ListView getView-如果在第一次滚动时未调用if(convertView == null) [英] ListView getView - if (convertView == null) not called on first scroll
问题描述
当记录首次出现在ListView上时，它们看起来不错，并且getView if (convertView == null)被正确调用，因为记录是首次可见的.
但是，即使我第一次滚动ListView，也不会调用if (convertView == null).因此，在滚动条上出现的第一项中，顶部项中的子项被重复.根据我的理解，如果第一次滚动ListView，则应调用if (convertView == null).
如果我错了，请纠正我.
getView:
When records first appear on ListView, they seem fine and the getView if (convertView == null) is called correctly as records are visible for the first time.
However, if I scroll the ListView, even for the first time, if (convertView == null) is not called. Because of which the child in top item is repeated in the first item which appears on scroll. As per my understanding, if the ListView is scrolled for the first time, if (convertView == null) should be called.
Please correct me if I am wrong.
getView :
@Override
public View getView(int position, View convertView, ViewGroup parent) {
try {
ViewHolder holder = null;
int rowType = getItemViewType(position);
if (convertView == null) {
holder = new ViewHolder();
switch (rowType) {
case TYPE_ITEM:
convertView = inflater.inflate(R.layout.activity_item, null);
activityModel = (truegroups.model.Activity) arrActivity.get(position);
holder.activityLayout = (RelativeLayout) convertView.findViewById(R.id.activity_item_layout);
holder.startDate = (TextView) convertView.findViewById(R.id.lblStartDate);
holder.line = (TextView) convertView.findViewById(R.id.lblLine);
holder.endDate = (TextView) convertView.findViewById(R.id.lblEndDate);
holder.groupName = (TextView) convertView.findViewById(R.id.lblGroupName);
holder.activity = (TextView) convertView.findViewById(R.id.lblActivity);
holder.location = (TextView) convertView.findViewById(R.id.lblLocation);
holder.topInviteeLayout = (RelativeLayout) convertView.findViewById(R.id.invitationTopPanel);
int iCount = 0;
for (Invitation invitation : activityModel.getArrInvitations()) {
ImageView imgTopStatus = new ImageView(activity);
RelativeLayout.LayoutParams imgStatusParams = new RelativeLayout.LayoutParams(40, 40);
imgStatusParams.setMarginStart(160);
imgStatusParams.setMargins(160, 20, 0, 0);
if (iCount > 0)
imgStatusParams.addRule(RelativeLayout.BELOW, holder.arrImageStatus.get(iCount - 1).getId());
imgTopStatus.setId(iCount * iCount + iCount + 1);
holder.topInviteeLayout.addView(imgTopStatus, imgStatusParams);
holder.arrImageStatus.add(imgTopStatus);
TextView topInviteeName = new TextView(activity);
RelativeLayout.LayoutParams topInviteeParams = new RelativeLayout.LayoutParams(300, ViewGroup.LayoutParams.WRAP_CONTENT);
topInviteeParams.addRule(RelativeLayout.RIGHT_OF, imgTopStatus.getId());
if (iCount > 0)
topInviteeParams.addRule(RelativeLayout.BELOW, holder.arrlblTopInviteeName.get(iCount - 1).getId());
topInviteeParams.setMargins(15, 5, 5, 15);
topInviteeName.setTextColor(Color.BLACK);
topInviteeName.setTextSize(14);
topInviteeName.setBackgroundColor(Color.WHITE);
topInviteeName.setId(iCount * iCount + 2 * iCount + 2);
//topInviteeName.setText(invitation.getChildName());
holder.topInviteeLayout.addView(topInviteeName, topInviteeParams);
holder.arrlblTopInviteeName.add(topInviteeName);
//topInviteeParams.addRule(RelativeLayout.ALIGN_TOP, imgTopStatus.getId());
// imgStatusParams.addRule(RelativeLayout.ALIGN_BASELINE, topInviteeName.getId());
Button decline = new Button(activity);
RelativeLayout.LayoutParams paramsDecline = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, 80);
paramsDecline.addRule(RelativeLayout.ALIGN_PARENT_RIGHT, RelativeLayout.TRUE);
if (iCount > 0)
paramsDecline.addRule(RelativeLayout.BELOW, holder.arrDecline.get(iCount - 1).getId());
decline.setTextColor(Color.BLACK);
decline.setTextSize(9);
decline.setText("Decline");
decline.setId(iCount * iCount + 3 * iCount + 3);
holder.topInviteeLayout.addView(decline, paramsDecline);
holder.arrDecline.add(decline);
Button accept = new Button(activity);
RelativeLayout.LayoutParams paramsAccept = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, 80);
if (iCount > 0)
paramsAccept.addRule(RelativeLayout.BELOW, holder.arrAccept.get(iCount - 1).getId());
paramsAccept.addRule(RelativeLayout.RIGHT_OF, topInviteeName.getId());
// paramsAccept.addRule(RelativeLayout.ALIGN_BOTTOM, decline.getId());
paramsAccept.setMarginStart(155);
accept.setTextColor(Color.BLACK);
accept.setTextSize(9);
accept.setId(iCount * iCount + 8 * iCount + 8);
accept.setText("Accept");
holder.topInviteeLayout.addView(accept, paramsAccept);
holder.arrAccept.add(accept);
paramsDecline.addRule(RelativeLayout.ALIGN_TOP, accept.getId());
iCount++;
}
break;
case TYPE_SEPARATOR:
convertView = inflater.inflate(R.layout.activity_header, null);
holder.header = (TextView) convertView.findViewById(R.id.textSeparator);
holder.headerWeek = (TextView) convertView.findViewById(R.id.textWeekNumber);
break;
}
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
if (arrActivity.size() <= 0) {
Log.d("Data", "No data found !!");
} else {
switch (rowType) {
case TYPE_ITEM:
activityModel = (truegroups.model.Activity) arrActivity.get(position);
//
holder.groupName.setText(activityModel.getGroupName());
holder.activity.setText(activityModel.getTitle());
holder.location.setText(activityModel.getLocation());
holder.startDate.setText(getHours(activityModel.getStartDate()));
holder.endDate.setText(getHours(activityModel.getEndDate()));
int iCount = 0;
for (Invitation invitation : activityModel.getArrInvitations()) {
ImageView imgStatus = holder.arrImageStatus.get(iCount);
//ImageView imgStatus = (ImageView) holder.topInviteeLayout.getChildAt(0);
if (invitation.getResponse().equals("3"))
imgStatus.setImageResource(R.drawable.notresponded);
else if (invitation.getResponse().equals("1"))
imgStatus.setImageResource(R.drawable.attending);
else
imgStatus.setImageResource(R.drawable.decline);
TextView inviteeName = holder.arrlblTopInviteeName.get(iCount);
//TextView inviteeName = (TextView) holder.topInviteeLayout.getChildAt(1);
inviteeName.setText(invitation.getChildName());
iCount++;
}
convertView.setOnClickListener(new OnItemClickListener(position));
break;
case TYPE_SEPARATOR:
holder.header.setText(getHeaderDate(String.valueOf(arrActivity.get(position))));
Calendar calendarGivenDate = Calendar.getInstance();
calendarGivenDate.set(Calendar.DAY_OF_MONTH, Integer.parseInt(String.valueOf(arrActivity.get(position)).split("/")[1]));
calendarGivenDate.set(Calendar.MONTH, Integer.parseInt(String.valueOf(arrActivity.get(position)).split("/")[0]));
calendarGivenDate.set(Calendar.YEAR, Integer.parseInt(String.valueOf(arrActivity.get(position)).split("/")[2]));
int weekNumber = calendarGivenDate.get(Calendar.WEEK_OF_YEAR);
holder.headerWeek.setText(StringUtils.join("WEEK ", String.valueOf(weekNumber)));
break;
}
}
return convertView;
} catch (Exception e) {
e.printStackTrace();
Toast.makeText(activity, e.getMessage(), Toast.LENGTH_LONG).show();
Log.d("Exception : ", e.getMessage());
return convertView;
}
}
推荐答案
由于ListView实现视图回收，因此永远不会出现convertView == null初始化后的情况.
Because the ListView implements view recycling, you should never get a case where convertView == null after it is initialized.
初始化ListView时，它将创建行并在它们上调用getView，直到屏幕上充满行.假设此数字是10行，编号为0-9，而第10行仅部分可见.向下滚动时，第0行将滚动到视图之外，并且新行需要在底部显示.而不是为第10行初始化一个新的内存块，而是占用第0行，并在您的getView()函数中将其提供给您.如果不修改这些值，它将再次显示在列表的底部，所有原始值都位于第0行.在此示例中，只有在您获得null的convertView时，才是正在使用多种类型的对象(例如分隔符)，因此滚动实际上需要在上一行滚动出屏幕之前创建新行.
When you intialize the ListView, it creates rows and calls getView on them until the screen is full of rows. Suppose this number is 10 rows, numbered 0-9, and the 10th row is only partially visible. When you scroll down, row 0 is scrolled out of view, and a new row needs to show up on the bottom. Instead of initializing a new block of memory for row 10, instead it takes row 0 and gives it to you in your getView() function. If you don't modify the values, it will show up once again on the bottom of the list, with all of the original values of row 0. In this example, the only time you'll get a null convertView, is if you're using multiple types of objects (like a separator), and the scrolling actually needs to create a new row before the previous row scrolls off the screen.
因此，如果converView为null，则需要首先创建一行，但与此不同的是，之后需要(重新)初始化视图内的所有值.
Thus you need to first create a row if the converView is null, but separately from that you need to (re)initialize all of the values inside the view afterwards.
编写getView函数的最佳策略遵循以下基本结构:
The best strategy for writing a getView function follows this basic structure:
if (convertView == null) {
convertView = new WhateverViewTypeYouNeed();
}
if (convertView != SEPARATOR) {
initializeValues();
}
return convertView;
您可以查看此链接以了解更多信息阅读.
You can see this link for further reading.
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