类型不匹配：不能从AsyncTask的转换 [英] Type mismatch: cannot convert from AsyncTask
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问题描述
基于@汤姆解决方案更新：
SongsManager.java
公共类SongsManager扩展的AsyncTask＆LT;无效，无效的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;＆GT; { 公共接口SongsMasterCallback {
无效showSongList（列表＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;结果）;
} 私人SongsMasterCallback mCallback;
公共SongsManager（SongsMasterCallback回调）
{
mCallback =回调;
} //构造
//公共SongsManager（）{}
ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT; songsList =新的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;（）;
@覆盖
保护的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT; doInBackground（虚空...... PARAMS）
{
//填充所有数据....
HashMap的＆LT;字符串，字符串＆GT;地图=新的HashMap＆LT;字符串，字符串＆GT;（）;
// .........
songsList.add（地图）;
} 返回songsList;
} @覆盖
保护无效onPostExecute（ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;的结果）{
// TODO自动生成方法存根
//super.onPostExecute(result）;
mCallback.showSongList（结果）;
}
}
main.java
公共类主要活动扩展实现SongsMasterCallback {公共无效showSongList（列表＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;结果）
{
this.songsList =（ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;）的结果;
//然后做一些与此列表
}@覆盖
公共无效的onCreate（捆绑savedInstanceState）{ 新SongsManager（本）.execute（）;
Log.d（songsSize，字符串：+ songsList.size（））; //它显示0？}}
更新结束
我使用的AsyncTask及以下一类的工作是，当我尝试执行我所获得
的下面是类：
SongManager.java
公共类SongsManager扩展的AsyncTask＆LT;无效，无效的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;＆GT; {
//构造
公共SongsManager（）{}
@覆盖
保护的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT; doInBackground（虚空...... PARAMS）{
// TODO自动生成方法存根 ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT; songsList =新的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;（）; Xml_Parser_Custom_Listview分析器=新Xml_Parser_Custom_Listview（）;
字符串XML = parser.getXmlFromUrl（URL）; // URL从XML获得
文档的文档= parser.getDomElement（XML）; //获得DOM元素 节点列表NL = doc.getElementsByTagName（KEY_NAME）;
//遍历所有歌曲节点＆LT循环;宋＆GT;
的for（int i = 0; I＆LT; nl.getLength（）;我++）{
//创建新的HashMap
HashMap的＆LT;字符串，字符串＆GT;地图=新的HashMap＆LT;字符串，字符串＆GT;（）;
元素e =（元）nl.item（I）
//将每个子节点的HashMap键=＆GT;值
//添加入行到地图... //添加HashList到ArrayList的
songsList.add（地图）;
} 返回songsList;
}
}
main.java文件
试图执行的AsyncTask的：
公开的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT; songsList =新的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;（）;
songsList =新SongsManager（）执行（）;
这里是错误：
类型不匹配：不能从AsyncTask的＆LT转换;无效，无效的ArrayList＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;＆GT;到ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;
解决方案
从返回的值SongsManager.execute（）不是计算的结果;它的的AsyncTask 本身。要发布你的结果，写的方法 SongsManager ：
无效onPostExecute（ArrayList的＆LT;＆HashMap的LT;字符串，字符串＆GT;＆GT;的结果）{
songsList =结果; //或者类似的东西
//然后更新UI以反映结果
}
在此方法中， songsList 是变量，你正试图从分配新SongsManager.execute（）。如果这个变量不是在 SongsManager 类（比如，它不是一个嵌套类主类的）可见，那么你就必须为回拨安排：
公共类SongsManager
延伸AsyncTask的＆LT;太虚，太虚，列表与LT;地图＆LT;字符串，字符串＆GT;＆GT;
{
公共接口SongsMasterCallback {
无效showSongList（列表＆LT;地图＆LT;字符串，字符串＆GT;＆GT;结果）;
} 私人SongsMasterCallback mCallback; 公共SongsMaster（SongsMasterCallback回调）{
mCallback =回调;
} @覆盖
保护列表与LT;地图＆LT;字符串，字符串＆GT;＆GT; doInBackground（虚空...... PARAMS）{
// 像之前一样
} @覆盖
保护无效onPostExecute（列表＆LT;地图＆LT;字符串，字符串＆GT;＆GT;的结果）{
mCallback.showSongList（结果）;
}
}
然后声明您的活动实施SongsManager.SongsManagerCallback 并添加方法是：
无效showSongList（列表＆LT;地图＆LT;字符串，字符串＆GT;＆GT;的SongList）{
this.songList =的SongList;
//然后做一些与此列表
}
Update based on @Tom solution:
SongsManager.java
public class SongsManager extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>> {
public interface SongsMasterCallback {
void showSongList(List<HashMap<String, String>> result);
}
private SongsMasterCallback mCallback;
public SongsManager (SongsMasterCallback callback)
{
mCallback = callback;
}
// Constructor
//public SongsManager(){ }
ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
@Override
protected ArrayList<HashMap<String, String>> doInBackground(Void... params)
{
//populating all the data....
HashMap<String, String> map = new HashMap<String, String>();
//.........
songsList.add(map);
}
return songsList;
}
@Override
protected void onPostExecute(ArrayList<HashMap<String, String>> result) {
// TODO Auto-generated method stub
//super.onPostExecute(result);
mCallback.showSongList(result);
}
}
main.java
public class Main extends Activity implements SongsMasterCallback {
public void showSongList(List<HashMap<String, String>> result)
{
this.songsList = (ArrayList<HashMap<String, String>>) result;
// then do something with the list here
}
@Override
public void onCreate(Bundle savedInstanceState) {
new SongsManager(this).execute();
Log.d("songsSize", "string : "+songsList.size()); //it shows 0 ???
}
}
end of update
I am working on a class using AsyncTask and below is what i am getting when i try to execute
the error is on the design time so there is no LogCat
here is the class:
SongManager.java
public class SongsManager extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>> {
// Constructor
public SongsManager(){ }
@Override
protected ArrayList<HashMap<String, String>> doInBackground(Void... params) {
// TODO Auto-generated method stub
ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
Xml_Parser_Custom_Listview parser = new Xml_Parser_Custom_Listview();
String xml = parser.getXmlFromUrl(URL); // getting XML from URL
Document doc = parser.getDomElement(xml); // getting DOM element
NodeList nl = doc.getElementsByTagName(KEY_NAME);
// 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
//adding the rows into to the map...
// adding HashList to ArrayList
songsList.add(map);
}
return songsList;
}
}
main.java file
trying to execute the AsyncTask:
public ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
songsList = new SongsManager().execute();
here is the error:
Type mismatch: cannot convert from AsyncTask<Void,Void,ArrayList<HashMap<String,String>>> to ArrayList<HashMap<String,String>>
解决方案
The value returned from SongsManager.execute() is not the results of the computation; it's the AsyncTask itself. To publish your results, write a method in SongsManager:
void onPostExecute(ArrayList<HashMap<String,String>> result) {
songsList = result; // or something similar
// then update the UI to reflect the results
}
In this method, songsList is the variable to which you are now trying to assign the return value from new SongsManager.execute(). If this variable is not visible to the SongsManager class (e.g., it's not a nested class of your main class), then you'll have to arrange for a call-back:
public class SongsManager
extends AsyncTask<Void, Void, List<Map<String,String>>
{
public interface SongsMasterCallback {
void showSongList(List<Map<String, String>> result);
}
private SongsMasterCallback mCallback;
public SongsMaster(SongsMasterCallback callback) {
mCallback = callback;
}
@Override
protected List<Map<String, String>> doInBackground(Void... params) {
// as before
}
@Override
protected void onPostExecute(List<Map<String, String>> result) {
mCallback.showSongList(result);
}
}
Then declare your activity to implement SongsManager.SongsManagerCallback and add is method:
void showSongList(List<Map<String, String>> songList) {
this.songList = songList;
// then do something with the list here
}
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