Question

我从Udacity视频中多次检查并尝试做同样的事情但listview没有显示。你可以检查一下我的代码并告诉我，如果我错过了什么吗？

MainActivity.java

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.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.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);

           /*//My way
            ArrayList<String> fakeData = new ArrayList<String>();
            fakeData.add("Today-Sunny 50/60");
            fakeData.add("Tomorrow-Cloudy 20/30");
            fakeData.add("Wednesday-Snowy 40/50");
            fakeData.add("Thursday-Rainy 20/40"); */

            //Google's way
            String[] forecastArray={
                    "Today-Sunny 50/60",
                    "Tomorrow-Cloudy 20/30",
                    "Wednesday-Snowy 40/50",
                    "Thursday-Rainy 20/40",
                    "Friday-Funny 20/50",
                    "Sat-Sunny 70/80",
                    "Sun-Sunny 90/100"
            };

            ArrayList<String> weekForecast=new ArrayList<String>();
            Arrays.asList(weekForecast);

            ArrayAdapter adapter = new ArrayAdapter<String>
                    (getActivity(), R.layout.list_item_forecast, R.id.list_item_forecast_textview, weekForecast);

            ListView listview = (ListView) rootView.findViewById(R.id.listview_forecast);

            listview.setAdapter(adapter);

            return rootView;
        }


    }
}

activity_main.xml中

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    tools:ignore="MergeRootFrame"/>

fragment_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$PlaceholderFragment">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/listview_forecast" />
</FrameLayout>

list_item_forecast.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:minHeight="?android:attr/listPreferredItemHeight"
    android:gravity="center_vertical"
    android:id="@+id/list_item_forecast_textview">
</TextView>

Answer 1

问题是weekForecast已声明但未初始化。替换：

ArrayList<String> weekForecast=new ArrayList<String>();
Arrays.asList(weekForecast);

使用：

ArrayList<String> weekForecast = new ArrayList<String>(Arrays.asList(forecastArray));

Udacity- Android First Lesson，Listview没有出现

1 个答案: