getText() can ever return null. Because if it returns null, then the .toString() will have caused a NullPointerException before the if-statement is even reached. Therefore, if the if-statement is at all reachable, value cannot be null.

You can dig all through the Android source code, and maybe you will find that there's no possible way for EditText to return null. If that is the case, then you can just ignore the lint warning if you know that the standard EditText is in your app.

However, in the more general case, nothing is stopping me from sticking this in the view hierarchy:

public class EvilEditText extends EditText {
    // Constructors

    @Override
    public Editable getText() {
        return null;
    }
}

so the safest option is to rewrite your code to be completely nullsafe:

Editable e = input.getText();
String value = (e == null ? null : e.toString());
if (TextUtils.isEmpty(value)) {  //hat tip to Deepak Goyal's answer. Could also use isEmpty(e)

Answer 2

You can use TextUtils.isEmpty(value);

final EditText input = (EditText)view.findViewById(R.id.edit_text);
Button button        = (Button)view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        String value = input.getText().toString();
        if (TextUtils.isEmpty(value)) {
          // value is empty
        }else{
          // have value
        }

Answer 3

You are likely receiving this warning because your value does not hold what is returned from EditText#getText() (which returns a CharSequence), it instead holds the return from CharSequence#toString() (which returns a String).

It should be impossible for a toString() call on a non-null CharSequence to return null, this is why lint warns you that the null check is unnecessary. You should do the null check on the return of EditText#getText() instead.

In other words, if your input.getText() was null, it would already fail without getting to call toString(), hence your null check would never be reached.

Answer 4

The value in the expression

String value = input.getText().toString();

will not be null. Since if input is null it will generetae an NPE for the method call input.getText(). and hence the next statement won't execute. If you handles this NPE somthing like

            String value = null;
            if (input!=null) {
                value = input.getText().toString();
            }
            if (value == null || value.length() == 0){

            }

Then you won't get that Indication.