如何使一个机器人微调与初始文本和QUOT;选择一个＆QUOT; [英] How to make an Android Spinner with initial text "Select One"

问题描述

在Android的，我想用一个微调，最初（当用户还没有做出选择还）显示文本选择之一。当用户点击该离心器，将显示的项目列表，并且用户选择的选项之一。当用户做出了选择，选择的项目将显示在微调，而不是选择之一。

In Android, I want to use a Spinner that initially (when the user has not made a selection yet) displays the text "Select One". When the user clicks the spinner, the list of items is displayed and the user selects one of the options. After the user has made a selection, the selected item is displayed in the Spinner instead of "Select One".

我有以下的code创建一个微调：

I have the following code to create a Spinner:

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

通过这个code，最初的项目一显示。我只需要添加一个新的项目选择一个的项目，但随后选择一项也将显示在下拉列表中的第一个项目，这不是我想要的。

With this code, initially the item "One" is displayed. I could just add a new item "Select One" to the items, but then "Select One" would also be displayed in the dropdown list as first item, which is not what I want.

我怎样才能解决这个问题呢？

How can I fix this problem?

推荐答案

下面是一个通用的解决方案，覆盖了微调视图。它将覆盖setAdapter（）来设置初始位置为-1，和代理所提供的SpinnerAdapter显示提示字符串的位置小于0。

Here's a general solution that overrides the Spinner view. It overrides setAdapter() to set the initial position to -1, and proxies the supplied SpinnerAdapter to display the prompt string for position less than 0.

这已经过测试，在Android 1.5至4.2，但买家当心！由于这种解决方案依赖于反射调用私有AdapterView.setNextSelectedPositionInt（）和AdapterView.setSelectedPositionInt（），它不能保证在将来的操作系统更新工作。这很可能是会，但它绝不是保证。

This has been tested on Android 1.5 through 4.2, but buyer beware! Because this solution relies on reflection to call the private AdapterView.setNextSelectedPositionInt() and AdapterView.setSelectedPositionInt(), it's not guaranteed to work in future OS updates. It seems likely that it will, but it is by no means guaranteed.

通常我不会容忍这样的事情，但是这个问题已经被问足够多的次数，这似乎是一个合理的要求不够，我想我会后我的解决方案。

Normally I wouldn't condone something like this, but this question has been asked enough times and it seems like a reasonable enough request that I thought I would post my solution.

/**
 * A modified Spinner that doesn't automatically select the first entry in the list.
 *
 * Shows the prompt if nothing is selected.
 *
 * Limitations: does not display prompt if the entry list is empty.
 */
public class NoDefaultSpinner extends Spinner {

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

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

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

    @Override
    public void setAdapter(SpinnerAdapter orig ) {
        final SpinnerAdapter adapter = newProxy(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);
        }
    }

    protected SpinnerAdapter newProxy(SpinnerAdapter obj) {
        return (SpinnerAdapter) java.lang.reflect.Proxy.newProxyInstance(
                obj.getClass().getClassLoader(),
                new Class[]{SpinnerAdapter.class},
                new SpinnerAdapterProxy(obj));
    }



    /**
     * Intercepts getView() to display the prompt if position < 0
     */
    protected class SpinnerAdapterProxy implements InvocationHandler {

        protected SpinnerAdapter obj;
        protected Method getView;


        protected SpinnerAdapterProxy(SpinnerAdapter obj) {
            this.obj = obj;
            try {
                this.getView = SpinnerAdapter.class.getMethod(
                                 "getView",int.class,View.class,ViewGroup.class);
            } 
            catch( Exception e ) {
                throw new RuntimeException(e);
            }
        }

        public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
            try {
                return m.equals(getView) && 
                       (Integer)(args[0])<0 ? 
                         getView((Integer)args[0],(View)args[1],(ViewGroup)args[2]) : 
                         m.invoke(obj, args);
            } 
            catch (InvocationTargetException e) {
                throw e.getTargetException();
            } 
            catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

        protected View getView(int position, View convertView, ViewGroup parent) 
          throws IllegalAccessException {

            if( position<0 ) {
                final TextView v = 
                  (TextView) ((LayoutInflater)getContext().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE)).inflate(
                      android.R.layout.simple_spinner_item,parent,false);
                v.setText(getPrompt());
                return v;
            }
            return obj.getView(position,convertView,parent);
        }
    }
}

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