Why are we checking if (cell == nil) in a UITableViewController?

I am trying to implement a UITableView based application. To do this, I select UITableViewStyle - Group.In my TableView is section 15 , each section has 1 row.

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 15; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return 1; } -(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath { if (indexPath.section==12) { return 120; } else { return 60; } } 

I want to add a UITextView to section 12

For this, I made the following code

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; } if ([indexPath section] == 12) { if([indexPath row]==0) { descriptionTextField=[[UITextView alloc] initWithFrame:CGRectMake(5, 8, 290, 106)]; descriptionTextField.font = [UIFont systemFontOfSize:15.0]; descriptionTextField.backgroundColor=[UIColor scrollViewTexturedBackgroundColor]; [descriptionTextField setDelegate:self]; [descriptionTextField setTag:2]; [descriptionTextField setText:@"Enter Location Description."]; descriptionTextField.keyboardType=UIKeyboardTypeDefault; descriptionTextField.returnKeyType=UIReturnKeyNext; descriptionTextField.textColor=[UIColor blackColor]; descriptionTextField.editable=YES; descriptionTextField.autocapitalizationType=UITextAutocapitalizationTypeWords; descriptionTextField.autocorrectionType=UITextAutocorrectionTypeDefault; descriptionTextField.textAlignment=UITextAlignmentLeft; UIToolbar* keboardToolBar=[[UIToolbar alloc]initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, 32)]; UIBarButtonItem *extra=[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil]; UIBarButtonItem *Done=[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(keyboardDoneButtonActin:)]; [Done setWidth:65.0f]; [keboardToolBar setItems:[[[NSArray alloc]initWithObjects:extra,Done, nil]autorelease] ]; [extra release]; [Done release]; [keboardToolBar setTintColor:[UIColor blackColor]]; [keboardToolBar setAlpha:.70]; [descriptionTextField setInputAccessoryView:keboardToolBar]; [descriptionTextField setTag:101]; [cell.contentView addSubview:descriptionTextField]; [descriptionTextField release]; } } return cell; } 

At the initil stage, a table view like this

enter image description here

if I scroll the table up and down, then the uitextView section has changed and will display several places.

enter image description here

I can’t understand my mistake, why did this happen?

if I implement the above code as if (cell == nil)

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; if ([indexPath section] == 12) { if([indexPath row]==0) { **/* implemention all code here*/** [cell.contentView addSubview:descriptionTextField]; [descriptionTextField release]; } } return cell; 

}

UITextView is not suitable, I think it does not allocate.

so what is the difference between embedding code in if (cell == nil) {inside}

if (cell == nil) {} side

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2 answers
 NSString *CellIdentifier = [NSString stringWithFormat:@"%i",indexPath.row]; // Dequeue or create a cell of the appropriate type. UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 

It can be used instead

 static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 

this is a simple example for writing inside a cell == nill

 - (UITableViewCell *)tableView:(UITableView *)tableView1 cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"CellIdentifier"; // Dequeue or create a cell of the appropriate type. UITableViewCell *cell = [tableView1 dequeueReusableCellWithIdentifier:CellIdentifier]; cell= nil; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; [[cell.contentView viewWithTag:100+indexPath.row] removeFromSuperview]; UIView *selectview = [[UIView alloc]initWithFrame:CGRectMake(0, 0, cell.frame.size.width, 30)]; [selectview setBackgroundColor:[UIColor colorWithPatternImage:[UIImage imageNamed:@"strip_s12A-1_h.png"]]]; cell.selectedBackgroundView = selectview; [selectview release]; UILabel *cellTitle=[[UILabel alloc]initWithFrame:CGRectMake(40, 0, 300, 30)]; //cellTitle.adjustsFontSizeToFitWidth=YES; [cellTitle setBackgroundColor:[UIColor clearColor]]; [cellTitle setFont:[UIFont fontWithName:@"Arial Rounded MT Bold" size:17]]; [cellTitle setTextColor:[UIColor blackColor]]; cellTitle.tag = 100+indexPath.row; cellTitle.text= [[[cellArray objectAtIndex:indexPath.section]objectAtIndex:indexPath.row] valueForKey:@"Des2"]; [cell.contentView addSubview:cellTitle]; [cellTitle release]; } return cell; } 

I think there will be enough right

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The if (cell == nil) test handles the case where there are no reusable cells to remove from the queue, in which case you must create a new cell. When you create a new cell, you are responsible for building your hierarchy of views.

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Source: https://habr.com/ru/post/910697/


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