滚动UITableView时UITableViewCell的位置更改

Question

My UITableViewCell position changed while scroll UITableView . Here i have more UITableViewCell . So it covers more than one page screen. When i scroll top to bottom the position of UITableViewCell is changed such like 1st cell went 5th. And 2nd cell came to 1st and etc.

My Code:

    - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:
(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"SignUpWithEmailCell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

if (cell == nil)
{
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    cell.backgroundColor = [UIColor clearColor];
    cell.selectionStyle = UITableViewCellSelectionStyleNone;

    switch (indexPath.row) {

        case 0: {

            UILabel *lblFirstName = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 100, 40)];
            lblFirstName.text = @"First Name";
            [cell.contentView addSubview:lblFirstName];

            self.txtFirstName = [[UITextField alloc]initWithFrame:CGRectMake(lblFirstName.frame.origin.x + lblFirstName.frame.size.width + 5, 0, 190, 40)];
            self.txtFirstName.delegate = self;
            self.txtFirstName.text = strFirstName;
            self.txtFirstName.tag = 0;
            self.txtFirstName.userInteractionEnabled = YES;
            self.txtFirstName.font = [UIFont systemFontOfSize:15.0];
            self.txtFirstName.clearButtonMode = UITextFieldViewModeWhileEditing;
            self.txtFirstName.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
            [cell.contentView addSubview:self.txtFirstName];
            break;
        } case 1: {

            UILabel *lblLastName = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 100, 40)];
            lblLastName.text = @"Last Name";
            [cell.contentView addSubview:lblLastName];

            self.txtLastName = [[UITextField alloc]initWithFrame:CGRectMake(lblLastName.frame.origin.x + lblLastName.frame.size.width + 5, 0, 190, 40)];
            self.txtLastName.backgroundColor = [UIColor clearColor];
            self.txtLastName.delegate = self;
            self.txtLastName.tag = 1;
            self.txtLastName.text = strLastName;
            self.txtFirstName.userInteractionEnabled = YES;
            self.txtLastName.returnKeyType = UIReturnKeyDone;
            self.txtLastName.clearButtonMode = UITextFieldViewModeWhileEditing;
            self.txtLastName.font = [UIFont systemFontOfSize:15.0];
            self.txtLastName.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
            [cell.contentView addSubview:self.txtLastName];
            break;
        }
        default:
            break;
    }
}

 return cell;
}

Could anyone guide me to archive it correctly..

Thanks in Advance.

Answer 1

You must set the visual elements of the cell even when cell is not nil. If you read the documentation, you will notice that Apple says that the cell's content must always be updated in this method. The reason is because checking for nil just tests if you must create a new cell. If you don't need to create a new cell, that means you are reusing a cell, and therefore it will most likely display contents from a row other than the one you intended. Therefore, you should reset the contents every time in this method.

From this document :

The table view's data source implementation of tableView:cellForRowAtIndexPath: should always reset all content when reusing a cell.

Here's some code to get you started... but it will need to be improved since you are adding subviews to the cells in this method. That should only happen when the cell is nil, and you should store a reference to those subviews so that they can be accessed at other times.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:
(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"SignUpWithEmailCell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
        cell.backgroundColor = [UIColor clearColor];
        cell.selectionStyle = UITableViewCellSelectionStyleNone;
    }

    switch (indexPath.row) {

        case 0: {

            UILabel *lblFirstName = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 100, 40)];
            lblFirstName.text = @"First Name";
            [cell.contentView addSubview:lblFirstName]; // TODO: MUST BE MOVED

            self.txtFirstName = [[UITextField alloc]initWithFrame:CGRectMake(lblFirstName.frame.origin.x + lblFirstName.frame.size.width + 5, 0, 190, 40)];
            self.txtFirstName.delegate = self;
            self.txtFirstName.text = strFirstName;
            self.txtFirstName.tag = 0;
            self.txtFirstName.userInteractionEnabled = YES;
            self.txtFirstName.font = [UIFont systemFontOfSize:15.0];
            self.txtFirstName.clearButtonMode = UITextFieldViewModeWhileEditing;
            self.txtFirstName.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
            [cell.contentView addSubview:self.txtFirstName]; // TODO: MUST BE MOVED
            break;
        } case 1: {

            UILabel *lblLastName = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 100, 40)];
            lblLastName.text = @"Last Name";
            [cell.contentView addSubview:lblLastName]; // TODO: MUST BE MOVED

            self.txtLastName = [[UITextField alloc]initWithFrame:CGRectMake(lblLastName.frame.origin.x + lblLastName.frame.size.width + 5, 0, 190, 40)];
            self.txtLastName.backgroundColor = [UIColor clearColor];
            self.txtLastName.delegate = self;
            self.txtLastName.tag = 1;
            self.txtLastName.text = strLastName;
            self.txtFirstName.userInteractionEnabled = YES;
            self.txtLastName.returnKeyType = UIReturnKeyDone;
            self.txtLastName.clearButtonMode = UITextFieldViewModeWhileEditing;
            self.txtLastName.font = [UIFont systemFontOfSize:15.0];
            self.txtLastName.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
            [cell.contentView addSubview:self.txtLastName]; // TODO: MUST BE MOVED
            break;
        }
        default:
            break;
    }


 return cell;
}

Answer 2

这是您的问题， if (cell == nil)第一次使该单元格为零，那么我将创建一个单元格，那么我会尝试重用de cell单元格为非null，因此我像以前一样添加此单元格，而没有进行任何更改，为了解决您的问题，您必须删除if和for no donage更好的方法是创建一个包含所有对象的自定义单元格。

Answer 3

To optimize the memory iOS initializes and uses only screen displayed cells. When you scroll to see next content it dequeues the non-visible cell and uses it for new visible cell. So, 1st cell is used at 8th row and so on. Now, in your code, you are not resetting the content when this dequeue operation is happening. All your cell content code is only when cell is not there. Take out the cell initializing code from your IF condition and you should be good to go.