Question

I have a custom view that I declare in ‘main’ XML File:

    <com.app.DrawView
    android:id="@+id/my_view"
    android:layout_height="match_parent"
    android:layout_width="match_parent" />

Then in my activity’s onCreate method:

setContentView(R.layout.main);

Which all works fine for displaying the custom view. But what I need to do is pass values to the custom view. So, I tried making an instance of the custom view class:

DrawView drawView = (DrawView) findViewById(R.id.my_view);

Then, in the DrawView class, I created a method:

public void setUserData(boolean data){
      useEraser = data;
}

Now, what my problem is I keep getting a NullPointerExeption when trying to access this method for the DrawView object within my activity, like so:

boolean value = true;
drawView.setUserData(value);

The error points to the “drawView.setUserData(value)” line. What am I doing wrong? I know I must have made a simple mistake but its driving me crazy trying to find it. Any help or suggestions would be great!

EDIT: I accepted an answer which worked correctly, however, I still wanted to know why my original solution did not work. So, I found that, despite the fact that I ordered it correctly in the question, I placed

DrawView drawView = (DrawView)findViewById(R.id.my_view);

before

setContentView(R.layout.main);

I knew it was a simple mistake I was overlooking! Thanks for the answers everyone I appreciate it. And I hope this proves to be useful for anyone faced with a similar problem.

Answer 1

if you want to create new one try this,

put an linearlayout in your xml as a holder

<LinearLayout
        android:id="@+id/ln1"
        android:layout_width="wrap_content"
       android:layout_height="300dp" >

    </LinearLayout>

and in oncreate use below

LinearLayout ln = (LinearLayout)findViewById(R.id.ln1);
         com.example.mixed.DrawView dw2 = new DrawView(getApplicationContext());
         dw2.setUserData(false);
         ln.addView(dw2);

it works there are no problem if you put it in your layout xml.