Android Spinner – 如何将列表选择默认为无

参见英文答案 > How to make an Android Spinner with initial text “Select One”35个
我有一个Android表单需要根据某些选择更新自己.该表格目前由2个Spinners(A和B)组成.在完成Spinner A的选择之前,不会创建微调器B.选择完成后,B将显示在视图中,并根据A的选择动态填充内容.这是我的代码：

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));
    }

    ...
}

此代码正常工作.当从列表中选择“激活”或“取消激活”时,showListB()执行与showListA()非常相似的创建包含Label和Spinner的新行.

问题是,默认情况下,Spinner中会显示“Activate”,执行showListB()并直接执行,表单的第二部分是基于“Activate”选项创建的.我能想到的唯一解决方法是向Spinner添加第三个字段,如下所示：

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

...

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

这有效……但我不希望列表中有第三个选项.我只是希望它默认为空白或显示某种“提示”文本,一旦按下它就不是列表中的选项.这可能吗？

谢谢

编辑：

xml内容：

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

<?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>

<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" />

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
    }
}