android - 从 Parse.com 填充列表

Question

我正在尝试从 parse.com 获取一列字符串并使用 ArrayAdapter 将它们加载到 ListView。在日志中，我尝试加载的字符串数组似乎是空的(然后写为“storage=null”)。我不明白是什么问题。我在 MainActivity 中从解析加载字符串，然后使用我之前创建的字符串数组初始化适配器。提前致谢。

主要 Activity

public class MainActivity extends AppCompatActivity {
ListView list;
String[] itemname ;
String[] Strings;
Integer[] imgid={
        R.drawable.one,
        R.drawable.one,
        R.drawable.one,
        R.drawable.one,
        R.drawable.one,
        R.drawable.one,
        R.drawable.one,
        R.drawable.one,
};
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);


    ParseQuery<ParseObject> query = ParseQuery.getQuery("Song");
    query.orderByDescending("updatedAt");
    query.findInBackground(new FindCallback<ParseObject>() {
        public void done(List<ParseObject> songs, ParseException e) {
            if (e == null) {
                 Strings = new String[songs.size()-1];
                for (int i = 0; i < songs.size()-1; i++) {
                    ParseObject object = songs.get(i);
                    String songName = object.getString("name");
                    Strings[i] = songName;
                }
            } else {
                Log.d("error", "Error: " + e.getMessage());
            }
        }
    });

    CustomListAdapter adapter=new CustomListAdapter(this, Strings);

    list=(ListView)findViewById(R.id.list);
    list.setAdapter(adapter);

    list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
            // TODO Auto-generated method stub
            String Slecteditem= itemname[+position];
            Toast.makeText(getApplicationContext(), Slecteditem, Toast.LENGTH_SHORT).show();

        }
    });

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    return super.onOptionsItemSelected(item);
}
}

适配器

public class CustomListAdapter extends ArrayAdapter<String> {

    private final Activity context;
    private final String[] itemname;

    public CustomListAdapter(Activity context, String[] itemname) {
        super(context, R.layout.content_main, itemname);

        this.context=context;
        this.itemname=itemname;
    }


public  TextView extratxt;
    public View getView(int position,View view,ViewGroup parent) {
        LayoutInflater inflater=context.getLayoutInflater();
        View rowView=inflater.inflate(R.layout.line_single, null,true);

        TextView txtTitle = (TextView) rowView.findViewById(R.id.Poet);
        TextView dayView = (TextView) rowView.findViewById(R.id.Day);
         extratxt = (TextView) rowView.findViewById(R.id.SongaName);

        txtTitle.setText("hello");
        dayView.setText("D");

        extratxt.setText("Description " + itemname[position]);

        return rowView;

        };
    }

日志(错误)

   java.lang.RuntimeException: Unable to start activity ComponentInfo{.MainActivity}: java.lang.NullPointerException: storage == null
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2378)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2440)
                                                                             at android.app.ActivityThread.access$800(ActivityThread.java:162)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                             at android.os.Looper.loop(Looper.java:135)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5430)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at java.lang.reflect.Method.invoke(Method.java:372)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:913)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:706)
                                                                          Caused by: java.lang.NullPointerException: storage == null
                                                                             at java.util.Arrays$ArrayList.<init>(Arrays.java:38)
                                                                             at java.util.Arrays.asList(Arrays.java:155)
                                                                             at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:128)
                                                                             at shirapp.israel.nir_zabari.shira.CustomListAdapter.<init>(CustomListAdapter.java:16)
                                                                             at shirapp.israel.nir_zabari.shira.MainActivity.onCreate(MainActivity.java:62)
                                                                             at android.app.Activity.performCreate(Activity.java:6097)
                                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2331)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2440) 
                                                                             at android.app.ActivityThread.access$800(ActivityThread.java:162) 
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) 
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                             at android.os.Looper.loop(Looper.java:135) 
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5430) 
                                                                             at java.lang.reflect.Method.invoke(Native Method) 
                                                                             at java.lang.reflect.Method.invoke(Method.java:372) 
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:913) 
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:706) 

Answer 1

您收到该错误是因为字符串数组在传递给适配器时为空。

我将字符串从 String[] 更改为 ArrayList 并在 onCreate 中实例化它，在将新歌曲添加到列表后调用 adapter.notifyDataSetChanged() 让适配器知道新项目已添加到列表并刷新它.

这是更新后的类:

public class MainActivity extends AppCompatActivity {
    ListView list;
    CustomListAdapter adapter;
    String[] itemname ;
    ArrayList<String> Strings;
    Integer[] imgid={
            R.drawable.one,
            R.drawable.one,
            R.drawable.one,
            R.drawable.one,
            R.drawable.one,
            R.drawable.one,
            R.drawable.one,
            R.drawable.one,
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        Strings = new ArrayList();

        ParseQuery<ParseObject> query = ParseQuery.getQuery("Song");
        query.orderByDescending("updatedAt");
        query.findInBackground(new FindCallback<ParseObject>() {
            public void done(List<ParseObject> songs, ParseException e) {
                if (e == null) {
                    for (int i = 0; i < songs.size() - 1; i++) {
                        ParseObject object = songs.get(i);
                        String songName = object.getString("name");
                        Strings.add(songName);
                        adapter.notifyDataSetChanged();
                    }
                } else {
                    Log.d("error", "Error: " + e.getMessage());
                }
            }
        });

        adapter = new CustomListAdapter(this, Strings);

        list=(ListView)findViewById(R.id.list);
        list.setAdapter(adapter);

        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                // TODO Auto-generated method stub
                String Slecteditem= itemname[+position];
                Toast.makeText(getApplicationContext(), Slecteditem, Toast.LENGTH_SHORT).show();

            }
        });

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        return super.onOptionsItemSelected(item);
    }
}