When are closing tags required with Android view m

问题:

For some Android XML attributes, you don't conclude the opening tag with a '>' until after you've inserted your formatting components. For example:

<EditText 
  android:id="@+id/etEmails"> 
</EditText>

Why is there no definition for the EditText component within the opening and closing tags? Also, I noticed that some don't even require closing tags and are just in themselves XML statements. For example:

<Button
  android:text="Subtract 1"
  android:id="@+id/buttSub"
  />

Why does this XML statement not require a closing statement when it practically provides the same components as the EditText field?

• Is there a failsafe way of knowing which ones require opening and closing statements for proper syntax?

• Is there a list/reference for which ones do and don't?

• What's the difference between these different components?

回答1:

The <Button /> is a so called short tag. This is safe.

If a tag has no body you can obmit the closing tag and add a slash at the end of the tag which means here this tag has no children.

This notation is very common in xhtml for <br /> and <img src="" alt="" /> tags.

The benifit is that you don't need to write the closing tag which makes it simpler to read and if you have a huge xml file there are less data to transport. (This does not count for Android is this case, because the android SDK procudes internally a binary file.)

回答2:

If no other element like this for example <something></something> is inside another element then the end tag /> can be used. So in your example the EditText can end also with the /> tag.

When you want to add another element to your EditText then you need to close the XML of EditText with .

回答3:

for '>' write in XML

please write as mention below

android:text="Subtract > 1"