Question

所以我试图使用Picasso Library进行图像下载和缓存。为了让contactUri传递给Picasso，我需要查询联系人Content Provider。由于我不想阻止主UI线程获取contactId，因此我将其放在AsyncTask中。一旦我获得了contactId，我就会在Picasso的{{1}}方法中拨打onPostExecute()。

然而，我注意到当我快速滚动AsyncTask时出现的闪烁现象。在我看来，ListView存在问题，因为在设置适当的图像之前，回收的视图正在显示上一个图像。反正有没有避免这个？

ViewHolder

Answer 1

只需在getView中将imageview设置为null，它就应该删除你正在经历的大部分内容。

另一个微小的小角落情况是，当你的asynctask到达postExecute时，视图可能仍然存在，但它可能已被分配了一个不同的联系人来加载（它已被回收）。

您需要在视图中放置某种标记，然后在postexecute中设置它时检查它是否仍然相同。

要删除淡入，您需要从getview中删除asynctask。您需要能够在getview中调用picasso，这意味着在到达getview之前准备好数据。

下面，不太确定它是否会编译，我已经在文本编辑器中完成了。

但是低音我正在缓存mCachedContactIds中的结果，如果我需要一个新表，只需重新加载整个表。我通常发现这很强大。但你也可以调用我已经注释掉的毕加索代码

public class ConversationThreadsCursorAdapter extends SimpleCursorAdapter {

// region Constants
private static final int RECIPIENT_IDS_COLUMN_INDEX = 3;
private static final int ID2_COLUMN_INDEX = 0;
private static final int ADDRESS_COLUMN_INDEX = 1;
private HashMap<String, Integer> mCachedContactIds = new HashMap<String, Integer>();
// endregion

// region Variables
private final String DEBUG_TAG = getClass().getSimpleName().toString(); 
private Context mContext;
protected Drawable mDefaultPicDrawable;
protected ContentResolver mContentResolver;
protected LinearLayout.LayoutParams mContactPicLayoutParams;
// endregion

// region Constructors
public ConversationThreadsCursorAdapter(Context context, int layout,
Cursor c, String[] from, int[] to, int flags) {
    super(context, layout, c, from, to, flags);
    mContext = context;
    mDefaultPicDrawable = mContext.getResources().getDrawable(
    R.drawable.ic_contact_picture);
    mContactPicLayoutParams = new LinearLayout.LayoutParams(
    mDefaultPicDrawable.getIntrinsicWidth(),
    mDefaultPicDrawable.getIntrinsicHeight());

}
// endregion

public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder viewHolder = null;

    if (convertView == null) {
        convertView = mLayoutInflater.inflate(R.layout.simple_message, null);    
        // Creates a ViewHolder and store references to the children
        // views we want to bind data to.
        viewHolder = setupViewHolder(convertView);  
        convertView.setTag(viewHolder);

    } else {
        // Get the ViewHolder back to get fast access to the TextView
        // and the ImageView.
        viewHolder = (ViewHolder) convertView.getTag();
        viewHolder.task.cancel(true);
        viewHolder.contactBadge.setImageDrawable(mDefaultPicDrawable);
    }

    mCursor = getCursor();

    mCursor.moveToPosition(position);

    viewHolder.position = position;

    String recipient_ids = mCursor.getString(RECIPIENT_IDS_COLUMN_INDEX);

    String[] recipients = recipient_ids.split(" ");
    String recipient = recipients[0];

    if(mCachedContactIds.get(recipient) != null){
        Picasso.with(mContext)
            .load(getContactUri(mCachedContactIds.get(recipient)))
            .placeholder(R.drawable.ic_contact_picture)
            .into(mViewHolder.contactBadge);                 
    } else {
        viewHolder.task = new AddressFetcherTask(viewHolder, position);
        viewHolder.task.execute(recipients); 
    }

    return convertView;    
}

// region Helper Methods
private ViewHolder bindUIElements(View convertView) {
    ViewHolder viewHolder = new ViewHolder();    
    viewHolder.contactBadge = (QuickContactBadge) convertView.findViewById(R.id.contact_pic);
    return viewHolder;
}

private ViewHolder setupViewHolder(View convertView) {
    ViewHolder viewHolder = bindUIElements(convertView);    
    viewHolder.contactBadge.setLayoutParams(mContactPicLayoutParams);
    return viewHolder;
}
// endregion

// region Inner Classes

private class ViewHolder {
    QuickContactBadge contactBadge;
    int position;
    AddressFetcherTask task;
}

private class AddressFetcherTask extends AsyncTask < String[], Void, Integer > {
    private ViewHolder mViewHolder;
    private int mPosition;
    private String mRecipient;

    public AddressFetcherTask(ViewHolder viewHolder, int position) {
        mViewHolder = viewHolder;
        mPosition = position;
    }

    @Override
    protected Integer doInBackground(String[]...recipients) {
        mRecipient = recipients[0][0];
        Log.d(DEBUG_TAG, "recipient is " + recipient);
        Cursor c = mContentResolver.query(
        Uri.parse("content://mms-sms/canonical-addresses"), null, "_id = " + mRecipient, null, null);

        String _id = "";
        String address = "";
        while (c.moveToNext()) {
            _id = c.getString(ID2_COLUMN_INDEX);
            address = c.getString(ADDRESS_COLUMN_INDEX);
        }
        c.close();

        int contactId;
        if (address != null) {
            contactId = ContactsUtils.getContactId(mContext, address, "address");
        } else {
            contactId = Integer.valueOf(address);
        }
        return contactId;
    }

    @Override
    protected void onPostExecute(Integer contactId) {                           
        if (mViewHolder.position == mPosition) {
            mCachedContactIds.put(mRecipient, contactId);

            Picasso.with(mContext)
                .load(getContactUri(mCachedContactIds.get(recipient)))
                .placeholder(R.drawable.ic_contact_picture)
                .into(mViewHolder.contactBadge);
        }               
    }
}  
// endregion

}

或者，如果所有这些让你感到困扰的是毕加索的淡出，那么在请求中添加noFade（）。

毕加索加载的图像在AsyncTask中产生

1 个答案: