在LinearLayout中动态创建多个TextView

Question

I want to create multiple TextView s inside a LinearLayout .The following code builds successfully but gives a NullPointerException at the line root.addView(t[i]);

public class MainActivity extends ActionBarActivity {
    TextView t[];
    LinearLayout root;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        root=(LinearLayout)findViewById(R.id.master);
        t=new TextView[10];
       LinearLayout.LayoutParams dim=new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
        for(int i=0;i<10;i++)
        {
            t[i]=new TextView(this);
            t[i].setLayoutParams(dim);
            t[i].setText("YOHOHO: "+i);
            root.addView(t[i]);
        }
        setContentView(root);
    }

This really has no aim Iam just trying to learn things!

Answer 1

It's giving NPE because you are not setting your activity layout properly.

Do this

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.whereLinearLayoutMasterIs); // Add your layout here
    root=(LinearLayout)findViewById(R.id.master);
    t=new TextView[10];
   LinearLayout.LayoutParams dim=new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
    for(int i=0;i<10;i++)
    {
        t[i]=new TextView(this);
        t[i].setLayoutParams(dim);
        t[i].setText("YOHOHO: "+i);
        root.addView(t[i]);
    }
}

NOTE R.layout.whereLinearLayoutMasterIs is indicative, use your layout in which R.id.master is

Answer 2

The problem is that root is null - this is because you've not yet set your Activity's content view via setContentView . You need to do something like this:

super.onCreate(...); setContentView(R.layout.yourLayoutName); root=(LinearLayout)findViewById(R.id.master);