循环中的日期-显示第一个/跳过其余的[关闭]

Question

聊天具有来自 SQL 数据库的消息日期。时间戳用php日期格式化：

 $dateabove = date("d.m.Y : H:i",$row['message_time']);

日期在循环中（while）：-

今天必须显示今天，昨天必须显示昨天。然后只有日期来了。 它应该类似于 Whatsapp。

示例：- （$dateabove - $row['message_text']）：

me: 28.10.2020 : 13:75  - Hello

you: 28.10.2020 : 14:01  - Hello

me: 31.10.2020 : 11:01  - How are you?

you: 31.10.2020 : 12:01  - fine

me: 01.11.2020 : 10:05  -  Where you from?

应该看起来像：

*28.10.2020*

me: 28.10.2020 : 13:75  - Hello

you: 28.10.2020 : 14:01  - Hello


*Yesterday*

me: 31.10.2020 : 11:01  - How are you?

you: 31.10.2020 : 12:01  - fine


*Today*

me: 01.11.2020 : 10:05  -  Where you from?

问题是，如何只在循环中的第一条消息上方显示日期，而不在当天的后续消息中显示日期。

这就是我的循环的样子：

while ($row = $db->sql_fetchrow($result));

for ($i = 0, $size = sizeof($rowset); $i < $size; $i++)
{
echo $row['message_time']);
}

Answer 1

这里有一个可能的方法的小演示。请阅读 cmets 以获取有关正在发生的事情的详细说明。有关现场演示，请参阅 this eval。你可以玩弄它，你可以看到它的输出。

<?php

// Current time as UNIX timestamp.
$now = time();
// Find yesterday's date by subtracting one day ('P1D') from today (new DateTime).
$yesterday = (new DateTime)->sub(new DateInterval('P1D'));

// Mock a bunch of messages.
$messages =
[
    // Yesterday's messages
    [
        'user_id' => 1,
        'user_natural_name' => 'me',
        // format('U') will give us UNIX timestamp.
        'timestamp' => $yesterday->setTime(19, 0)->format('U'),
        'text' => 'Hiya'
    ],
    [
        'user_id' => 2,
        'user_natural_name' => 'you',
        'timestamp' => $yesterday->setTime(19, 5)->format('U'),
        'text' => 'Hey, how are you?'
    ],
    
    // Today's messages
    [
        'user_id' => 1,
        'user_natural_name' => 'me',
        'timestamp' => $now,
        'text' => 'Hello'
    ],
    [
        'user_id' => 2,
        'user_natural_name' => 'you',
        // Three seconds later.
        'timestamp' => $now + 3,
        'text' => 'Hi'
    ],
    [
        'user_id' => 1,
        'user_natural_name' => 'me',
        'timestamp' => $now + 6,
        'text' => 'What\'s up'
    ],
    [
        'user_id' => 2,
        'user_natural_name' => 'you',
        'timestamp' => $now + 9,
        'text' => 'Not much'
    ],
    [
        'user_id' => 1,
        'user_natural_name' => 'me',
        'timestamp' => $now + 12,
        'text' => 'Awesome'
    ]
];

// If $lastWindowDate differs from the current message in the queue,
// then display it as a separator between day-to-day conversations.
$lastWindowDate = NULL;

// $index will tell us whether we already had output from earlier days so we can
// show a separating newline.
foreach ($messages as $index => $message)
{
    // Window as a perspective on the message flow.
    $windowDate = date('Ymd', $message['timestamp']);
    // If current message's date is not last message's date, then output it to the user.
    if ($windowDate !== $lastWindowDate)
    {
        // Translate today's YMD and yesterday's YMD to something more naturally interpretable for a better UX.

        // Compare against current message's datestamp.
        switch (date('Ymd', $message['timestamp']))
        {
            // date('Ymd') without a second argument defaults to 'today'.
            case date('Ymd'):
                $dateLabel = 'today';
            break;
            // Format $yesterday DateTime as Ymd.
            case $yesterday->format('Ymd'):
                $dateLabel = 'yesterday';
            break;
            // Neither? Pass through as numeric date.
            default:
                $dateLabel = $windowDate;
            break;
        }
        
        // Already had previous output? Show a newline now as visual separator.
        if ($index)
            echo "\n";

        // Output date label at the top of message list for that day.
        echo "$dateLabel\n";
        
        // Reset the last date seen for the conditional to work.
        $lastWindowDate = $windowDate;
    }
 
    // Show message.   
    echo "{$message['user_natural_name']}: " . date('d.m.Y : H:i', $message['timestamp']) . " - {$message['text']}\n";
}