如何在 uitableview for IOS 中使用可重用单元 [英] How to use Reusable Cells in uitableview for IOS

问题描述

好的.我似乎无法对 tableviews 的工作方式有一个坚定的理解.有人可以向我解释一下如何在表格视图中重用单元格，尤其是在滚动时?我对此的主要痛点之一是，当我在一个单元格中创建一个动作时，当我滚动时其他单元格会受到影响.我尝试使用数组作为模型的后端，但我仍然得到了不应该改变的单元格.很难弄清楚为什么当数组中的模型没有改变时它们会改变.

Ok. I cant seem to get a firm understanding on how tableviews work. Would someone please explain to me how cells are reused in tableviews especially when scrolling? One of the major pain points I have about this is the fact that when I create an action in one cell, other cells are affected when I scroll. I tried using an array as the backend for the model but still I get cells that change when not suppose to. The hard thing to figure out is why do they change when the the model in the array is not changed.

一个简单的例子:

带有喜欢"按钮的表格视图单元格.当我单击其中一个单元格中的按钮时，按钮文本变为不喜欢"(到目前为止一切都很好).但是当我向下滚动时，即使我没有选择它们，其他单元格也会显示不像".当我向上滚动时，我最初选择的单元格会再次更改，并且更新的单元格也会更改.

table view cells with the button "like". When I click the button in one of the cells, the button text changes to "Unlike"(So far so good). But When I scroll down, other cells also show "Unlike" even though I haven't selected them. And when I scroll up, the cells I originally selected change again and newer ones are changed as well.

我似乎无法弄清楚这一点.如果你能给我看一个工作示例源代码，那就太棒了！！！谢谢！

I cant seem to figure this out. If you can show me a working example source code, that would be awesome!!! Thanks!

- (void)viewDidLoad
{
    [super viewDidLoad];


    likeState = [[NSMutableArray alloc]init];

    int i =0;
    for (i=0; i<20; i++) {
        [likeState addObject:[NSNumber numberWithInt:0]];
    }
} 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell" forIndexPath:indexPath];

    UIButton *myButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [myButton setTitle:@"Like" forState:UIControlStateNormal];
    [myButton addTarget:self action:@selector(tapped:) forControlEvents:UIControlEventTouchUpInside];
    myButton.frame = CGRectMake(14.0, 10.0, 125.0, 25.0);
    myButton.tag =indexPath.row;
    [cell.contentView addSubview:myButton];

    if (cell ==nil) {


    }

    if ([[likeState objectAtIndex:indexPath.row]boolValue]==NO) {
        [myButton setTitle:@"Like" forState:UIControlStateNormal];

    }
    else{
        [myButton setTitle:@"Unlike" forState:UIControlStateNormal];


    }


    return cell;
}
-(void)tapped:(UIButton *)sender{

[likeState replaceObjectAtIndex:sender.tag withObject:[NSNumber numberWithInt:1]];

    [sender setTitle:@"Unlike" forState:UIControlStateNormal];

}

推荐答案

我假设您是通过 Storyboard 执行此操作的，因为您还没有通过 Interface Builder<创建按钮/code>，您需要检查正在重复使用的单元格是否已经有按钮.
根据您当前的逻辑，每次单元格重新出现时，您都会创建一个新的按钮实例.

I am assuming you are doing this via Storyboard and since you haven't created your button via the Interface Builder, you need to check if the cell that is being re-used already has the button or not.
As per your current logic, you are creating a new button instance ever time the cell reappears.

我建议如下:

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

    //following is required when using XIB but not needed when using Storyboard
    /*
     if (cell == nil) {
         cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
     }
     */
    //Reason:
    //[1] When using XIB, dequeueReusableCellWithIdentifier does NOT create a cell so (cell == nil) condition occurs
    //[2] When using Storyboard, dequeueReusableCellWithIdentifier DOES create a cell and so (cell == nil) condition never occurs

    //check if cell is being reused by checking if the button already exists in it
    UIButton *myButton = (UIButton *)[cell.contentView viewWithTag:100];

    if (myButton == nil) {
        myButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [myButton setFrame:CGRectMake(14.0,10.0,125.0,25.0)];
        [myButton setTag:100]; //the tag is what helps in the first step
        [myButton setTitle:@"Like" forState:UIControlStateNormal];
        [myButton setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
        [myButton addTarget:self action:@selector(tapped:andEvent:) forControlEvents:UIControlEventTouchUpInside];
        [cell.contentView addSubview:myButton];

        NSLog(@"Button created");
    }
    else {
        NSLog(@"Button already created");
    }

    if ([likeState[indexPath.row] boolValue]) {
        [myButton setTitle:@"Unlike" forState:UIControlStateNormal];
    }
    else {
        [myButton setTitle:@"Like" forState:UIControlStateNormal];
    }

    return cell;
}

<小时>

-(void)tapped:(UIButton *)sender andEvent:(UIEvent *)event
{
    //get index
    NSSet *touches = [event allTouches];
    UITouch *touch = [touches anyObject];
    CGPoint currentTouchPosition = [touch locationInView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:currentTouchPosition];

    //toggle "like" status
    if ([likeState[indexPath.row] boolValue]) {
        [likeState replaceObjectAtIndex:indexPath.row withObject:@(0)];
        [sender setTitle:@"Like" forState:UIControlStateNormal];
    }
    else {
        [likeState replaceObjectAtIndex:indexPath.row withObject:@(1)];
        [sender setTitle:@"Unlike" forState:UIControlStateNormal];
    }
}

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