将可见性设置为 VISIBLE 时不显示进度条

Question

我正在创建一个程序，它应该在后台执行某些操作时显示进度条（使用AsyncTask），当任务完成时，进度条会消失并显示结果。

我在RecyclerView 中添加了一个进度条，但将其可见性设置为消失。 在 AsyncTask PreExecute 中，我将其可见性设置为 VISIBLE，在 OnPostExecute 中，我将其可见性设置为 GONE，但是当我运行应用程序时，进度条根本不显示。

我已经包含了 XML：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context=".MainActivity"
tools:showIn="@layout/activity_main">

<android.support.v4.widget.ContentLoadingProgressBar
    android:id="@+id/rv_progress_bar"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:indeterminate="true"
    android:indeterminateTint="@color/plus_icon_color"
    android:visibility="gone" />

<android.support.v7.widget.RecyclerView
    android:id="@+id/train_rv"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:scrollbars="vertical" />

和 Java 代码：

public class MainActivity extends AppCompatActivity {
private RecyclerView mTrainsRv;
private TrainAdapter mTrainAdapter;
ArrayList<Train> trains = new ArrayList<>();
ProgressBar mRvProgress;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    mRvProgress = (ProgressBar)findViewById(R.id.rv_progress_bar);
    mTrainsRv = (RecyclerView) findViewById(R.id.train_rv);
    mTrainsRv.setLayoutManager(new LinearLayoutManager(this));
    mTrainAdapter = new TrainAdapter(createDefaultTrains());
    mTrainsRv.setAdapter(mTrainAdapter);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            trains.add(new Train(4, "Berowra Platform 4", 12, "Late", "Beverly", "15:18"));
            mTrainAdapter.notifyDataSetChanged();
        }
    });
}

private List<Train> createDefaultTrains() {
    trains.add(new Train(0, "Albion Park Platform 1", 3, "On Time", "Allawah", "14:11"));
    trains.add(new Train(1, "Arncliffe Platform 2", 4, "Late", "Central", "14:34"));
    trains.add(new Train(2, "Artarmion Platform 3", 7, "On Time", "Ashfield", "15:01"));
    trains.add(new Train(3, "Berowra Platform 4", 12, "Late", "Beverly", "15:18"));
    return trains;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    // Handle item selection
    switch (item.getItemId()) {
        case R.id.action_delete:
            trains.clear();
            mTrainAdapter.notifyDataSetChanged();
            return true;
        case R.id.action_refresh:
            new RefreshProgressAsync().execute();
            return true;
        case R.id.action_quit:
            Toast.makeText(this, R.string.quit_menu,
                    Toast.LENGTH_LONG).show();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}
private class RefreshProgressAsync extends AsyncTask<Void,Void,Integer> {
private int mGenerated;

    @Override
    protected Integer doInBackground(Void... voids) {
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        int ran = 0;
        Random r = new Random();
        for(int i=0; i<trains.size(); i++) {
            int min = 1;
            int max = 20;
            ran = r.nextInt(max - min + 1) + min;
            mGenerated = ran;
        }
        return mGenerated;
    }

    @Override
    protected void onPreExecute() {
        mRvProgress.setVisibility(View.VISIBLE);
        mTrainsRv.setAlpha(0);
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Integer arrivalTime) {
        super.onPostExecute(arrivalTime);
        for (int i=0; i<trains.size();i++){
            trains.get(i).setArrivalTime(arrivalTime);
        }
        mTrainAdapter.notifyDataSetChanged();
        mTrainsRv.setAlpha(1);
        mRvProgress.setVisibility(View.GONE);
    }
}

我不知道为什么它没有显示。 谢谢

Answer 1

它的行为符合预期。 ContentLoadingProgressBar 的目的是仅在必要时显示进度。如果操作花费的时间很短，则不会显示进度条。这是为了避免出现进度条闪烁效果，快速连续显示和消失。

如果您想让它可见以用于测试目的（我不建议在生产代码中使用），请将您的睡眠时间增加到 10 秒：

 @Override
  protected Integer doInBackground(Void... voids) {
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        ....
  } 

或者你也可以使用普通的ProgressBar