Android Spinner - How to default list selection to

问题:

This question already has an answer here:

• How to make an Android Spinner with initial text “Select One”? 36 answers

I have an Android form that needs to update itself based on certain selections. The form is currently made up of 2 Spinners (A and B). Spinner B not created until Spinner A's selection is made. After the selection is made B will be displayed to the view and it's contents dynamically filled based on A's selection. Here is my code:

public class MyForm extends Activity 
{   
    private final int SEL_ACTIVATE = 0;
    private final int SEL_DEACTIVATE = 1;

    private static final String[] actionList = {"Activate", "Deactivate" };

    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        table = (TableLayout) findViewById(R.id.table);

        showListA(table);
    }

    public void showListA(View v)
    {        
        rowAction = new TableRow(this);

        Spinner spinner = new Spinner(this);
        spinner.setPrompt("Select...");
        spinner.setOnItemSelectedListener(
            new OnItemSelectedListener() 
            {
                public void onItemSelected(AdapterView<?> parent, View v, int position, long id) 
                {
                    switch (position)
                    {
                    case SEL_ACTIVATE:
                    case SEL_DEACTIVATE:
                        showListB(v);
                        break;
                    }
                }

                public void onNothingSelected(AdapterView<?> arg0) 
                {
                    // TODO Auto-generated method stub
                }
        });

        ArrayAdapter<String> adapter = new ArrayAdapter<String> (this, android.R.layout.simple_spinner_item, actionList);
        adapter.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
        spinner.setAdapter(adapter);

        rowAction.addView(tvAction);
        rowAction.addView(spinner);

        table.addView(rowAction, new TableLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
    }

    ...
}

This code works correctly. When either "Activate" or "Deactivate" are selected from the list, showListB() executes which is very similar to showListA() in how it creates a new row which contains Label and Spinner.

The problem is that, by default, "Activate" is shown in the Spinner which executes showListB() and right off the bat, the second part of the form is created based on the "Activate" option. The only workaround that I can come up with is to add a third field to the Spinner like so:

private static final String[] actionList = {"None", "Activate", "Deactivate" };

...

switch (position)
{
case SEL_NONE:
    break;
case SEL_ACTIVATE:
case SEL_DEACTIVATE:
    showListB(v);
    break;
}

This works... but I don't want a third option in the list. I just want it to, by default, be blank or show some sort of 'prompt' text that is not an option in the list once it is pressed. Is this possible?

Thanks

EDIT:

xml content:

<Spinner
    android:id="@+id/spinnerAction"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>  

回答1:

My data-sizes.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="chunks">
        <item>2</item>
        <item>4</item>
        <item>8</item>
        <item>16</item>
        <item>32</item>
    </string-array>
</resources>

In main.xml:

<Spinner android:id="@+id/spinnerSize"  
android:layout_marginLeft="50px"
android:layout_width="fill_parent"                  
android:drawSelectorOnTop="true"
android:layout_marginTop="5dip"
android:prompt="@string/SelectSize"
android:layout_marginRight="30px"
android:layout_height="35px" /> 

In Java Code:

Spinner spinnerSize;
ArrayAdapter adapter;

...

spinnerSize = (Spinner)findViewById(R.id.spinnerSize);
adapter = ArrayAdapter.createFromResource(this, R.array.chunks, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinnerSize.setAdapter(adapter);
spinnerSize.setOnItemSelectedListener(new MyOnItemSelectedListener());

...

class MyOnItemSelectedListener implements OnItemSelectedListener {

    public void onItemSelected(AdapterView<?> parent,
        View view, int pos, long id) {
        chunkSize = new Integer(parent.getItemAtPosition(pos).toString()).intValue();
    }
    public void onNothingSelected(AdapterView<?> parent) {
      // Dummy
    }
}

So, although I can see 2 as my first default item, nothing happens unless user actually selects it.

Hope this helps!

回答2:

If you want, there is a decorater spinnerAdapter witch add automatically a default value :

    protected class SpinnerAdapterWithNoValue implements SpinnerAdapter {

        private SpinnerAdapter _current;
        private final static String defaultValue = "Choisir";

        public SpinnerAdapterWithNoValue(SpinnerAdapter base) {
            _current = base;
        }

        @Override
        public int getCount() {
            return _current.getCount() + 1;
        }

        @Override
        public Object getItem(int position) {
            if (position == 0 || position == -1) {
                return null;
            }
            return _current.getItem(position - 1);
        }

        @Override
        public long getItemId(int position) {
            if (position == 0 || position == -1) {
                return -1;
            }
            return _current.getItemId(position - 1);
        }

        @Override
        public int getItemViewType(int position) {
            if (position == 0 || position == -1) {
                return -1;
            }
            return _current.getItemViewType(position - 1);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (position == 0 || position == -1) {
                final TextView v = (TextView) ((LayoutInflater) getContext().getSystemService(
                        Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.spinner_text, parent, false);
                v.setText(defaultValue);
                return v;
            }
            return _current.getView(position - 1, convertView, parent);
        }

        @Override
        public int getViewTypeCount() {
            return _current.getViewTypeCount();
        }

        @Override
        public boolean hasStableIds() {
            return _current.hasStableIds();
        }

        @Override
        public boolean isEmpty() {
            return _current.isEmpty();
        }

        @Override
        public void registerDataSetObserver(DataSetObserver observer) {
            _current.registerDataSetObserver(observer);
        }

        @Override
        public void unregisterDataSetObserver(DataSetObserver observer) {
            // TODO Auto-generated method stub
            _current.unregisterDataSetObserver(observer);
        }

        @Override
        public View getDropDownView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            if (position == 0 || position == -1) {
                CheckedTextView v = (CheckedTextView) ((LayoutInflater) getContext().getSystemService(
                        Context.LAYOUT_INFLATER_SERVICE)).inflate(android.R.layout.simple_spinner_dropdown_item, parent,
                        false);
                v.setText(defaultValue);
                return v;
            }
            return _current.getDropDownView(position - 1, convertView, parent);
        }
    }

Then you can create your own spinner using this decorater :

    public class SpinnerWithNoValue extends Spinner {

        public SpinnerWithNoValue(Context context) {
            super(context);
        }

        public SpinnerWithNoValue(Context context, AttributeSet attrs) {
            super(context, attrs);
        }

        public SpinnerWithNoValue(Context context, AttributeSet attrs, int defStyle) {
            super(context, attrs, defStyle);
        }

        @Override
        public void setAdapter(SpinnerAdapter orig) {
            final SpinnerAdapter adapter = new SpinnerAdapterWithNoValue(orig);
            super.setAdapter(adapter);

            try {
                final Method m = AdapterView.class.getDeclaredMethod("setNextSelectedPositionInt", int.class);
                m.setAccessible(true);
                m.invoke(this, -1);

                final Method n = AdapterView.class.getDeclaredMethod("setSelectedPositionInt", int.class);
                n.setAccessible(true);
                n.invoke(this, -1);

            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

        /*
         * getSelectedItem renvoi null si la valeur par defaut est séléctionnée
         * 
         * @see android.widget.AdapterView#getSelectedItem()
         */
        @Override
        public Object getSelectedItem() {
            return super.getSelectedItem();
        }
    }

You just have to change the spinner declaration in your xml layout :

com.myproject.SpinnerWithNoValue

If you want, you can change the code to set the default text in the tag of your spinner.

回答3:

The Spinner will always have a selection. What you can do is make the Spinner display something like "Select"or "Select a option"...

To do this you can make your list options to be

actionList = {"Select", "Desactivate" }

and

public void onItemSelected(AdapterView<?> arg0, View arg1, int position, long id) {               
        actionList[0] = "Activate";
        ...
 }

or you can do something more complicated like overrides the Spinner View or put a button instead with nothing on it and when it's clicked you create your spinner.

回答4:

Try setting this in xml with the prompt attribute:

android:prompt="@string/prompt"

This will also fill in the top of the spinner dialog.

I overlooked this in the documentation. The prompt can not be directly applied. The prompt attribute has to be referenced from another source. Try referencing a string value.

Documentation from Android:

android:prompt

Since: API Level
 The prompt to display when the spinner's dialog is shown.
 Must be a reference to another resource, in the form "@[+][package:]type:name" or to a       theme attribute in the form "?[package:][type:]name".
This corresponds to the global attribute resource symbol prompt.

回答5:

I'm just a begginner at android app development, and was facing a similar problem; was able to sort it out using a simple solution- this worked for me, hope it does for you also:

public class AdmissionActivity extends Activity implements OnItemSelectedListener{

int i;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    i=0;
            .........

           }

........ .....

public void onItemSelected(AdapterView<?> parent, View view, 
        int pos, long id){

    if(i!=0){
        //do wat you want;
    }
    else i=1;
            }
            //initially the activity will be loaded and nothing  will happen (since
              // i=0); and then appropriate action will be taken since i would hav been

// changed to sumtng else