由于我对Android中的这个“异步任务”概念不熟悉，我搜索了很多帖子并实现了。在我的应用程序when opening the application i am fetching lot of images from url,中，所以它的delaying开了很多。所以我有打开应用程序时有一个活动的想法。我试过以下内容：
我的活动代码：
Gallery glly;
public void onCreate(Bundle savedInstanceState)
{
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
super.onCreate(savedInstanceState);
setContentView(R.layout.galleryview);
new RestoreDBTask().execute();
}
class RestoreDBTask extends AsyncTask <Void, Void, Nodelist>
{
private ProgressDialog dialog;
Context ctx;
public RestoreDBTask( Context ctx) {
this.ctx = ctx;
}
@Override
protected void onPreExecute()
{
dialog = ProgressDialog.show(
ctx,"Please Wait","Loading...", true);
}
@Override
protected Nodelist doInBackground(Void... params)
{
final String URLHeading = "http://m.indiatoday.in/xml/stories/sections_listing.xml";
Heading parser = new Heading();
String xmldata = parser.getXmlFromUrl(URLHeading);
Document domelement = parser.getDomElement(xmldata);
NodeList node = domelement.getElementsByTagName("item");
context.getInstance().setAppVariable("flag", "Home");
adapter=new GalleryviewAdapter(NewspapperActivity.this);
// GalleryviewAdapter adapter= new GalleryviewAdapter();
adapter.getelement("http://m.bvdjujd.in/xml/stories/jusdjhs.xml",1);
return node;
}
@Override
protected void onPostExecute(String result)
{
Element e0 = (Element) node.item(0);
txt1.setText(parser.getValue(e0, "sectionname"));
Element e1 = (Element) node.item(1);
txt2.setText(parser.getValue(e1, "sectionname"));
Element e2 = (Element) node.item(2);
txt3.setText(parser.getValue(e2, "sectionname"));
Element e3 = (Element) node.item(3);
txt4.setText(parser.getValue(e3, "sectionname"));
Element e4 = (Element) node.item(4);
txt5.setText(parser.getValue(e4, "sectionname"));
glly.setAdapter(adapter);
DisplayMetrics metrics1 = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics1);
MarginLayoutParams mlp1 = (MarginLayoutParams) glly.getLayoutParams();
mlp1.setMargins(-(metrics1.widthPixels/2+40),mlp1.topMargin,mlp1.rightMargin, mlp1.bottomMargin );
dialog.dismiss();
}
}
我的logcat：
03-12 10:24:08.430: I/Process(487): Sending signal. PID: 487 SIG: 9
03-12 10:24:22.140: D/dalvikvm(511): GC freed 2643 objects / 197184 bytes in 168ms
03-12 10:24:24.800: I/MemoryCache(511): MemoryCache will use up to 6.0MB
03-12 10:24:24.810: W/dalvikvm(511): threadid=15: thread exiting with uncaught exception (group=0x4001b188)
03-12 10:24:24.845: E/AndroidRuntime(511): Uncaught handler: thread AsyncTask #1 exiting due to uncaught exception
03-12 10:24:24.932: E/AndroidRuntime(511): java.lang.RuntimeException: An error occured while executing doInBackground()
03-12 10:24:24.932: E/AndroidRuntime(511): at android.os.AsyncTask$3.done(AsyncTask.java:200)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.lang.Thread.run(Thread.java:1096)
03-12 10:24:24.932: E/AndroidRuntime(511): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
03-12 10:24:24.932: E/AndroidRuntime(511): at android.os.Handler.<init>(Handler.java:121)
03-12 10:24:24.932: E/AndroidRuntime(511): at com.newspapper.ImageLoader.<init>(ImageLoader.java:29)
03-12 10:24:24.932: E/AndroidRuntime(511): at com.newspapper.GalleryviewAdapter.<init>(GalleryviewAdapter.java:52)
03-12 10:24:24.932: E/AndroidRuntime(511): at com.newspapper.NewspapperActivity$RestoreDBTask.doInBackground(NewspapperActivity.java:569)
03-12 10:24:24.932: E/AndroidRuntime(511): at com.newspapper.NewspapperActivity$RestoreDBTask.doInBackground(NewspapperActivity.java:1)
03-12 10:24:24.932: E/AndroidRuntime(511): at android.os.AsyncTask$2.call(AsyncTask.java:185)
03-12 10:24:24.932: E/AndroidRuntime(511): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
03-12 10:24:24.932: E/AndroidRuntime(511): ... 4 more
03-12 10:24:25.000: I/dalvikvm(511): threadid=7: reacting to signal 3
03-12 10:24:25.214: I/dalvikvm(511): Wrote stack trace to '/data/anr/traces.txt'
请帮我解决这个问题。请帮助我，不管我是否采取正确的行动......谢谢提前..
答案 0 :(得分：2)
对于RestoreDBTask类型
，方法findViewById（int）未定义
因为您正在尝试从RestoreDBTask类访问UI元素。您可以使用Activity上下文而不是RestoreDBTask解决此问题：
TextView txt1 = (TextView)Your_Activity_Name.this.findViewById(R.id.Text01);
TextView txt2 = (TextView)Your_Activity_Name.this.findViewById(R.id.Text02);
TextView txt3 = (TextView)Your_Activity_Name.this.findViewById(R.id.Text03);
//....
但是当您尝试运行当前应用时，您将收到以下错误：
alledFromWrongThreadException：只创建了一个原始线程 视图层次结构可以触及其视图。
要避免在Streps后出现此错误：
1。首先从doInBackground内的网络服务获取数据。
2。从NodeList node方法
doInBackground
3. 最终在onPostExecute中获取NodeList并执行xml解析然后访问或更新UI元素
示例： -
class RestoreDBTask extends AsyncTask <Void, Void, NodeList>
{
///.. your code here.....
@Override
protected NodeList doInBackground(Void... params)
{
//....your code here..
return node;
}
@Override
protected void onPostExecute(NodeList result)
{
// get data from result
....
// access UI elements here add value to it
TextView txt1 = (TextView)Your_Activity_Name.
this.findViewById(R.id.Text01);
TextView txt2 = (TextView)Your_Activity_Name.
this.findViewById(R.id.Text02);
......
dialog.dismiss();
}
}