基于 ListItem 特定变量对 ListItem 进行膨胀布局

我正在使用一个SimpleCursorAdapter and a ListView显示使用 Loader 加载的一些数据。 在 - 的里面cursor我的物品带有int从 0 到 3。

我希望此 int 等于 0-1 的项目具有布局（右对齐，一种颜色），而 2-3 的项目具有另一种布局（左对齐，另一种颜色）。much like a chat app, where sent messages are on the right and received ones are on the left.

有简单的方法吗？就像一个开关，其中 0-1 我膨胀布局 _1 和 2-3 我膨胀布局 _2。

编辑：我已经添加了我要填充的 ListFragment 的代码。用作开关的 int 是 MyContentProvider.Data.E_TYPE。 我无法掌握它，但也许有人可以清楚地解释我必须写什么！

   import com.actionbarsherlock.view.Menu;
   import com.actionbarsherlock.view.MenuInflater;
   import com.corsalini.survcontr.MyContentProvider.Data;

   import android.content.ContentResolver;
   import android.content.ContentValues;
   import android.database.Cursor;
   import android.os.Bundle;
   import android.support.v4.app.ListFragment;
   import android.support.v4.content.CursorLoader;
   import android.support.v4.app.LoaderManager;
   import android.support.v4.content.Loader;
   import android.support.v4.widget.CursorAdapter;
   import android.support.v4.widget.SimpleCursorAdapter;
   import android.util.Log;
   import android.view.View;
   import android.widget.ListView;



  public class FragEvents extends ListFragment implements  LoaderManager.LoaderCallbacks<Cursor>{
@Override
public void onPause() {
    allRead();
    super.onPause();

}

private static final int EVENTS_LOADER = 0x02;

// This is the Adapter being used to display the list's data.
SimpleCursorAdapter mAdapter;

// If non-null, this is the current filter the user has provided.
String mCurFilter;

@Override public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    // Give some text to display if there is no data.  In a real
    // application this would come from a resource.
    setEmptyText(this.getString(R.string.perform_event)); 

    // We have a menu item to show in action bar.
    setHasOptionsMenu(true);

    // Create an empty adapter we will use to display the loaded data.
    mAdapter = new SimpleCursorAdapter(getActivity(),
            android.R.layout.simple_list_item_2, null,
            new String[] { MyContentProvider.Data.E_TEXT, MyContentProvider.Data.E_DATE, 
        MyContentProvider.Data.E_NUMBER, MyContentProvider.Data.E_TYPE  },
        new int[] { android.R.id.text1, android.R.id.text2 },
        CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
    setListAdapter(mAdapter);

    // Start out with a progress indicator.
    setListShown(false);

    // Prepare the loader.  Either re-connect with an existing one,
    // or start a new one.
    getActivity().getSupportLoaderManager().initLoader(EVENTS_LOADER, null, this);


}

public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
     inflater.inflate(R.menu.menu_events, menu);  
}



@Override public void onListItemClick(ListView l, View v, int position, long id) {
    //TODO Insert desired behavior here.
    Log.i("FragmentComplexList", "Item clicked: " + id);
}

// These are the Contacts rows that we will retrieve.
static final String[] SUMMARY_PROJECTION = new String[] {
    MyContentProvider.Data.E_ID,
    MyContentProvider.Data.E_DATE,
    MyContentProvider.Data.E_NUMBER,
    MyContentProvider.Data.E_TEXT,
    MyContentProvider.Data.E_TYPE,

};

public Loader<Cursor> onCreateLoader(int id, Bundle args) {


    return new CursorLoader(getActivity(),  MyContentProvider.Data.CONTENT_URI_EVENTS,
            SUMMARY_PROJECTION, null, null,
            Data.E_ID + " DESC");
}

public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    // Swap the new cursor in.  (The framework will take care of closing the
    // old cursor once we return.)
    mAdapter.swapCursor(data);

    // The list should now be shown.
    if (isResumed()) {
        setListShown(true);
    } else {
        setListShownNoAnimation(true);
    }
}

public void onLoaderReset(Loader<Cursor> loader) {
    // This is called when the last Cursor provided to onLoadFinished()
    // above is about to be closed.  We need to make sure we are no
    // longer using it.
    mAdapter.swapCursor(null);
}

public void deleteEvent(ContentResolver contentResolver,
        long id){
    String selection = Data.E_ID + "=";
    String[] args = {String.valueOf(id)};
    contentResolver.delete(Data.CONTENT_URI_EVENTS, selection, args);
}

public void allRead(){
    ContentResolver contentResolver = getActivity().getContentResolver();
    ContentValues contentValue = new ContentValues();
    contentValue.put(Data.E_NUMBER, Data.RECEIVED_READ);
    String selection= Data.E_TYPE+"=";
    String[] args= {String.valueOf(Data.RECEIVED_UNREAD)};
    contentResolver.update(Data.CONTENT_URI_EVENTS, contentValue, selection, args);
}



   }

编辑：如果我做对了，我的最终 EventsAdapter （扩展了 SimpleCursorAdapter）应该如下所示：

    import android.content.Context;
    import android.database.Cursor;
    import android.support.v4.widget.SimpleCursorAdapter;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.TextView;

    public class EventsAdapter extends SimpleCursorAdapter {

private Context localContext;

public EventsAdapter(Context context, int layout, Cursor c, String[] from,
        int[] to, int flags) {
    super(context, layout, c, from, to, flags);

    localContext = context;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    Cursor c= getCursor();
    c.moveToPosition(position);
    if(convertView == null)
    {
        LayoutInflater layoutInflator = (LayoutInflater)localContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        switch (getItemViewType(position)){
        case 0:
            convertView = layoutInflator.inflate(R.layout.item_event_0, null);
            break;
        case 1:
            convertView = layoutInflator.inflate(R.layout.item_event_1, null);
            break;
        case 2:
            convertView = layoutInflator.inflate(R.layout.item_event_2, null);
            break;
        case 3:
            convertView = layoutInflator.inflate(R.layout.item_event_3, null);
            break;
        }

    }
    switch (getItemViewType(position)){
    case 0:
        TextView date0=(TextView)convertView.findViewById(R.id.date0);
        TextView text0=(TextView)convertView.findViewById(R.id.text0);
        date0.setText(""+c.getString(c.getColumnIndex(Data.E_DATE)));
        text0.setText(""+c.getString(c.getColumnIndex(Data.E_TEXT)));
        break;
    case 1:
        TextView date1=(TextView)convertView.findViewById(R.id.date1);
        TextView text1=(TextView)convertView.findViewById(R.id.text1);
        date1.setText(""+c.getString(c.getColumnIndex(Data.E_DATE)));
        text1.setText(""+c.getString(c.getColumnIndex(Data.E_TEXT)));
    case 2:
        TextView date2=(TextView)convertView.findViewById(R.id.date2);
        TextView text2=(TextView)convertView.findViewById(R.id.text2);
        date2.setText(""+c.getString(c.getColumnIndex(Data.E_DATE)));
        text2.setText(""+c.getString(c.getColumnIndex(Data.E_TEXT)));
    case 3:
        TextView date3=(TextView)convertView.findViewById(R.id.date3);
        TextView text3=(TextView)convertView.findViewById(R.id.text3);
        date3.setText(""+c.getString(c.getColumnIndex(Data.E_DATE)));
        text3.setText(""+c.getString(c.getColumnIndex(Data.E_TEXT)));
    }
    return convertView;
}

@Override
public int getItemViewType(int position) {
    int type = 0;
    int returnInt = 0;
    Cursor c= getCursor();
    c.moveToPosition(position);
    type= c.getInt(c.getColumnIndex(Data.E_TYPE));
    switch (type){
    case Data.RECEIVED_READ:
        returnInt=3;
    case Data.RECEIVED_UNREAD: 
        returnInt= 2;
    case Data.SENT_COMPLETED:
        returnInt= 1;
    case Data.SENT_PROGRESS:
        returnInt= 0;
    default:
        returnInt=0;
    }
    return returnInt;
}

@Override
public int getViewTypeCount() {
    return 4;
}

    }

使用 ListView 时，尤其是像您描述的复杂的 ListView 时，正确处理视图回收非常重要。这BaseAdapter类，超类SimpleCursorAdapter有一些方法可以覆盖，以使用最少的资源实现您想要的效果。我以前从未使用过 SimpleCursorAdatper，因此这是使用普通 CursorAdapter 编写的，但您可以将其与覆盖 BaseAdapter 的任何 Adapter 类一起使用。

Android 中的 ListView 以非常特定的方式运行以降低内存成本。当您滚动 ListView 时，移出屏幕的项目的视图将放置在一个小的视图池中。这convertView参数是从该池中获取的。他们这样做是因为将每个列表项视图保留在内存中不能很好地扩展，并且可能很快导致 OutOfMemory 异常。这getView()方法是您获取这些视图并为当前列表项配置它们的地方。通常你会看到这样的一行：

if(convertView == null)
    convertView = layoutInflator.inflate(R.layout.list_item, null);

在这种情况下，如果convertView不为null，我们就知道它之前已经被膨胀了。我们不想重新填充它，因为这是一个代价高昂的操作，并且 getView 应该在显示视图之前快速用数据填充视图。

现在，就您的情况而言，convertView 有两种潜在的通货膨胀。我们可以重写基类中的两个方法来确保 ConvertView 始终是正确的，而不是每次都重新填充视图（非常糟糕）或使用某种为每个视图提供唯一资源 ID 的 hack（更好，但不理想）类型。这两种方法是getItemViewCount() and getItemViewType(int position).

getItemViewCount()适配器使用它来确定应为列表维护多少个视图池。覆盖它很简单，在你的情况下看起来像这样。

@Override
public int getViewTypeCount()
{
    return 2; //Even though you have four cases, there are only 2 view types.
}

getItemViewType(int position)在调用 getView 之前由适配器使用来决定 ConvertView 应该来自哪个池。在这里，您需要一个 switch 或 if/else 语句来检查基础数据源的视图类型并返回它。 （请注意，根据 Android 文档，此处的返回值必须介于 0 和 getViewTypeCount() -1 之间，因此在您的情况下为 0 或 1。）

@Override
public int getItemViewType(int position)
{
    Item item = getItem(position)  //Or however you're getting the data associated with a particular list position
    switch(item.myInt)
    {
         //I simplified this a bit, basically, check your int, if it's the first type, return 0 for your first layout type, else return 1 for your second.
         case(0):
         case(1):
             return 0;
         case(2):
         case(3):
             return 1;
    }
}

现在，最后，我们将修改 getView 来执行初始layoutInflation，以便您的池中拥有正确的视图。

@Override
public View getView(int position, View convertView, ViewGroup viewParent)
{
    //if convertView is not null, we got a view from the pool, just go on
    if(convertView == null)
    {
        //This means we didn't have a view in the pool to match this view type.  Inflate it and it will be placed in the proper pool when this list item is scrolled off the screen
        if(getItemViewType(position) == 0)
            convertView = layoutInflator.inflate(R.layout.list_item_type1, null);
        else if(getItemViewType(position) == 1)
            convertView = layoutInflator.inflate(R.layout.list_item_type2, null);
    }

    //Populate the view with whatever data you need here

    //And finally....
    return convertView;
}

ListView 及其适配器是我在 Android 中遇到的最复杂的事情之一，但是花时间正确地完成它将会极大地提高应用程序的性能和用户体验。祝你好运！