我搜索了其他帖子，但没有找到任何描述我的特定问题的帖子。其中许多是指从 doInBackground 调用 publishProgress。我正在从 onPreExecute 调用 publishProgress，期望显示一个对话框以通知用户正在获取数据。AsyncTask 正在从用户从 Spinner 中进行选择启动。UI 不会显示对话框，而是冻结直到 AsyncTask 完成。我已在日志消息中添加，看起来虽然在 onPreExecute 中调用了 publishProgress，但直到 doInBackground 完成后才会执行 onProgressUpdate。
活动：
public class MainActivity extends Activity implements OnItemSelectedListener{
private Spinner spinner;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
protected void onResume() {
super.onResume();
spinner = (Spinner)findViewById(R.id.spinner);
SpinnerAdapter adapter = new CustomSpinnerAdapter<String>(this, new String[]{"one", "two", "three"});
spinner.setAdapter(adapter);
spinner.setOnItemSelectedListener(this);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@SuppressLint("NewApi")
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
try{
FetchDataTask fetchDataTask = new FetchDataTask();
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB){
fetchDataTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, "data");
} else{
fetchDataTask.execute("data");
}
fetchDataTask.await();
} catch (InterruptedException e){
e.printStackTrace();
}
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
public class FetchDataTask extends AsyncTask<String, Integer, Boolean> {
private final String TAG = FetchDataTask.class.getSimpleName();
private final Integer FETCHING_DATA = 1;
CountDownLatch countDownLatch = new CountDownLatch(1);
ProgressDialog dialog;
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
Log.d(TAG,"Exiting onPostExecute");
dialog.dismiss();
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
publishProgress(FETCHING_DATA);
Log.d(TAG, "Exiting onPreExecute");
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
dialog = ProgressDialog.show(MainActivity.this, "Fetching", "Data");
Log.d(TAG, "Exiting onProgressUpdate");
}
@Override
protected Boolean doInBackground(String... arg0) {
/*
* Fetching data here
*/
Log.d(TAG, "Exiting doInBackground");
countDownLatch.countDown();
return true;
}
public void await() throws InterruptedException{
countDownLatch.await();
}
}
}
微调器：
public class CustomSpinnerAdapter<T> implements SpinnerAdapter {
Context context;
T[] values;
public CustomSpinnerAdapter(Context context, T[] values){
this.context = context;
this.values = values;
for(T value: this.values){
Log.d("Spinner", value.toString());
}
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return values.length;
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return values[position];
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public int getItemViewType(int position) {
// TODO Auto-generated method stub
return android.R.layout.simple_spinner_dropdown_item;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
TextView v = new TextView(context);
v.setTextColor(Color.BLACK);
v.setText(values[position].toString());
return v;
}
@Override
public int getViewTypeCount() {
// TODO Auto-generated method stub
return 1;
}
@Override
public boolean hasStableIds() {
// TODO Auto-generated method stub
return false;
}
@Override
public boolean isEmpty() {
// TODO Auto-generated method stub
return false;
}
@Override
public void registerDataSetObserver(DataSetObserver observer) {
// TODO Auto-generated method stub
}
@Override
public void unregisterDataSetObserver(DataSetObserver observer) {
// TODO Auto-generated method stub
}
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
return this.getView(position, convertView, parent);
}
}
风景：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<Spinner
android:id="@+id/spinner"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</RelativeLayout>
我认为这可能与从 Spinner 选择中执行 AsyncTask 有关，因为只需在 Activity 中执行它而不将其连接到 Spinner 就没有这个问题。任何援助将不胜感激。