如何在 AsyncTask 中加载 imageView

Question

我的应用程序中有 ViewPager，其中包含 7 个片段，每个片段包含多个图像。我想在每个片段加载它的图像时显示 ProgressBar。所以我创建了 AsyncTask 在后台加载图像。问题是我无法使用 Picasso 库加载图像，它显示了一些错误。谁能帮我想想怎么做？

编辑： 我问这个的原因是因为用 Picasso 加载所有图像需要大约 1.5 秒，而且看起来很慢。 "android:src" 应用程序有时会因为 OutOfMemory 问题而崩溃，"The application may be doing too much work on its main thread." 所以我正在寻找更好的方法。

谢谢！！！

fragment1.java:

public class Fragment1 extends Fragment {

public Fragment1() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, final ViewGroup container,
                         Bundle savedInstanceState) {

     View rootView = inflater.inflate(R.layout.fragment_frag1, container, false);

    LoadImagesTask loadImagesTask = new LoadImagesTask();
    loadImagesTask.execute();

                // Inflate the layout for this fragment
        return rootView;
}

private class LoadImagesTask extends AsyncTask<Void, Void, Void> {
        ProgressBar progressBar = (ProgressBar) getActivity().findViewById(R.id.loading);
        ImageView image1 = (ImageView) getActivity().findViewById(R.id.imageView_S0P1);
        ImageView image2 = (ImageView) getActivity().findViewById(R.id.imageView_S0P2);
        ImageView image3 = (ImageView) getActivity().findViewById(R.id.imageView_S0P3);
        ImageView image4 = (ImageView) getActivity().findViewById(R.id.imageView_S0P4);
        ImageView image5 = (ImageView) getActivity().findViewById(R.id.imageView_S0P5);
        ImageView image6 = (ImageView) getActivity().findViewById(R.id.imageView_S0P6);
        ImageView image7 = (ImageView) getActivity().findViewById(R.id.imageView_S0P7);
        ImageView image8 = (ImageView) getActivity().findViewById(R.id.imageView_S0P8);
        ImageView image9 = (ImageView) getActivity().findViewById(R.id.imageView_S0P9);
        ImageView image10 = (ImageView) getActivity().findViewById(R.id.imageView_S0P10);

    @Override
    protected Void doInBackground(Void... params) {

        getActivity().runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Picasso.with(getActivity()).load(R.drawable.s0p1).into(image1);
                Picasso.with(getActivity()).load(R.drawable.s0p2).into(image2);
                Picasso.with(getActivity()).load(R.drawable.s0p3).into(image3);
                Picasso.with(getActivity()).load(R.drawable.s0p4).into(image4);
                Picasso.with(getActivity()).load(R.drawable.s0p5).into(image5);
                Picasso.with(getActivity()).load(R.drawable.s0p6).into(image6);
                Picasso.with(getActivity()).load(R.drawable.s0p7).into(image7);
                Picasso.with(getActivity()).load(R.drawable.s0p8).into(image8);
                Picasso.with(getActivity()).load(R.drawable.s0p9).into(image9);
                Picasso.with(getActivity()).load(R.drawable.s0p10).into(image10);
            }
        });

        return null;
    }

    @Override
    protected void onPostExecute(Void event) {
        progressBar.setVisibility(View.GONE);
    }
}
}

Logcat:

07-12 17:03:32.838 17497-17581/appinventor.ai_itiel_maimon.Rubiks_cube E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
                                                                                     Process: appinventor.ai_itiel_maimon.Rubiks_cube, PID: 17497
                                                                                     java.lang.RuntimeException: An error occurred while executing doInBackground()
                                                                                         at android.os.AsyncTask.done(AsyncTask.java:309)
                                                                                         at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
                                                                                         at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
                                                                                         at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                                                                                         at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234)
                                                                                         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
                                                                                         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
                                                                                         at java.lang.Thread.run(Thread.java:818)
                                                                                      Caused by: java.lang.IllegalStateException: Method call should happen from the main thread.
                                                                                         at com.squareup.picasso.Utils.checkMain(Utils.java:136)
                                                                                         at com.squareup.picasso.RequestCreator.into(RequestCreator.java:615)
                                                                                         at com.squareup.picasso.RequestCreator.into(RequestCreator.java:601)
                                                                                         at appinventor.ai_itiel_maimon.Rubiks_cube.Intro$LoadImagesTask.doInBackground(Intro.java:68)
                                                                                         at appinventor.ai_itiel_maimon.Rubiks_cube.Intro$LoadImagesTask.doInBackground(Intro.java:36)
                                                                                         at android.os.AsyncTask.call(AsyncTask.java:295)
                                                                                         at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                                                                                         at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234) 
                                                                                         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
                                                                                         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
                                                                                         at java.lang.Thread.run(Thread.java:818)

Answer 1

AsyncTask 背后的想法是 doInBackground 执行后台工作，然后您可以 return 一些东西将作为参数传递给在主线程中执行的 onPostExecute。所以尝试从 onPostExecute() 方法设置图像 :) 但是你可以在不使用 AsyncTask 的情况下轻松地做到这一点，就像这样：

public class BlankFragment extends Fragment {


    private ImageView imv1;
    private ImageView imv2;
    private ImageView imv3;
    private ImageView imv4;
    private ImageView imv5;
    private ImageView imv6;
    private ImageView imv7;
    private ImageView imv8;
    private ImageView imv9;
    ProgressDialog progressDialog = null;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_blank, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        imv1 = (ImageView) getActivity().findViewById(R.id.imageView);
        imv2 = (ImageView) getActivity().findViewById(R.id.imageView2);
        imv3 = (ImageView) getActivity().findViewById(R.id.imageView3);
        imv4 = (ImageView) getActivity().findViewById(R.id.imageView4);
        imv5 = (ImageView) getActivity().findViewById(R.id.imageView5);
        imv6 = (ImageView) getActivity().findViewById(R.id.imageView6);
        imv7 = (ImageView) getActivity().findViewById(R.id.imageView7);
        imv8 = (ImageView) getActivity().findViewById(R.id.imageView8);
        imv9 = (ImageView) getActivity().findViewById(R.id.imageView9);
    }

    private void setImage() {
        // show progress dialog
        getActivity().runOnUiThread(new Runnable() {
            @Override
            public void run() {
                // set your images here.
            }
        });
        // dismiss progressDialog here
    }
}

Answer 2

如果您想得到一个好的答案，您应该 post 在这里添加一些代码。
一般来说，您可以简单地将可绘制对象用作 ImageView xml 实体中的 "android:src"（您在这里所做的几乎相同，只是使用此处的编程方法...）或者在 Main\UI 线程上使用 Picasso（它与单独负责渲染 UI 组件的线程同名），即在 inflate 方法上。

一般来说，尝试检查更多 'how to' 使用片段和一般 android 设计模式的教程，你显然还在学习，但使用谷歌推荐的方法会更容易您的学习并最大限度地减少错误。

如何在 AsyncTask 中加载 imageView

How to load imageViews in AsyncTask

java

android

android-asynctask

android-fragments

progress-bar