删除空arraylist中的元素会使我的应用程序崩溃

Question

I have an arraylist for my spinner, 1 add button to add element into the list and 1 delete button to delete the element inside the list. The elements that I added into the list will show in the spinner. Initially the arraylist is empty with nothing inside. When it is empty and I press the delete button, means that I am trying to delete elements in a arraylist with no element inside and this makes my app crashes.

So, I wanted to add a toast to replace the delete function when the list is empty. When the list is not empty, then the delete function will come back.

Any solution for this?

    spinner = (Spinner) findViewById(R.id.spinner1);
    adp = new ArrayAdapter<String>(CarSelection.this,android.R.layout.simple_spinner_item, list);
    adp.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(adp);
    spinner.setOnItemSelectedListener(
                new OnItemSelectedListener() {
                    public void onItemSelected(
                        AdapterView<?> parent, View view, final int position, long id) {
                            Button delete = (Button) findViewById(R.id.delete);

                            View.OnClickListener del = new View.OnClickListener() {

                                @Override
                                public void onClick(View view) {
                                    list.remove(position);
                                }

Answer 1

Lets say, your ArrayList is called mList , your delete function should look something like -

public void deleteElement(int pos) {

    if(mList.isEmpty()) {
        //Toast
        Toast.makeText(yourContext, "Ooi, list is empty", Toast.LENGTH_SHORT).show();
    } else {
        mList.remove(pos);
    }
}

UPDATE

@Override                                
public void onClick(View view) {

    if(list.isEmpty()) {
        //Your Toast
        Toast.makeText(yourContext, "Ooi, list is empty", Toast.LENGTH_SHORT).show();
    } else {
        list.remove(position);
    }
}

Answer 2

Firstly,IMHO for better UX, you should not display the spinner if the list is empty .You can show toast message to the user saying that you cant perform this operation.

Anyways here is the code snippet you can use to do the check.You can put this check in whichever place you want

 if(!list.isEmpty())
      //list is empty
    else
     list is not empty

Answer 3

You should test for the "empty" case. Supposing an array named "elements":

if elements.isEmpty() {
  deleteButton.disable();
}

The best is to disable the delete button when there is no elements in the array.