我想使用一个微调器,最初(当用户还没有做出选择时)显示文本“Select One”。当用户单击微调器时,将显示项目列表,用户可以选择其中一个选项。用户做出选择后,所选项目将显示在微调器中,而不是“Select One”。
我有以下代码来创建一个旋转器:
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);
使用这段代码,最初会显示项目“One”。我可以在项目中添加一个新项目“Select One”,但“Select One”也会作为第一项显示在下拉列表中,这不是我想要的。
我该如何解决这个问题?
我试过的方法如下。取一个按钮并将单击事件赋予它。通过改变按钮背景,它似乎是一个旋转器。
声明为全局变量alertdialog和默认值..
AlertDialog d;
static int default_value = 0;
final Button btn = (Button) findViewById(R.id.button1);
btn .setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
//c.show();
final CharSequence str[] = {"Android","Black Berry","Iphone"};
AlertDialog.Builder builder =
new AlertDialog.Builder(TestGalleryActivity.this).setSingleChoiceItems(
str, default_value,new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int position)
{
Toast.makeText(TestGalleryActivity.this,
"" + position,
Toast.LENGTH_SHORT).show();
default_value = position;
btn.setText(str[position]);
if(d.isShowing())
d.dismiss();
}
}).setTitle("Select Any");
d = builder.create();
d.show();
}
});
我最终使用了Button。虽然Button不是旋转器,但其行为很容易自定义。
首先像往常一样创建适配器:
String[] items = new String[] {"One", "Two", "Three"};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_dropdown_item, items);
注意,我使用simple_spinner_dropdown_item作为布局id。这将有助于创建一个更好的外观时,创建警报对话框。
在onClick处理我的按钮,我有:
public void onClick(View w) {
new AlertDialog.Builder(this)
.setTitle("the prompt")
.setAdapter(adapter, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// TODO: user specific action
dialog.dismiss();
}
}).create().show();
}
就是这样!
对此,我找到了很多好的解决方案。大多数是通过在适配器的末尾添加一个项来工作的,并且不在下拉列表中显示最后一个项。
对我来说最大的问题是旋转器下拉列表将从列表的底部开始。所以用户看到的最后一个项目,而不是第一个项目(在情况下有许多项目显示),触摸转轮后,第一次。
所以我把提示项放在列表的开头。并在下拉列表中隐藏第一项。
private void loadSpinner(){
HintArrayAdapter hintAdapter = new HintArrayAdapter<String>(context, 0);
hintAdapter.add("Hint to be displayed");
hintAdapter.add("Item 1");
hintAdapter.add("Item 2");
.
.
hintAdapter.add("Item 30");
spinner1.setAdapter(hintAdapter);
//spinner1.setSelection(0); //display hint. Actually you can ignore it, because the default is already 0
//spinner1.setSelection(0, false); //use this if don't want to onItemClick called for the hint
spinner1.setOnItemSelectedListener(yourListener);
}
private class HintArrayAdapter<T> extends ArrayAdapter<T> {
Context mContext;
public HintArrayAdapter(Context context, int resource) {
super(context, resource);
this.mContext = context
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(android.R.layout.simple_spinner_item, parent, false);
TextView texview = (TextView) view.findViewById(android.R.id.text1);
if(position == 0) {
texview.setText("");
texview.setHint(getItem(position).toString()); //"Hint to be displayed"
} else {
texview.setText(getItem(position).toString());
}
return view;
}
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
View view;
if(position == 0){
view = inflater.inflate(R.layout.spinner_hint_list_item_layout, parent, false); // Hide first row
} else {
view = inflater.inflate(android.R.layout.simple_spinner_dropdown_item, parent, false);
TextView texview = (TextView) view.findViewById(android.R.id.text1);
texview.setText(getItem(position).toString());
}
return view;
}
}
在@Override getDropDownView()中设置下面的布局,当position为0时,隐藏第一个提示行。
R.layout.spinner_hint_list_item_layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
</LinearLayout>
When extending SpinnerAdapter, you override two View-producing methods, getView(int, View, ViewGroup) and getDropDownView(int, View, ViewGroup). The first one supplies the View inserted into the Spinner itself; the second supplies the View in the drop-down list (as the name suggests). You can override the getView(...) so that, until an item has been selected, it displays a TextView containing a prompt; then, when you detect an item has been selected, you change it to display a TextView corresponding to that.
public class PromptingAdapter extends SpinnerAdapter {
//... various code ...
private boolean selectionmade = false;
//call this method from the OnItemSelectedListener for your Spinner
public setSelectionState(boolean b) {
selectionmade = b;
}
@Override
public View getView(int position, View recycle, ViewGroup container) {
if(selectionmade) {
//your existing code to supply a View for the Spinner
//you could even put "return getDropDownView(position, recycle, container);"
}
else {
View output;
if(recycle instanceof TextView) {
output = recycle;
}
else {
output = new TextView();
//and layout stuff
}
output.setText(R.string.please_select_one);
//put a string "please_select_one" in res/values/strings.xml
return output;
}
}
//...
}