從Parse.com填充列表

Question

我想從parse.com獲得一列字符串，並使用ArrayAdapter將它們加載到ListView。 它似乎在日誌中我試圖加載的字符串數組是空的（然後寫入「storage = null」）。 我不明白是什麼問題。 我正在從MainActivity中解析字符串，然後用我之前創建的字符串數組初始化適配器。 在此先感謝。

MainActivity

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); 
} 
} 

適配器

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; 

     }; 
    } 

日誌（錯誤）

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

你得到的是錯誤的，因爲當它傳遞給適配器字符串數組爲null。

我將String從String []更改爲ArrayList，並在onCreate中將其瞬發，並將新歌曲添加到列表後調用adapter.notifyDataSetChanged（）以讓適配器知道新項目已添加到列表並刷新它。

下面是更新後的類：

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); 
    } 
}