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[英]Can not create handler inside thread that has not called Looper.prepare()
[英]How to overcome “Can't create handler inside thread that has not called Looper.prepare()” issue?
我正在尝试在viewpager中创建片段。 在适配器中,我使用线程来创建片段。 在线程内部,我正在执行AsyncTask,它进一步获取片段。 在每个片段类(OneFragment,TwoFragment)中,我都有AsyncTask,它们可以从Web访问一些API。 如果我根本不使用线程和AsyncTask,则该应用程序效果很好。 我正在使用它来提高UI性能。 但这是在获取错误。 我已经讨论了关于同一问题的一些已经存在的主题。 但是我不知道原因。 谁能指出我在这里做错了什么?
这是我的适配器类和AsyncTask类:
class SectionsPagerAdapter extends FragmentStatePagerAdapter {
Activity activity;
Fragment f = null;
public SectionsPagerAdapter(FragmentManager fm, Activity activity) {
super(fm);
this.activity = activity;
}
@Override
public Fragment getItem(int i) {
switch (i) {
case 0: {
activity.runOnUiThread(new Runnable() {
public void run() {
try {
f = new FetchFragment().execute("one").get();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
return f;
}
case 1: {
activity.runOnUiThread(new Runnable() {
public void run() {
try {
f = new FetchFragment().execute("two").get();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
return f;
}
}
return null;
}
@Override
public int getCount() {
return 2;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "one";
case 1:
return "two";
}
return null;
}
class FetchFragment extends AsyncTask<String, Void, Fragment>
{
@Override
protected Fragment doInBackground(String... arg0) {
if(arg0[0].equalsIgnoreCase("one"))
{
Fragment fragment = new OneFragment();
Bundle args = new Bundle();
args.putInt(CategoriesFragment.ARG_SECTION_NUMBER, 1);
fragment.setArguments(args);
return fragment;
}
if(arg0[0].equalsIgnoreCase("two"))
{
Fragment fragment = new TwoFragment();
Bundle args = new Bundle();
args.putInt(FeaturedFragment.ARG_SECTION_NUMBER, 2);
fragment.setArguments(args);
return fragment;
}
return null;
}
@Override
protected void onPostExecute(Fragment fragment){}
}
}
这是我的错误日志。
10-23 12:52:28.835: E/AndroidRuntime(17485): FATAL EXCEPTION: AsyncTask #3
10-23 12:52:28.835: E/AndroidRuntime(17485): java.lang.RuntimeException: An error occured while executing doInBackground()
10-23 12:52:28.835: E/AndroidRuntime(17485): at android.os.AsyncTask$3.done(AsyncTask.java:299)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-23 12:52:28.835: E/AndroidRuntime(17485): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.lang.Thread.run(Thread.java:856)
10-23 12:52:28.835: E/AndroidRuntime(17485): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
10-23 12:52:28.835: E/AndroidRuntime(17485): at android.os.Handler.<init>(Handler.java:121)
10-23 12:52:28.835: E/AndroidRuntime(17485): at android.support.v4.app.ListFragment.<init>(ListFragment.java:47)
10-23 12:52:28.835: E/AndroidRuntime(17485): at com.store.fragments.OneFragment.<init>(OneFragment.java:68)
10-23 12:52:28.835: E/AndroidRuntime(17485): at com.store.adapter.SectionsPagerAdapter$FetchFragment.doInBackground(SectionsPagerAdapter.java:173)
10-23 12:52:28.835: E/AndroidRuntime(17485): at com.store.adapter.SectionsPagerAdapter$FetchFragment.doInBackground(SectionsPagerAdapter.java:1)
10-23 12:52:28.835: E/AndroidRuntime(17485): at android.os.AsyncTask$2.call(AsyncTask.java:287)
10-23 12:52:28.835: E/AndroidRuntime(17485): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
好的,您使用asynctasks做错了。 通常,异步任务用于一些耗时的操作,这些操作应该在后台处理,但是您试图在UiThread上运行它。 并且在asynctask中,您尝试在doInBackground()中修改UI,但强烈建议在onPostExecute()中进行修改
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