Android Multiple Spinner更新

Question

Okay, so I'm working on an android app. In one of my app's activities (called convert), there are already 3 blank spinners (We'll ignore the third one for now). One main spinner lets the user decide on a topic such as temperature, pressure, or volume.

public class Convert extends Activity{
    String category = MySingleton.getInstance().getCategory();
    protected DataStorage appState;
    public void onCreate(Bundle icicle){
        super.onCreate(icicle);
        setContentView(R.layout.convert);

        appState = (DataStorage)getApplication();

        // Category Info
        Spinner convertTopic = (Spinner) findViewById(R.id.convertTopic);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.convertTopic_array, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        convertTopic.setAdapter(adapter);

        category = MySingleton.getInstance().getCategory();
        // Subcategory Info
        Spinner inputUnit = (Spinner) findViewById(R.id.inputUnit);
        ArrayAdapter<CharSequence> adapter2;
        adapter2 = ArrayAdapter.createFromResource(this, R.array.blank_array, android.R.layout.simple_spinner_item);
        if(category.equals("Temperature"))
            adapter2 = ArrayAdapter.createFromResource(this, R.array.convertUnitTemperature_array, android.R.layout.simple_spinner_item);
        else if(category.equals("Pressure"))
            adapter2 = ArrayAdapter.createFromResource(this, R.array.convertUnitPressure_array, android.R.layout.simple_spinner_item);
        else if(category.equals("Volume"))
            adapter2 = ArrayAdapter.createFromResource(this, R.array.convertUnitVolume_array, android.R.layout.simple_spinner_item);

        adapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        inputUnit.setAdapter(adapter2);

        convertTopic.setOnItemSelectedListener(new OnTopicSelectedListener());
    }
}

I also have a separate class that handles my first spinner selection.

public class OnTopicSelectedListener implements OnItemSelectedListener{
    String category = MySingleton.getInstance().getCategory();
    protected DataStorage appState;

    public void onItemSelected(AdapterView<?> parent, View view, int pos, long id){
        if(parent.getItemAtPosition(pos).toString().length() != 0){
            Toast.makeText(parent.getContext(), "Working with " +
                parent.getItemAtPosition(pos).toString(), Toast.LENGTH_LONG).show();
        }
       category = parent.getItemAtPosition(pos).toString();
       MySingleton.getInstance().setCategory(category);
    }

    @SuppressWarnings("rawtypes")
    public void onNothingSelected(AdapterView parent){
        // Do nothing.
    }
}

My issue is rather simple but I haven't found a solution to it. Whenever that activity starts, everything is blank as expected. However, whenever someone selects an option from the main spinner convertTopic , the second spinner won't update.

The only way I can get the second spinner to update is to return to the previous activity and go back to the Convert activity. The main spinner will appear blank again but the second spinner is updated.

I want to make it so the second spinner updates the selection as soon as the user selects something from the main spinner. Is there any method I could use do this? Are there any loops involved?

I apologize if my question isn't clear. This is my first time asking a question on this website.

Answer 1

Instead of making the OnItemSelectedListener a separate class, make it an inner class of Convert . Then make your spinner variables members of Convert instead of just local variables within onCreate . Now your inner class will have direct access to the second spinner thus allowing you to manipulate it from within the onItemSelected method.

For a non-android explanation of inner class you can refer to the Java Tutorials here .