7

我正在使用 aSimpleCursorAdapter和 aListView来显示一些使用 Loader 加载的数据。在里面cursor我有一个int从 0 到 3 的项目。

我希望此 int 等于 0-1 的项目具有布局（右对齐，一种颜色），而具有 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.

有没有简单的方法来做到这一点？类似于开关，其中 0-1 我膨胀 layout_1 和 2-3 我膨胀 layout_2。

编辑：我添加了要填充的 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，我最终的 EventsAdapter（它扩展了 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;
}

    }
4

2 回答 2

10

在使用 ListViews 时，尤其是像您描述的复杂的那样，正确处理视图回收非常重要。该类BaseAdapter是一个超类，SimpleCursorAdapter具有一些方法，您可以覆盖这些方法以在使用最少资源的同时实现您想要的效果。我以前从未使用过 SimpleCursorAdatper，因此在编写时考虑到了普通的 CursorAdapter，但您可以将其与任何覆盖 BaseAdapter 的适配器类一起使用。

Android 中的 ListViews 以一种非常特殊的方式来降低内存成本。当您滚动浏览 ListView 时，移出屏幕的项目的视图被放置在一个小的视图池中。该convertView参数取自该池。他们这样做是因为将每个列表项 View 保留在内存中不能很好地扩展，并且会很快导致 OutOfMemory 异常。该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。通常你会有这样的一行：

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

在这种情况下，如果 convertView 不为空，我们就知道它之前被夸大了。我们不想重新膨胀它，因为这是一个代价高昂的操作，而 getView 应该只是在视图显示之前快速用数据填充视图。

现在，在您的情况下，convertView 有两个潜在的通货膨胀。与其每次都重新膨胀视图（非常糟糕）或对每个视图使用具有唯一资源 id 的某种 hack（更好，但不理想），我们可以覆盖基类中的两个方法以确保 convertView 始终是正确的类型。这两种方法是getItemViewCount()和getItemViewType(int position)。

getItemViewCount()适配器使用它来确定它应该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，适配器使用它来决定应来自哪个池 convertView。在这里，您需要一个 switch 或 if/else 语句来检查底层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 以执行初始 layoutInflation 以便您在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;
}

ListViews 和它们的适配器是我在 Android 中遇到的最复杂的事情之一，但是花时间去做正确的事情会极大地提高你的应用程序的性能和用户体验。祝你好运！

于 2012-08-29T15:55:05.083 回答
0

我认为你只需要在你的getView(int position, View convertView, ViewGroup parent)方法上增加正确的布局：

MyItem item = getItem(position);
View vi = convertView;
if(vi == null){
    switch(item.getStatus())
    {
        case 0:
            vi = mInflater.inflate(R.layout.item1, null);
            break;
        case 1:
            vi = mInflater.inflate(R.layout.item2, null);
            break;
        case 2:
            vi = mInflater.inflate(R.layout.item3, null);
            break;
    }
    //set viewholder ...
}else{
    //get viewholder ...
}
// set values to views ...

这是你需要的吗？

于 2012-08-29T15:12:25.073 回答