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 `NullPointerException`s.. 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(getApplication…

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"

Add button to a layout programmatically

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