无法在我的项目中解决运行时异常

Question

我正在开发一个小项目，我得到一个错误，无法解决显示强制关闭应用程序。任何人都可以帮助我

这是我的screen3代码

public class screen3 extends ListActivity {
    /** Called when the activity is first created. */
    String[] names = new String[] { "India", "Malaysia"};
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.screen3);
        // Create an array of Strings, that will be put to our ListActivity

        // Use your own layout and point the adapter to the UI elements which
        // contains the label
        this.setListAdapter(new ArrayAdapter<String>(this, R.layout.screen3,
                R.id.label, names));
        Button b4=(Button)findViewById(R.id.click);
        b4.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent i2 =new Intent(screen3.this,screen4.class);
                startActivity(i2);
            }
        });
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);
        // Get the item that was clicked
        Object o = this.getListAdapter().getItem(position);
        String keyword = o.toString();
        if(keyword.equals("India"))
        {
            Intent i=new Intent(screen3.this,new21.class);
            startActivity(i);

        }
        Toast.makeText(this, "You selected: " + keyword, Toast.LENGTH_LONG)
                .show();

    }

}

和 26行代码是

public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent i2 =new Intent(screen3.this,screen4.class);
                startActivity(i2);

我检查过它很好

Answer 1

在Screen3 onCreate方法中，第26行有一个空指针异常...