How to set Spinner default value to null?

问题:

I'm trying to get a Spinner to load up with no selected value. Once the user selects a value it then takes them to another page.

This is proving to be a problem because at present, the page just loads straight away before the user gets a choice to choose.

My spinner class is set up the same way as Google's: http://developer.android.com/resources/tutorials/views/hello-spinner.html

So basically, is it possible have a spinner that loads with nothing selected because at present, it loads the first item in my string array.

回答1:

is it possible have a spinner that loads with nothing selected

Only if there is no data. If you have 1+ items in the SpinnerAdapter, the Spinner will always have a selection.

Spinners are not designed to be command widgets. Users will not expect a selection in a Spinner to start an activity. Please consider using something else, like a ListView or GridView, instead of a Spinner.

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EDIT

BTW, I forgot to mention -- you can always put an extra entry in your adapter that represents "no selection", and make it the initial selected item in the Spinner.

回答2:

Alternatively, you could override your spinner adapter, and provide an empty view for position 0 in your getView method, and a view with 0dp height in the getDropDownView method.

This way, you have an initial text such as "Select an Option..." that shows up when the spinner is first loaded, but it is not an option for the user to choose (technically it is, but because the height is 0, they can't see it).

回答3:

This is a complete implementation of Paul Bourdeaux's idea, namely returning a special initial view (or an empty view) in getView() for position 0.

It works for me and is relatively straightforward. You might consider this approach especially if you already have a custom adapter for your Spinner. (In my case, I was using custom adapter in order to easily customise the layout of the items, each item having a couple of TextViews.)

The adapter would be something along these lines:

public class MySpinnerAdapter extends ArrayAdapter {      public MySpinnerAdapter(Context context, List items) {         super(context, R.layout.my_spinner_row, items);     }      @Override     public View getDropDownView(int position, View convertView, @NonNull ViewGroup parent) {         if (position == 0) {             return initialSelection(true);         }         return getCustomView(position, convertView, parent);     }      @NonNull     @Override     public View getView(int position, View convertView, @NonNull ViewGroup parent) {         if (position == 0) {             return initialSelection(false);         }         return getCustomView(position, convertView, parent);     }       @Override     public int getCount() {         return super.getCount() + 1; // Adjust for initial selection item     }      private View initialSelection(boolean dropdown) {         // Just an example using a simple TextView. Create whatever default view          // to suit your needs, inflating a separate layout if it's cleaner.         TextView view = new TextView(getContext());         view.setText(R.string.select_one);         int spacing = getContext().getResources().getDimensionPixelSize(R.dimen.spacing_smaller);         view.setPadding(0, spacing, 0, spacing);          if (dropdown) { // Hidden when the dropdown is opened             view.setHeight(0);         }          return view;     }      private View getCustomView(int position, View convertView, ViewGroup parent) {         // Distinguish "real" spinner items (that can be reused) from initial selection item         View row = convertView != null && !(convertView instanceof TextView)          ? convertView :         LayoutInflater.from(getContext()).inflate(R.layout.my_spinner_row, parent, false);          position = position - 1; // Adjust for initial selection item         MyModel item = getItem(position);          // ... Resolve views & populate with data ...          return row;     }  } 

That's it. Note that if you use a OnItemSelectedListener with your Spinner, in onItemSelected() you'd also have to adjust position to take the default item into account, for example:

if (position == 0) {     return; } else {     position = position - 1; } MyModel selected = items.get(position); 

回答4:

In my case, although size '2' is displayed in the spinner, nothing happens till some selection is done!

I have an xml file (data_sizes.xml) which lists all the spinner values.

2481632

In main.xml file: Spinner element

Then in my java code, I added:

In my activity: Declaration

Spinner spinnerSize; ArrayAdapter adapter; 

In a public void function - initControls(): Definition

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()); 

My spinner listener:

/* Spinner Listener */

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     } } 

回答5:

Using a custom spinner layout like this:

In the activity:

    // populate the list     ArrayList dataList = new ArrayList();     for (int i = 0; i  dataAdapter = new ArrayAdapter(this, R.drawable.spinner_layout, dataList);     dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);     spinnerObject.setAdapter(dataAdapter);     spinnerObject.setOnTouchListener(new View.OnTouchListener() {           public boolean onTouch(View v, MotionEvent event) {             // to set value of first selection, because setOnItemSelectedListener will not dispatch if the user selects first element             TextView spinnerTarget = (TextView)v.findViewById(R.id.spinnerTarget);             spinnerTarget.setText(spinnerObject.getSelectedItem().toString());              return false;         }      });     spinnerObject.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {                 private boolean selectionControl = true;                  public void onItemSelected(AdapterView> parent, View view, int pos, long id) {                     // just the first time                     if(selectionControl){                          // find TextView in layout                          TextView spinnerTarget = (TextView)parent.findViewById(R.id.spinnerTarget);                         // set spinner text empty                         spinnerTarget.setText("");                         selectionControl = false;                     }                     else{                         // select object                     }                 }                  public void onNothingSelected(AdapterView> parent) {                  }             }); 

回答6:

you can put the first cell in your array to be empty({"","some","some",...}) and do nothing if the position is 0;

public void onItemSelected(AdapterView> parent, View view, int position, long id) {     if(position>0) {         label.setText(MainActivity.questions[position - 1]);     } } 

• if you fill the array by xml file you can let the first item empty

回答7:

My solution, in case you have a TextView as each row of the spinner:

    // TODO: add a fake item as the last one of "items"     final ArrayAdapter adapter=new ArrayAdapter(..,..,items)        {       @Override       public View getDropDownView(final int position,final View convertView,final ViewGroup parent)         {         final View dropDownView=super.getDropDownView(position,convertView,parent);         ((TextView)dropDownView.findViewById(android.R.id.text1)).setHeight(position==getCount()-1?0:getDimensionFromAttribute(..,R.attr.dropdownListPreferredItemHeight));         dropDownView.getLayoutParams().height=position==getCount()-1?0:LayoutParams.MATCH_PARENT;         return dropDownView;         }       }      ...     spinner.setAdapter(adapter);     _actionModeSpinnerView.setSelection(dataAdapter.getCount()-1,false);      public static int getDimensionFromAttribute(final Context context,final int attr)     {     final TypedValue typedValue=new TypedValue();     if(context.getTheme().resolveAttribute(attr,typedValue,true))       return TypedValue.complexToDimensionPixelSize(typedValue.data,context.getResources().getDisplayMetrics());     return 0;     } 

回答8:

Merge this:

private long previousItemId = 0;  @Override public long getItemId(int position) {     long nextItemId = random.nextInt(Integer.MAX_VALUE);     while(previousItemId == nextItemId) {         nextItemId = random.nextInt(Integer.MAX_VALUE);     }     previousItemId = nextItemId;     return nextItemId; } 

With this answer:

public class SpinnerInteractionListener         implements AdapterView.OnItemSelectedListener, View.OnTouchListener {      private AdapterView.OnItemSelectedListener onItemSelectedListener;      public SpinnerInteractionListener(AdapterView.OnItemSelectedListener selectedListener) {         this.onItemSelectedListener = selectedListener;     }      boolean userSelect = false;      @Override     public boolean onTouch(View v, MotionEvent event) {         userSelect = true;         return false;     }      @Override     public void onItemSelected(AdapterView> parent, View view, int pos, long id) {         if(userSelect) {             onItemSelectedListener.onItemSelected(parent, view, pos, id);             userSelect = false;         }     }      @Override     public void onNothingSelected(AdapterView> parent) {         if(userSelect) {             onItemSelectedListener.onNothingSelected(parent);             userSelect = false;         }     } } 

文章来源: How to set Spinner default value to null?