[英]Android - return value from thread
我有一个从资源检索图像并将其显示在GridView
。 一切都可以正常工作,但是由于性能问题,我想在运行时创建拇指,因此我创建了一个新的ProgressDialog
来告知用户该应用程序正在运行:
import java.util.ArrayList;
import android.app.Fragment;
import android.app.ProgressDialog;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.InflateException;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.GridView;
import com.italiandevteam.chuck.adapter.GridViewAdapter;
import com.italiandevteam.chuck.model.ImageItem;
public class GalleriaPersonaggio extends Fragment{
Integer personaggio = null;
private ProgressDialog progressDialog;
TypedArray imgs = null;
final ArrayList imageItems = new ArrayList();
public GalleriaPersonaggio( int personaggio ){
this.personaggio = personaggio;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
int id = getIdPersonaggio();
View rootView = null;
try {
rootView = inflater.inflate(R.layout.gallery_grid, container, false);
}
catch (InflateException e) {
}
final GridView gridView = (GridView) rootView.findViewById(R.id.gridView);
GridViewAdapter customGridAdapter = new GridViewAdapter(getActivity(), R.layout.gallery_row, getData(personaggio));
gridView.setAdapter(customGridAdapter);
gridView.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
// HashMap<String, Object> hm = gridView.getAdapter().getPosition(position);
//
// String imgPath = (String) hm.get("flag"); //get downloaded image path
// Intent i = new Intent(getActivity(), MostraImmagine.class); //start new Intent to another Activity.
// i.putExtra("ClickedImagePath", imgPath ); //put image link in intent.
// startActivity(i);
}
});
return rootView;
}
public int getIdPersonaggio(){
return this.personaggio;
}
private ArrayList getData(int personaggio) {
// retrieve String drawable array
switch( personaggio )
{
case 1:{
imgs = getResources().obtainTypedArray(R.array.chuck_ids);
break;
}
case 2:{
imgs = getResources().obtainTypedArray(R.array.sarah_ids);
break;
}
default:{
imgs = getResources().obtainTypedArray(R.array.chuck_ids);
}
}
final ProgressDialog ringProgressDialog = ProgressDialog.show(getActivity(), "Please wait ...", "Loading Images ...", true);
ringProgressDialog.setCancelable(true);
new Thread(new Runnable() {
@Override
public void run() {
try {
int THUMBNAIL_HEIGHT = 100;
int THUMBNAIL_WIGHT = 100;
for (int i = 0; i < imgs.length(); i++)
{
Bitmap bitmap = BitmapFactory.decodeResource(getActivity().getResources(), imgs.getResourceId(i, -1));
bitmap = Bitmap.createScaledBitmap(bitmap, THUMBNAIL_HEIGHT, THUMBNAIL_WIGHT, false);
// ByteArrayOutputStream baos = new ByteArrayOutputStream();
// bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);
// byte[] imageData = baos.toByteArray();
// InputStream is = new ByteArrayInputStream(imageData);
// Bitmap b = BitmapFactory.decodeStream(is);
imageItems.add(new ImageItem(bitmap, "Image#" + i));
}
} catch (Exception e) {
}
ringProgressDialog.dismiss();
}
}).start();
return imageItems;
}
}
问题是,最后代码没有返回任何内容, GridView
为空,如果我删除线程,它将很好地工作。
线程实例不能返回值,因为run方法的返回类型为void。 您可以做的是实现delegate
模式(Android中的监听器),或切换到Callable
接口和Executors
。 请注意,等待返回类型也没有什么意义。 如果您有以下事情:
伪代码UIThread:
variable = threadInstance.getResult();
您进行了异步调用,同步
正如323go所指出的,您可以使用AsyncTask (更好的IMHO)。 创建一个这样的内部类:
private class MyAsyncTask extends AsyncTask<ArrayList<String>, Integer, Long> {
...
}
Integer用于更新进度对话框(如果您不需要,请放Void代替); Long是DoInBackground方法的结果。 像这样启动您的AsyncTask:
new MyAsyncTask().execute(passing);
现在我不知道您的目标是什么,但是如果您遵循323go或本教程建议的链接,则可以改进代码。
编辑
在323go注释之后,最好在AsyncTask构造函数中传递对象的ArrayList:
new MyAsyncTask(passing).execute();
当然,在AsyncTask类中,您必须创建一个内部变量:
...
private ArrayList<Object> myArrayList;
private MyAsyncTask(ArrayList<Object> anArrayList) {
myArrayList = anArrayList;
}
...
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