Question

有人可以帮我理解progressBar.setVisibility()在使用CountDownTimer时的效果，但在async下载时却不行吗？实际上，Toast下载async上的onPostExecute()即使第二个public class MainActivity extends AppCompatActivity { ProgressBar progressBar; int[] items = { 12982418, 12998698, 12993549, 12995125, 12987537, 12993021, 12991986, 13008408, 12983417, 12986060, 12998395, 12985644, 13014731, 12986433, 12985074, 12994455, 12994262, 12986759, 13011932, 13005211, 12993521, 12987900, 12992623, 12981736, 12986649, 12991524, 13000035, 12989278, 13013868, 13009417, 13013327, 12981605, 12985768, 13000158, 13015035, 13002596, 13015944, 12997893, 12999767, 13010949, 12996835, 13013517, 13006555, 13013143, 13010016, 13005792, 13016948, 13007235, 12998343, 12987102 }; int counter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); progressBar = (ProgressBar) findViewById(R.id.progressBar); progressBar.setIndeterminate(true); progressBar.setKeepScreenOn(true); progressBar.setVisibility(View.INVISIBLE); } public void actionTimer(View view) { Toast.makeText(this, "starting progressBar - CountDownTimer", Toast.LENGTH_SHORT).show(); progressBar.setVisibility(View.VISIBLE); new CountDownTimer(5000, 500) { @Override public void onTick(long millisUntilFinished) { } @Override public void onFinish() { progressBar.setVisibility(View.INVISIBLE); Toast.makeText(getApplicationContext(), "timer done", Toast.LENGTH_SHORT).show(); } }.start(); } public void actionJson(View view) { Toast.makeText(this, "starting progressBar - json fetch", Toast.LENGTH_SHORT).show(); progressBar.setVisibility(View.VISIBLE); String urlTemplate = "https://hacker-news.firebaseio.com/v0/item/___ITEM_NUMBER___.json?print=pretty"; counter = 0; for (int i = 0; i < items.length; i++) { String url = urlTemplate.replaceAll("___ITEM_NUMBER___", String.valueOf(items[i])); //Log.i("thisDoesNotWork", url); DownloadJson downloadJson = new DownloadJson(); try { downloadJson.execute(url).get(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } } public class DownloadJson extends AsyncTask<String, Void, String> { @Override protected String doInBackground(String... params) { Log.i("DownloadJson", "url=" + params[0]); URL url; HttpURLConnection urlConnection = null; try { url = new URL(params[0]); urlConnection = (HttpURLConnection) url.openConnection(); InputStream inputStream = urlConnection.getInputStream(); BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream)); StringBuilder resultBuilder = new StringBuilder(); String line; while ((line = reader.readLine()) != null) { resultBuilder.append(line).append("\n"); } //Log.i("DownloadJson", "resultBuilder.length()=" + resultBuilder.length()); return resultBuilder.toString(); } catch (Exception e) { e.printStackTrace(); return "{\"status\" : \"Hacker News json download failed\"}"; } } @Override public void onPostExecute(String s) { super.onPostExecute(s); counter += 1; if (counter == items.length) { progressBar.setVisibility(View.INVISIBLE); Toast.makeText(getApplicationContext(), "download done", Toast.LENGTH_SHORT).show(); } } } }也没有显示。下面是一个工作，或者说不工作的演示。非常感谢。

我的 MainActivity ：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.plaudev.progressbar.MainActivity">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_vertical">

        <Button
            android:text="@string/timer"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:id="@+id/buttonTimer"
            android:layout_weight="1"
            android:onClick="actionTimer"
            android:layout_margin="25dp" />

        <Button
            android:text="@string/json"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/buttonJson"
            android:layout_weight="1"
            android:onClick="actionJson"
            android:layout_margin="25dp" />
    </LinearLayout>

    <ProgressBar
        style="?android:attr/progressBarStyleLarge"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/progressBar" />
</RelativeLayout>

我的 XML ：

RecurringJob.AddOrUpdate("Process inbound external messages", () => ProcessInboundExternalMessages(), Cron.Minutely);

Answer 1

答案是将onClick for中的整个actionJson()循环放入工作线程中，如下所示noted here：

public void actionJson(View view) {
        Toast.makeText(this, "starting progressBar - json fetch", Toast.LENGTH_SHORT).show();
        progressBar.setVisibility(View.VISIBLE);

        final String urlTemplate = "https://hacker-news.firebaseio.com/v0/item/___ITEM_NUMBER___.json?print=pretty";
        counter = 0;

        // simply put it in a worker thread does the job
        new Thread(new Runnable() {
            public void run() {
                for (int i = 0; i < items.length; i++) {
                    String url = urlTemplate.replaceAll("___ITEM_NUMBER___", String.valueOf(items[i]));
                    //Log.i("actionJson", url);
                    DownloadJson downloadJson = new DownloadJson();
                    try {
                        downloadJson.execute(url).get();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } catch (ExecutionException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }

因此，即使最初定义的for循环确实单独生成了一大堆asyncTasks，它仍然以某种方式阻塞主线程。

Android progressBar setVisibility（）不起作用

1 个答案: