Question

我对Android很新，我有一个问题，我不知道从哪里开始寻找它的原因。

我有一个片段，其中ListView填充了Loader。当我启动应用时，ListView会显示两次，一个显示在另一个上面，下面是截图：

我不知道从哪里开始寻找发生这种情况的原因，但我想我必须提供一些代码，所以这里是我的片段代码：

public class ForecastFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor> {

    private static final int FORECAST_LOADER = 0;
    // For the forecast view we're showing only a small subset of the stored data.
    // Specify the columns we need.
    private static final String[] FORECAST_COLUMNS = {
            // In this case the id needs to be fully qualified with a table name, since
            // the content provider joins the location & weather tables in the background
            // (both have an _id column)
            // On the one hand, that's annoying.  On the other, you can search the weather table
            // using the location set by the user, which is only in the Location table.
            // So the convenience is worth it.
            WeatherContract.WeatherEntry.TABLE_NAME + "." + WeatherContract.WeatherEntry._ID,
            WeatherContract.WeatherEntry.COLUMN_DATE,
            WeatherContract.WeatherEntry.COLUMN_SHORT_DESC,
            WeatherContract.WeatherEntry.COLUMN_MAX_TEMP,
            WeatherContract.WeatherEntry.COLUMN_MIN_TEMP,
            WeatherContract.LocationEntry.COLUMN_LOCATION_SETTING,
            WeatherContract.WeatherEntry.COLUMN_WEATHER_ID,
            WeatherContract.LocationEntry.COLUMN_COORD_LAT,
            WeatherContract.LocationEntry.COLUMN_COORD_LONG
    };

    // These indices are tied to FORECAST_COLUMNS.  If FORECAST_COLUMNS changes, these
    // must change.
    static final int COL_WEATHER_ID = 0;
    static final int COL_WEATHER_DATE = 1;
    static final int COL_WEATHER_DESC = 2;
    static final int COL_WEATHER_MAX_TEMP = 3;
    static final int COL_WEATHER_MIN_TEMP = 4;
    static final int COL_LOCATION_SETTING = 5;
    static final int COL_WEATHER_CONDITION_ID = 6;
    static final int COL_COORD_LAT = 7;
    static final int COL_COORD_LONG = 8;

    private ForecastAdapter mForecastAdapter;

    public ForecastFragment() {
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);
        inflater.inflate(R.menu.menu_main, menu);
    }

    @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.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            startActivity(new Intent(getActivity(), SettingsActivity.class));
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // The CursorAdapter will take data from our cursor and populate the ListView.
        mForecastAdapter = new ForecastAdapter(getActivity(), null, 0);

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

        ListView listView = (ListView)rootView.findViewById(R.id.listview_forecast);
        listView.setAdapter(mForecastAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                // CursorAdapter returns a cursor at the correct position for getItem(), or null
                // if it cannot seek to that position
                Cursor cursor = (Cursor) adapterView.getItemAtPosition(position);
                if (cursor != null) {
                    String locationSetting = Utility.getPreferredLocation(getActivity());
                    Intent detailIntent = new Intent(getActivity(), DetailActivity.class)
                            .setData(WeatherContract.WeatherEntry.buildWeatherLocationWithDate(
                                    locationSetting, cursor.getLong(COL_WEATHER_DATE)
                            ));
                    startActivity(detailIntent);
                }
            }
        });
        return rootView;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        getLoaderManager().initLoader(FORECAST_LOADER, null, this);
        super.onActivityCreated(savedInstanceState);
    }

    private void updateWeather(){
        FetchWeatherTask weatherTask = new FetchWeatherTask(getActivity());
        String location = Utility.getPreferredLocation(getActivity());
        weatherTask.execute(location);
    }

    void onLocationChanged() {
        updateWeather();
        getLoaderManager().restartLoader(FORECAST_LOADER, null, this);
    }

    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        String location = Utility.getPreferredLocation(getActivity());

        //Sort order: Ascending by date
        String sortOrder = WeatherContract.WeatherEntry.COLUMN_DATE + " ASC";
        Uri weatherForLocation = WeatherContract.WeatherEntry.buildWeatherLocationWithStartDate(
                location, System.currentTimeMillis());

        return new CursorLoader(getActivity(),
                weatherForLocation,
                FORECAST_COLUMNS,
                null,
                null,
                sortOrder);
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        if (!data.moveToFirst())
            updateWeather();
        mForecastAdapter.swapCursor(data);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        mForecastAdapter.swapCursor(null);
    }
}

Answer 1

从我在屏幕截图中看到的内容看起来，您将两次相同的片段添加到当前视图的层次结构中。最常见的错误是使用Activity标签在<fragment的布局中声明片段，并使用特定的事务以编程方式声明，这当然会导致在屏幕上两次使用相同的片段。要解决此问题，请使用<fragment替换布局中的<FrameLayout，然后以编程方式添加片段。 E.g。

<FrameLayout 
  android:id="@+id/container"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content" />

并在您的Activity的onCreate

中

if (savedInstanceState == null){ 
    getSupportFragmentManager() .beginTransaction() .add(R.id.container, new ForecastFragment(), FORECASTFRAGMENT_TAG) .commit(); 
}

Answer 2

发生的事情是你通过XML声明片段，然后再次膨胀。

你应该使用更好的方法而不是将片段放在XML中，添加一个空的framelayout并每次添加/替换片段（看看我在自定义库中的this方法），这样它只会显示一次，或者不再对它进行充气（但是onResume也可以复制它，并且没有提供更改正在显示的片段的自由）。

Android ListView被充气两次

2 个答案: