iOS中NSMutableArray没有对象时应用崩溃

Question

I have four textfields like textfield1 , textfield2 , textfield3 , textfield4 and one button. When I click on the button I am adding the textfield text to an NSMutableArray and populating in a tableview .

My code is:

- (void)buttonClick
{
    NSMutableArray  *array =[[NSMutableArray alloc]init];
    [array addObject: textfield1.text];
    [array addObject: textfield2.text];
    [array addObject: textfield3.text];
    [array addObject: textfield4.text];
 }

Populating in table view using delegate methods

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [array count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }

    cell.textLabel.text =[array objectAtIndex:indexPath.row];
    return cell;
}

The above code is working fine. But when I click on button without entering any data in the textfields, the app is crashing because the array is empty. How to solve this problem?

Answer 1

You can't add nil to an array.

[array addObject:textfield1.text ?: @""];
[array addObject:textfield2.text ?: @""];
[array addObject:textfield3.text ?: @""];
[array addObject:textfield4.text ?: @""];

This makes sure there are four items in the array (possibly empty strings).

Answer 2

Why crashes?

You can't add nil in array. It should have something inside of it.

-(void)buttonClick
{
    NSMutableArray  *array =[[NSMutableArray alloc]init];

    if ([textfield1.text length]>0) {
        [array addObject: textfield1.text];

    }
    if ([textfield2.text length]>0) {
        [array addObject: textfield2.text];

    }
    if ([textfield3.text length]>0) {
        [array addObject: textfield3.text];
    }



}

Answer 3

Try this

-(void)buttonClick
{
    NSMutableArray  *array =[[NSMutableArray alloc]init];
     if(textfield1.text.length > 0)
        [array addObject: textfield1.text];

     if(textfield2.text.length > 0)
        [array addObject: textfield2.text];

     if(textfield3.text.length > 0)
        [array addObject: textfield3.text];

    if(textfield4.text.length > 0)
        [array addObject: textfield4.text];

 }

Populating in table view using delegate methods

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [array count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {
        cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }
    cell.textLabel.text =[array objectAtIndex:indexPath.row];
    return cell;
}

if you have multiple text fields then: //give tag value of each textfield from 100 to 150 or any any tag (i am considering 50 text fields)

for (int i=100; i<=150; i++) {
// self.view or use ur view on which u r addding textfield
    id txtF = [self.view viewWithTag:i]; 
    if([txtF isKindOfClass:[UITextField class]]) {
        UITextField *txtField = (UITextField*)txtF;
        if(txtField.text.length > 0) {
            //Add ur object
        }
    }
}

Answer 4

您可以先检查文本字段，然后再放置是否有文本的数组，如果是，则仅在数组中放置文本。

Answer 5

This line in the buttonClick method defined a local array variable:

NSMutableArray  *array =[[NSMutableArray alloc]init];

It should be

array =[[NSMutableArray alloc]init];

Which is your instance variable array.