Android 我如何让我的doInBackground方法起作用?
我的错误消息是:Android 我如何让我的doInBackground方法起作用?,android,asynchronous,task,Android,Asynchronous,Task,我的错误消息是: >02-12 10:15:34.625: E/AndroidRuntime(1018): FATAL EXCEPTION: AsyncTask > 1 02-12 10:15:34.625: E/AndroidRuntime(1018): java.lang.RuntimeException: An error occured while executing > doInBackground() 02-12 10:15:34.625: E/AndroidRun
>02-12 10:15:34.625: E/AndroidRuntime(1018): FATAL EXCEPTION: AsyncTask
> 1 02-12 10:15:34.625: E/AndroidRuntime(1018): java.lang.RuntimeException: An error occured while executing
> doInBackground() 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> android.os.AsyncTask$3.done(AsyncTask.java:200) 02-12 10:15:34.625:
> E/AndroidRuntime(1018): at
> java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> java.util.concurrent.FutureTask.setException(FutureTask.java:124)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> java.util.concurrent.FutureTask.run(FutureTask.java:137) 02-12
> 10:15:34.625: E/AndroidRuntime(1018): at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> java.lang.Thread.run(Thread.java:1096) 02-12 10:15:34.625:
> E/AndroidRuntime(1018): Caused by: java.lang.NullPointerException
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> se.gibk.gibk.MainActivity$PostTask.GetList(MainActivity.java:88) 02-12
> 10:15:34.625: E/AndroidRuntime(1018): at
> se.gibk.gibk.MainActivity$PostTask.doInBackground(MainActivity.java:143)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> se.gibk.gibk.MainActivity$PostTask.doInBackground(MainActivity.java:1)
> 02-12 10:15:34.625: E/AndroidRuntime(1018): at
> android.os.AsyncTask$2.call(AsyncTask.java:185) 02-12 10:15:34.625:
> E/AndroidRuntime(1018): at
> java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
我的代码是:
public class MainActivity extends Activity {
private static final String TAG = "Debugging";
private ListView list;
ArrayList<String> links;
Sermons sermons;
protected void onCreate(Bundle savedInstanceState) {
Log.d(TAG, "MainActivity - OnCreate()");
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new PostTask(this).execute("http://gibk.se/sample-page/predikningar/?podcast");
Log.d(TAG, "execute");
}
公共类MainActivity扩展活动{
私有静态最终字符串标记=“调试”;
私有列表视图列表;
ArrayList链接;
布道;
创建时受保护的void(Bundle savedInstanceState){
d(标记“MainActivity-OnCreate()”);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
新建PostTask(此)。执行(“http://gibk.se/sample-page/predikningar/?podcast");
Log.d(标记“执行”);
}
公共类PostTask扩展AsyncTask>{
private Context context;
public PostTask(Context context) {
this.context = context;
}
private ArrayList<Sermons> GetList(String url) {
Log.d(TAG, "GetList");
ArrayList<Sermons> results = new ArrayList<Sermons>();
try {
URL urls = new URL(url);
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(false);
XmlPullParser xmlParser = factory.newPullParser();
xmlParser.setInput(this.getInputStream(urls), "UTF_8");
boolean insideItem = false;
int eventType = xmlParser.getEventType();
while (eventType != XmlPullParser.END_DOCUMENT) {
if (eventType == XmlPullParser.START_TAG) {
if (xmlParser.getName().equalsIgnoreCase("item")) {
sermons = new Sermons();
insideItem = true;
} else if (xmlParser.getName().equalsIgnoreCase("title")) {
if (insideItem)
sermons.setSermon(xmlParser.nextText());
} else if (xmlParser.getName().equalsIgnoreCase("itunes:author")) {
if (insideItem)
sermons.setPreacher(xmlParser.nextText());
} else if (xmlParser.getName().equalsIgnoreCase("guid")) {
if (insideItem)
links.add(xmlParser.nextText());
}
results.add(sermons);
}
else if(eventType==XmlPullParser.END_TAG && xmlParser.getName().equalsIgnoreCase("item")){
insideItem=false;
}
eventType = xmlParser.next();
}
}
catch (MalformedURLException e) {
e.printStackTrace();
}
catch (XmlPullParserException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
return results;
}
private InputStream getInputStream(URL url) {
try {
return url.openConnection().getInputStream();
} catch (IOException e) {
return null;
}
}
@Override
protected ArrayList<Sermons> doInBackground(String... params) {
Log.d(TAG, "doInBackGround");
String url = params[0];
ArrayList<Sermons> sermon = this.GetList(url);
return sermon;
}
@Override
protected void onPostExecute(ArrayList<Sermons> result) {
super.onPostExecute(result);
Log.d(TAG, "onPostExecute");
links = new ArrayList<String>();
list = (ListView) findViewById(R.id.list);
list.setAdapter(new Adapter(MainActivity.this, (ArrayList<Sermons>) result));
list.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View v, int position,
long arg3) {
Uri uri = Uri.parse(links.get(position));
String url = uri.toString();
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setData(Uri.parse(url));
startActivity(intent);
}
});
}
私有上下文;
公共PostTask(上下文){
this.context=上下文;
}
私有ArrayList GetList(字符串url){
Log.d(标签“GetList”);
ArrayList结果=新建ArrayList();
试一试{
URL URL=新URL(URL);
XmlPullParserFactory工厂=XmlPullParserFactory.newInstance();
factory.setNamespaceAware(false);
XmlPullParser xmlParser=factory.newPullParser();
setInput(这个.getInputStream(URL),“UTF_8”);
布尔值insideItem=false;
int eventType=xmlParser.getEventType();
while(eventType!=XmlPullParser.END_文档){
if(eventType==XmlPullParser.START_标记){
if(xmlParser.getName().equalsIgnoreCase(“项”)){
布道=新布道();
insideItem=真;
}else if(xmlParser.getName().equalsIgnoreCase(“title”)){
如果(内部项目)
setSermon(xmlParser.nextText());
}else if(xmlParser.getName().equalsIgnoreCase(“itunes:author”)){
如果(内部项目)
布道者(xmlParser.nextText());
}else if(xmlParser.getName().equalsIgnoreCase(“guid”)){
如果(内部项目)
add(xmlParser.nextText());
}
结果:添加(布道);
}
else if(eventType==XmlPullParser.END_标记&&xmlParser.getName().equalsIgnoreCase(“项”)){
insideItem=假;
}
eventType=xmlParser.next();
}
}
捕获(格式错误){
e、 printStackTrace();
}
catch(XMLPullParseRexE){
e、 printStackTrace();
}
捕获(IOE异常){
e、 printStackTrace();
}
返回结果;
}
私有InputStream getInputStream(URL){
试一试{
返回url.openConnection().getInputStream();
}捕获(IOE异常){
返回null;
}
}
@凌驾
受保护的ArrayList doInBackground(字符串…参数){
Log.d(标签“doInBackGround”);
字符串url=params[0];
ArrayList布道=this.GetList(url);
回教;
}
@凌驾
受保护的void onPostExecute(ArrayList结果){
super.onPostExecute(结果);
Log.d(标记“onPostExecute”);
links=newarraylist();
list=(ListView)findViewById(R.id.list);
list.setAdapter(新适配器(MainActivity.this,(ArrayList)结果));
list.setOnItemClickListener(新的OnItemClickListener(){
@凌驾
公共视图单击(AdapterView arg0,视图v,内部位置,
长arg3){
Uri=Uri.parse(links.get(position));
字符串url=uri.toString();
意向意向=新意向(意向.行动\视图);
setData(Uri.parse(url));
星触觉(意向);
}
});
}
}
}不确定其是否相关,但:
"title".equalsIgnoreCase(xmlParser.getName())
优于:
xmlParser.getName().equalsIgnoreCase("title")
减少NPE的机会
另一个问题:
private InputStream getInputStream(URL url) {
try {
return url.openConnection().getInputStream();
} catch (IOException e) {
return null;
}
}
异常时不应返回null,而应抛出异常。在getList函数中获得NPE。是的,我知道,但当我调试解析方法时,不会添加值,因此doinbackground返回null。为什么我不知道,因为我的解析正在我的另一个项目中工作。你能调试并检查getList函数中的空值吗?调试时的问题是它从未进入布道;因此它给出了一个空值。这是wierd,因为我在没有syncTask的其他项目中使用了相同的代码,然后它就工作了?