如何在android中创建一个旋转器？

Question

这是可行的，但是当活动启动时，它会自动提示“One”，因为它是默认选择的。如何使微调框包含实际对话框中不存在的默认值，例如“请选择一个类别”，或者至少不自动选择“一个”。谢谢

final String[] items = new String[] {"One", "Two", "Three"};
        final Spinner catagorySpinner = (Spinner) findViewById(R.id.spinner);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(Expense1.this,
                    android.R.layout.simple_spinner_item, items);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        catagorySpinner.setAdapter(adapter);



        catagorySpinner.setOnItemSelectedListener(new OnItemSelectedListener() {

        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {               
            Toast.makeText(getApplicationContext(), items[position], Toast.LENGTH_SHORT).show();


     }

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

        }});

Answer 1

如果默认情况下未选择任何内容，Android 中的微调器默认显示适配器中的第一个值。不幸的是，没有办法改变它。

在您的情况下，您可以将 Choose a Category 添加到数组中：

final String[] items = new String[] {"Choose a category", "One", "Two", "Three"};

但是在 onItemSelected 中您必须处理这个问题，即：

public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
    if(position != 0)  {
        Toast.makeText(getApplicationContext(), items[position], Toast.LENGTH_SHORT).show();
    }
}

Answer 2

您可以在微调器中手动设置默认选定的项目。

        catagorySpinner.setSelection(2);

Answer 3

这将使数组适配器在单击微调器时发生更改，从而使原来的值消失；在本例中“选择一个类别”

        //final String selected;
        final int a; 
        final int x = 1;
        final ArrayList<String> items = new ArrayList<String>();
        items.add("Select A Category");
        final Spinner catagorySpinner = (Spinner) findViewById(R.id.spinner);
        final ArrayAdapter<String> adapter = new ArrayAdapter<String>(Expense1.this,
                    android.R.layout.simple_spinner_item, items);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        catagorySpinner.setAdapter(adapter);

        final ArrayList<String> itemsTwo = new ArrayList<String>();
        itemsTwo.add("one"); itemsTwo.add("two"); itemsTwo.add("three");

        final ArrayAdapter<String> adapterTwo = new ArrayAdapter<String>(Expense1.this,
                    android.R.layout.simple_spinner_item, itemsTwo);
        adapterTwo.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        /* on spinner click listener (not items inside) */
        catagorySpinner.setOnTouchListener(new OnTouchListener(){
            public boolean onTouch(View v, MotionEvent event) {
                if(event.getAction() == MotionEvent.ACTION_UP){
                    catagorySpinner.setAdapter(adapterTwo);
                            catagorySpinner.setSelection(a);
                    x++;
                }

                return false;
            }
        });

        catagorySpinner.setOnItemSelectedListener(new OnItemSelectedListener() {
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) { 
                // if the spinner has been opened or not 
                 if(x!=1){      
                     a = position;
                    //code to execute if spinner has been clicked and arrayAdapter has been updated
                    //in my case selected = myArray.get(position);

            } else {

                //code to execute if "choose a catagory" is still there
                //in my case selected = "novalue";
            }
        }

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