Add button to a layout programmatically

Question

I m having trouble adding a button to a layout that I ve created in XML  Here s what I want to achieve     some class else           startActivity new Intent StatisticsScreen this  ScreenTemperature class              ScreenTemperatureClass  Override public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState          this is where I call another class that       displays a nice graph     setContentView new GraphTemperature getApplicationContext           I want to add a Button to this new screen so that it ll appear below the graph  I ve tried creating a LinearLayout view  then create a Button and add it to this view but I just get NullPointerExceptions    Any help would be appreciated  Thanks  EDIT 1  Here s what I ve tried using that created a NullPointerException and  force close    Button buybutton  LinearLayout layout    Override public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState        setContentView new GraphTemperature getApplicationContext           layout    LinearLayout  findViewById R id statsviewlayout       Button buyButton   new Button this       buyButton setText R string button back       buyButton setLayoutParams new LayoutParams          ViewGroup LayoutParams WRAP CONTENT              ViewGroup LayoutParams WRAP CONTENT        layout addView buyButton        And here s the logcat error   ERROR AndroidRuntime 293   java lang RuntimeException  Unable to start activity ComponentInfo com weatherapp com weatherapp ScreenTemperature   java lang NullPointerException ERROR AndroidRuntime 293       at android app ActivityThread performLaunchActivity ActivityThread java 2663  ERROR AndroidRuntime 293       at android app ActivityThread handleLaunchActivity ActivityThread java 2679  ERROR AndroidRuntime 293       at android app ActivityThread access 2300 ActivityThread java 125  ERROR AndroidRuntime 293       at android app ActivityThread H handleMessage ActivityThread java 2033    theres abviously more lines to do with this error in logcat  not sure if you want it   EDIT 2  So i tried bhups method    Override public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       GraphTemperature GT   new GraphTemperature getApplicationContext                      layout    LinearLayout  findViewById R id statsviewlayout       Button buyButton   new Button this       buyButton setText R string button back       buyButton setLayoutParams new LayoutParams          ViewGroup LayoutParams WRAP CONTENT              ViewGroup LayoutParams WRAP CONTENT        layout addView GT      line 27     layout addView buyButton              setContentView layout                  This method produced the same logcat error as above  NullPointerException  indicating it was something to do with line no  27 which is the layout addView line of code  Any ideas  Thanks again

User · Accepted Answer

This line   layout    LinearLayout  findViewById R id statsviewlayout     Looks for the  statsviewlayout  id in your current  contentview   Now you ve set that here   setContentView new GraphTemperature getApplicationContext        And i m guessing that new  graphTemperature  does not set anything with that id   It s a common mistake to think you can just find any view with findViewById  You can only find a view that is in the XML  or appointed by code and given an id    The nullpointer will be thrown because the layout you re looking for isn t found  so  layout addView buyButton     Throws that exception   addition  Now if you want to get that view from an XML  you should use an inflater   layout    LinearLayout  View inflate this  R layout yourXMLYouWantToLoad  null     assuming that you have your linearlayout in a file called  yourXMLYouWantToLoad xml

User · Answer

If you just have included a layout file at the beginning of onCreate   inside setContentView and want to get this layout to add new elements programmatically try this   ViewGroup linearLayout    ViewGroup  findViewById R id linearLayoutID     then you can create a new Button for example and just add it   Button bt   new Button this   bt setText  A Button    bt setLayoutParams new LayoutParams LayoutParams FILL PARENT                                       LayoutParams WRAP CONTENT    linerLayout addView bt

[android] Add button to a layout programmatically

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