我正在建立歌曲列表应用程序。我想在加载数据时显示启动画面。为此，我设置了一个AsyncTask与ViewSwitcher相结合来切换启动画面（只是徽标和圆形进度条）和主屏幕之间的xml布局。问题是当在ListView中放置数据时，我使用的是BaseAdapter，它位于单独的类中，并抛出错误"The Constructor LazyAdapter(Home.LoadViewTask, ArrayList<HashMap<String,String>>) is undefined"。
这是具有AsyncTask的Home Class的源代码：
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.main);
mBtnNaslovnica = (Button) findViewById(R.id.mBtnNaslovnica);
mBtnNaslovnica.setSelected(true);
new LoadViewTask().execute();
}
//To use the AsyncTask, it must be subclassed
public class LoadViewTask extends AsyncTask<Void, Integer, Void>
{
//A TextView object and a ProgressBar object
private TextView tv_progress;
private ProgressBar pb_progressBar;
//Before running code in the separate thread
@Override
protected void onPreExecute()
{
//Initialize the ViewSwitcher object
viewSwitcher = new ViewSwitcher(Home.this);
/* Initialize the loading screen with data from the 'loadingscreen.xml' layout xml file.
* Add the initialized View to the viewSwitcher.*/
viewSwitcher.addView(ViewSwitcher.inflate(Home.this, R.layout.init, null));
//Set ViewSwitcher instance as the current View.
setContentView(viewSwitcher);
}
//The code to be executed in a background thread.
@Override
protected Void doInBackground(Void... params)
{
ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
XMLParser parser = new XMLParser();
String xml = parser.getXmlFromUrl(URL); // getting XML from URL
Document doc = parser.getDomElement(xml); // getting DOM element
NodeList nl = doc.getElementsByTagName(KEY_SONG);
// looping through all song nodes <song>
for (int i = 0; i < nl.getLength(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
// adding each child node to HashMap key => value
map.put(KEY_ID, parser.getValue(e, KEY_ID));
map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));
// adding HashList to ArrayList
songsList.add(map);
}
list=(ListView)findViewById(R.id.list);
// Getting adapter by passing xml data ArrayList
adapter=new LazyAdapter(this, songsList);
list.setAdapter(adapter);
// Click event for single list row
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
}
});
return null;
}
//After executing the code in the thread
@Override
protected void onPostExecute(Void result)
{
/* Initialize the application's main interface from the 'main.xml' layout xml file.
* Add the initialized View to the viewSwitcher.*/
viewSwitcher.addView(ViewSwitcher.inflate(Home.this, R.layout.main, null));
//Switch the Views
viewSwitcher.showNext();
}
}
//Override the default back key behavior
@Override
public void onBackPressed()
{
//Emulate the progressDialog.setCancelable(false) behavior
//If the first view is being shown
if(viewSwitcher.getDisplayedChild() == 0)
{
//Do nothing
return;
}
else
{
//Finishes the current Activity
super.onBackPressed();
}
}
这是LazyAdapter类的来源：
private Activity activity;
private ArrayList<HashMap<String, String>> data;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;
public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return data.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.list_row, null);
TextView title = (TextView)vi.findViewById(R.id.title); // title
TextView artist = (TextView)vi.findViewById(R.id.artist); // artist name
TextView duration = (TextView)vi.findViewById(R.id.duration); // duration
ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image
HashMap<String, String> song = new HashMap<String, String>();
song = data.get(position);
// Setting all values in listview
title.setText(song.get(Home.KEY_TITLE));
artist.setText(song.get(Home.KEY_ARTIST));
duration.setText(song.get(Home.KEY_DURATION));
imageLoader.DisplayImage(song.get(Home.KEY_THUMB_URL), thumb_image);
return vi;
}
`
答案 0 :(得分：1)
你的构造函数在第一个参数get Activity中传递了LoadViewTask的实例（这引用了当前的LoadViewTask实例）， 而不是这个用途：
adapter = new LazyAdapter（Home.this，songsList）;
主页应该是您活动的名称
答案 1 :(得分：1)
您无法进行任何UI修改...例如设置标签文本，修改AsyncTask.doInBackground中的列表..因为它是一个单独的线程......
list=(ListView)findViewById(R.id.list);
// Getting adapter by passing xml data ArrayList
adapter=new LazyAdapter(this, songsList);
list.setAdapter(adapter);
// Click event for single list row
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
}
});
在调用
之前，你应该把这部分代码放进去new LoadViewTask（）。execute（）;
并在doInBackground（）中...作为最后一行.. 把这条线.. adapter.notifyDataSetChanged（）;
答案 2 :(得分：0)
问题在于，无论出于何种原因，您需要Activity作为构造函数的第一个参数。通过将this传递给适配器的构造函数，您传递的是AsyncTask类型的对象，该对象不是活动且没有上下文。因此，您应该在Activity的重写构造函数中传递LoadViewTask作为参数，然后将其用作构造函数的正确参数。
但是，在将上下文绑定到AsyncTask时要小心，因为它可能会导致意外行为（Activity尝试更新时AsyncTask可能不再存在。 AsyncTask是一个非常危险的类，因为它有许多与同步相关的缺陷。
答案 3 :(得分：0)
我希望这可能有所帮助，
onPostExecute include (Inside AsyncTask)
ExampleAdapter sectionedAdapter = new EfficientAdapter(ClassInfoThread.this,getBaseContext());
listView.setAdapter(sectionedAdapter);
并在您的适配器类中添加此构造函数
public ExampleAdapter(ExampleThread exampleThread,Context context) {
// TODO Auto-generated constructor stub`enter code here`
mInflater = LayoutInflater.from(context);
}