Question

BUTTON CLICK
1. Modify activity _main.xml to add this Button XML attribute
android:onClick="submit order"
2.replace entire main activity.java file with the file provided in the link to the code
3.run app on device
what happens when you click on the button?

Answer 1

When you click the Button the app will crash at runtime with an IllegalStateException because Android cannot find a method named "submit order(View)" in your Activity.

Why: android:onClick expects a Java method name (no spaces) that exists in the Activity with the signature
public void methodName(View v)
You used the string "submit order" (contains a space), which is not a valid Java identifier and cannot match any declared method, so the framework throws something like:

java.lang.IllegalStateException: Could not find method submit order(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.widget.Button
at android.view.View$DeclaredOnClickListener.resolveMethod(View.java:xxxx)
at android.view.View$DeclaredOnClickListener.onClick(View.java:xxxx)
...

Fixes:
- Change the XML to use a valid method name, e.g. android:onClick="submitOrder"
- Add the matching method in your Activity:
public void submitOrder(View view) {
// handle click
}

If you replace MainActivity.java with the file from the link, make sure that file declares a matching public void method(View) with the same name used in android:onClick.