如何将整数传递给类的实例并使用它来调用另一个类的方法？

Question

here's activity 1 which is a listview. when the user clicks on an item, I want the item clicked to launch an instance of a class and pass an int value to it, which will later be used in a switch.

       @Override
    public void onItemClick(AdapterView<?> adapter, View view,
                int position, long id) {


    switch(position){

   case 0:


       Intent g = new Intent(books.this, SpecificBook.class);
       Bundle b = new Bundle();
       b.putInt("dt", 0);
       g.putExtras(b);
       books.this.startActivity(g);
       break;

    case 1: 
        Intent ex = new Intent(books.this, SpecificBook.class);
       Bundle b1 = new Bundle();
       b1.putInt("dt", 1);
       ex.putExtras(b1);
       books.this.startActivity(ex);
      break;

      //etc.

here's activity 2, which is supposed to retrieve the int value and call the appropriate method from the database helper class.

      public class SpecificBook extends Activity {

       private DatabaseHelper Adapter;

Intent myLocalIntent = getIntent();
 Bundle myBundle = myLocalIntent.getExtras();
  int dt = myBundle.getInt("dt");

 @SuppressWarnings("deprecation")
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
  setContentView(R.layout.listy);


ListView lv = (ListView)findViewById(R.id.listview);     
 Adapter = new DatabaseHelper(this);
 Adapter.open();    
 Cursor cursor = null;


switch(dt){
 case 0:cursor = DatabaseHelper.getbook1Data(); break;
 case 1:cursor = DatabaseHelper.getbook2Data(); break;
  //etc.
}

startManagingCursor(cursor);

etc.

The database methods are queries. Basically, I want each item in the book class listview to run it's own query based on the item selected and display the results. I get a "source not found" and runtimeexception error. where am i going wrong? is there a better way to go about this?

I have already tried the "getter and setter" way to no avail. I've also tried the "putextra" method on the instance of the intent but that didn't work.

Answer 1

The earliest you can access an Intent is in onCreate() :

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.listy);

    Intent myLocalIntent = getIntent();
    Bundle myBundle = myLocalIntent.getExtras();
    int dt = myBundle.getInt("dt");

---

You should check if the Intent or Bundle is null and if you only want the one item from your Intent you can use:

Intent myLocalIntent = getIntent();
if(myLocalIntent != null) {
    int dt = myLocalIntent.getIntExtra("dt", -1); // -1 is an arbitrary default value
}

Lastly, you don't need to create a new Bundle to pass values in an Intent and it looks like you simply want to pass the position ... So you can drastically shorten your onItemClick() method:

@Override
public void onItemClick(AdapterView<?> adapter, View view, int position, long id) {
    Intent g = new Intent(books.this, SpecificBook.class);
    g.putInt("dt", position);
    books.this.startActivity(g);
}