Question

I’m a beginner in Android development. In my project, I created a TableLayout –I reckon that a GridLayout can do more help, but since I’m not familiar with GridLayout TableLayout was taken — with some EditTexts to get values from user. The activity actually is a submit-able form. To left of each EditText, there is a TextView defining what is expected from the corresponding EditText, so I don’t have to and didn’t set a default text for EditText (which usually is used as a hint). There is also a button in this activity for submitting this form. I picked some EditTexts as MUST_FILLED ones, so in the button’s custom listener class, I have to check if these MUST_FILLEDs have been filled. follow the intuition I coded as follow:

String s4 = machine_id.getText().toString().trim();
if(s4 == null || s4 == ""){
    Toast.makeText(v.getContext(), 
            "Please Input the machine ID", Toast.LENGTH_SHORT).show();
}

machine_id here is android:id for an EditText. This code ends up with no toast displayed. So I think there is a default text value for EditText even though android:text is not defined manually. Then I wrote a simple project to confirm my thought. Here is the MainActivity.java

public class EditText_testActivity extends Activity implements View.OnClickListener{
/** Called when the activity is first created. */
private String text;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        EditText et = (EditText)findViewById(R.id.et01);
        text = et.getText().toString();

        Button btn = (Button)findViewById(R.id.btn01);
        btn.setOnClickListener(this);
    }

@Override
public void onClick(View v) {
    if(text != null)
        Toast.makeText(v.getContext(), text, Toast.LENGTH_SHORT).show();
    else
        Toast.makeText(v.getContext(), "null", Toast.LENGTH_SHORT).show();

}
}

And main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/et01" />
    <Button 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content"
        android:id="@+id/btn01"
        android:text="TouchMe"/>

</LinearLayout>

It does proved EditText has a default text value, because Toast.makeText(v.getContext(), text, Toast.LENGTH_SHORT).show(); does show a toast. However, it shows something that looks like a blank space but not exactly is.

Finally, I’m wondering what is the default value of android:text in EditText.

Thanks in advance.

Answer 1

I believe the default value is an empty string. It will never be null because if that’s the case, you should already have encountered a NullPointerException at this line:

String s4 = machine_id.getText().toString().trim();

Looking at your code, the reason why the toast did not show up is because you used (s4 == null || s4 == "") as your if condition. == operator is different from .equals().
Try changing your condition to "".equals(s4) instead.