Adding a button in linear layout crashes

Question

I really do not understand why this simple code crashes in this line layout.addView(button);

super.onCreate(savedInstanceState);
    layout = (LinearLayout)findViewById(R.id.linearLayout);
    LinearLayout.LayoutParams p = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT);

    Button button = new Button(this);
    button.setHeight(100);
    button.setWidth(100);
    button.setText("HELLO");
    button.setLayoutParams(p);
    layout.addView(button);

activity_main.xml

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/linearLayout">
</LinearLayout>

EDIT: edited code still crushes. But now crushes in setContentView.

super.onCreate(savedInstanceState);

    layout = (LinearLayout)findViewById(R.id.linearLayout);
    setContentView(layout); 
    LayoutParams p = new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT);

    int i,j;
    Button button = new Button(this);
    button.setHeight(100);
    button.setWidth(100);
    button.setText("HELLO");
    layout.addView(button,p);

Logcat report enter image description here

you have to call setContentView BEFORE findViewById not AFTER — Blackbelt
– Blackbelt, Commented Apr 8, 2013 at 15:04
Then how am I gonna give the layout as argument in setContentView? I have to get it from the xml first right by doing findViewById? — Tahlil
– Tahlil, Commented Apr 8, 2013 at 15:06
can't you simply do setContentView(R.layout.activity_main) ? — Blackbelt
– Blackbelt, Commented Apr 8, 2013 at 15:07
Thanks blackbelt it works :) But suppose activity_main.xml had two or three layouts. And I wanted to get only one of them as my layout for the activity. how can I do that? — Tahlil
– Tahlil, Commented Apr 8, 2013 at 15:12
I am glad it works. your question does not make sense to me. — Blackbelt
– Blackbelt, Commented Apr 8, 2013 at 15:16

Egor · Accepted Answer · 2013-04-08 14:56:07Z

5

Simply because you haven't called setContentView(). The root View of your Activity is null, so is layout.

answered Apr 8, 2013 at 14:56

Egor

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4 Comments

Egor Over a year ago

@kalkin, You need to call setContentView() before doing any findViewById() calls.

mihail Over a year ago

usually the call looks like setContentView(R.layout.yourLayout), the value of the layout variable is probably not a valid layout id

Tahlil Over a year ago

but I added that id in the activity_main.xml. And if I do setContentView(R.layout.yourLayout) then after that how am I gonna access yourlayout from java code so that later I can add buttons and stuff in it?

mihail Over a year ago

This is just example code. You better read some basics on how android works - maybe here: developer.android.com/training/basics/firstapp/index.html

Graeme · Accepted Answer · 2013-04-08 15:07:49Z

0

You're specifying the Views width height here:

button.setHeight(100);
button.setWidth(100);

then immediately overwriting it:

button.setLayoutParams(p);

try this, remove the setWidth and setLayoutParams and remove p:

  layout.addView(button, new LayoutParams(100,100));

edited Apr 8, 2013 at 15:07

answered Apr 8, 2013 at 14:56

Graeme

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3 Comments

Tahlil Over a year ago

Hi I edited as you mentioned. But it crushes in the setContentView. thanks.

Graeme Over a year ago

Edited my answer, sorry, missed one of your lines in the question

Graeme Over a year ago

... Ah.. "Crushes" - you mean "Crashes" I thought the button was being crushed. :)

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