I'm Trying do change an layout if the user press a button but on the method setOnClickListener raises an exception "java.lang.nullPointer exeception
meu codigo abaixo

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public class ChangeLayout extends Activity{
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);
       
        btnNovo = (Button)findViewById(R.id.btnNovo);

        btnNovo.setOnClickListener( new Button.OnClickListener(){

         @Override
         public void onClick(View arg0) {
            
            setContentView(R.layout.start);
                       }
         }
}

}


what is wrong?

thanks for you attention

Hi,

I use the following for OnClickListeners on my buttons



Notice that I use the View.OnClickListener

Hello felix,

an essential information is where/when the error occurs.

I never tried it myself, but I found two hints in the sdk, that it maybe is only possible within onCreate():

When Android compiles your application, it compiles each file into an android.view.View resource that you can load in code by calling setContentView(R.layout.layout_file_name) in your Activity.onCreate() implementation.

onCreate(Bundle) is where you initialize your activity. Most importantly, here you will usually call setContentView(int) with a layout resource defining your UI, and using findViewById(int) to retrieve the widgets in that UI that you need to interact with programmatically.

BUT there at least exists a function that indicates that is maybe posbbile:

onContentChanged()
This hook is called whenever the content view of the screen changes (due to a call to setContentView().)

So let us know on which line the exception is thrown (directly when you start your app or just when clicking the button).

Regards,
plusminus

oh shit, i'm not using the tag "andoid:id" and my button is set with null, changing this atributte on the button it's work



thanks for your help

felix wrote:oh shit, i'm not using the tag "andoid:id" and my button is set with null, changing this atributte on the button it's work



thanks for your help

yeah thats a pain with the new m5 SDK, after you change it once i'm sure you will remember.

res wrote:

felix wrote:oh shit, i'm not using the tag "andoid:id" and my button is set with null, changing this atributte on the button it's work



thanks for your help

yeah thats a pain with the new m5 SDK, after you change it once i'm sure you will remember.

But I think it was a simplification. Definitely in AndroidManifest. Almost all tags are now "android:name", thats easier to learn.

Regards,
plusminus