从 JSON 字符串中提取数据时出现未定义的属性错误？答案

【问题标题】：Get undefined property error while extracting data from JSON string?从 JSON 字符串中提取数据时出现未定义的属性错误？
【发布时间】：2015-04-17 07:24:29
【问题描述】：

我有以下 JSON 字符串

{
"data": [
{
  "id": "533513150124231",
  "created_time": "2015-02-27T05:23:02+0000",
  "photos": {
    "data": [
      {
        "images": [
          {
            "height": 667,
            "source": "https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/10418414_555711037904442_8567793956228056677_n.jpg?oh=a8815f978e43abb98ab229cf83c85264&oe=559AB81A&__gda__=1440316102_f98baa62cfba9d6f94cd327f682ffd25",
            "width": 460
          },
          {
            "height": 464,
            "source": "https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/p320x320/10418414_555711037904442_8567793956228056677_n.jpg?oh=d35e77306662faecf87e744605d307bd&oe=559A52BE&__gda__=1436229856_60f872b53adcbf8aa302903fb019b327",
            "width": 320
          },
          {
            "height": 540,
            "source": "https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/p180x540/10418414_555711037904442_8567793956228056677_n.jpg?oh=b759bdb9362c6bfee5aa2709928d8f69&oe=559CEC03&__gda__=1436252765_64a5b0e1c663efead53300007c437990",
            "width": 372
          },
          {
            "height": 188,
            "source": "https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/p130x130/10418414_555711037904442_8567793956228056677_n.jpg?oh=cde013e3d7e9b2433e57b66e33167d92&oe=55A6CED1&__gda__=1436392591_2d5580f28f551316f45bc3930c459386",
            "width": 130
          },
          {
            "height": 225,
            "source": "https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/p75x225/10418414_555711037904442_8567793956228056677_n.jpg?oh=a5caf9c528ba7a8f8380db27d42f82c0&oe=55E49852&__gda__=1436028283_98c7a7d639ed37620f3a9b0fbb78472e",
            "width": 155
          }
        ],
        "created_time": "2015-04-17T06:00:00+0000",
        "id": "555711037904442"
      }
    ],
    "paging": {
      "cursors": {
        "before": "NTU1NzExMDM3OTA0NDQy",
        "after": "NTU1NzExMDM3OTA0NDQy"
      },
      "next": "https://graph.facebook.com/v2.3/533513150124231/photos?pretty=0&fields=images&limit=1&after=NTU1NzExMDM3OTA0NDQy"
    }
  }
},
{
  "id": "533911933417686",
  "created_time": "2015-02-28T07:18:09+0000",
  "photos": {
    "data": [
      {
        "images": [
          {
            "height": 960,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/11156332_555538204588392_7524203027467514208_n.jpg?oh=472d4dc677b7c6a1358bf59392071039&oe=55A97829&__gda__=1436014225_b6c761b77d7659f3499c98fa870efdd7",
            "width": 960
          },
          {
            "height": 720,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p720x720/11156332_555538204588392_7524203027467514208_n.jpg?oh=e9a1b55146bf65d1779fcfabe063012e&oe=55D62F58&__gda__=1437234622_80c2bf1dbec64f6851b15b9d33084b21",
            "width": 720
          },
          {
            "height": 600,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p600x600/11156332_555538204588392_7524203027467514208_n.jpg?oh=0126ec5adea74e13252a3bafaba14a02&oe=55A67B37&__gda__=1440779729_3645ddf066d0158821f83f8ea077b05f",
            "width": 600
          },
          {
            "height": 480,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p480x480/11156332_555538204588392_7524203027467514208_n.jpg?oh=2d60610a0e588be12333f1c89d9a2317&oe=559A8CD7&__gda__=1435982897_782ac7a2cc1c6cafac63aaef4a29ae4f",
            "width": 480
          },
          {
            "height": 320,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p320x320/11156332_555538204588392_7524203027467514208_n.jpg?oh=4148aaca5b81862a626b5399db291ba9&oe=559F338D&__gda__=1440297579_389092cfce5f8aafef4573968409e819",
            "width": 320
          },
          {
            "height": 540,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p180x540/11156332_555538204588392_7524203027467514208_n.jpg?oh=d4f772948708181ba7004e7f324988c9&oe=55E13930&__gda__=1436695254_4f2c082572f0241510ab59504fadfc3e",
            "width": 540
          },
          {
            "height": 130,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p130x130/11156332_555538204588392_7524203027467514208_n.jpg?oh=e095b6eaa807792afbfeaa2ed85f276b&oe=55A501E2&__gda__=1437193220_18d71223bd95cf5cba2542a11c24d18e",
            "width": 130
          },
          {
            "height": 225,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p75x225/11156332_555538204588392_7524203027467514208_n.jpg?oh=8e3f487af88e40470b93073853e3e8c7&oe=55A95661&__gda__=1436678326_211dc38936f310d46801ffea0582a646",
            "width": 225
          }
        ],
        "created_time": "2015-04-16T16:40:57+0000",
        "id": "555538204588392"
      }
    ],
    "paging": {
      "cursors": {
        "before": "NTU1NTM4MjA0NTg4Mzky",
        "after": "NTU1NTM4MjA0NTg4Mzky"
      },
      "next": "https://graph.facebook.com/v2.3/533911933417686/photos?pretty=0&fields=images&limit=1&after=NTU1NTM4MjA0NTg4Mzky"
    }
  }
},
{
  "id": "533471226795090",
  "created_time": "2015-02-27T03:20:20+0000",
  "photos": {
    "data": [
      {
        "images": [
          {
            "height": 252,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/10384022_533471210128425_1090655257311798538_n.png?oh=42293c184f93099fed226845661e68ba&oe=55A8A0BC&__gda__=1440376580_7355eccec9a71b9c1b1c3fb08b7c438d",
            "width": 785
          },
          {
            "height": 130,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p130x130/10384022_533471210128425_1090655257311798538_n.png?oh=61e2595ba9367c63ce4c31272d2f5965&oe=55E1AE77&__gda__=1440510353_4d66bcf977355eb4514d6ef5b665f496",
            "width": 404
          },
          {
            "height": 225,
            "source": "https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/p75x225/10384022_533471210128425_1090655257311798538_n.png?oh=331aad239450d4f3d7f6984bae23a2e6&oe=55E237F4&__gda__=1440632867_d90a8c45baa7d4d4cdaa87346095b863",
            "width": 700
          }
        ],
        "created_time": "2015-02-27T03:20:21+0000",
        "id": "533471210128425"
      }
    ],
    "paging": {
      "cursors": {
        "before": "NTMzNDcxMjEwMTI4NDI1",
        "after": "NTMzNDcxMjEwMTI4NDI1"
      }
    }
  }
},
{
  "id": "533470536795159",
  "created_time": "2015-02-27T03:16:54+0000",
  "photos": {
    "data": [
      {
        "images": [
          {
            "height": 320,
            "source": "https://scontent.xx.fbcdn.net/hphotos-xfa1/v/t1.0-9/10431515_533470543461825_4940061426497683241_n.jpg?oh=b7c513e31c9dc4da9e64df4094280a70&oe=559D578E",
            "width": 240
          },
          {
            "height": 173,
            "source": "https://scontent.xx.fbcdn.net/hphotos-xfa1/v/t1.0-9/p130x130/10431515_533470543461825_4940061426497683241_n.jpg?oh=d4d3e16d0cc7b43e9ae44df494f08e29&oe=55D70A45",
            "width": 130
          },
          {
            "height": 225,
            "source": "https://scontent.xx.fbcdn.net/hphotos-xfa1/v/t1.0-9/p75x225/10431515_533470543461825_4940061426497683241_n.jpg?oh=5d8e3097a633df2c9ca86de0be65622f&oe=5599C4C6",
            "width": 168
          }
        ],
        "created_time": "2015-02-27T03:16:55+0000",
        "id": "533470543461825"
      }
    ],
    "paging": {
      "cursors": {
        "before": "NTMzNDcwNTQzNDYxODI1",
        "after": "NTMzNDcwNTQzNDYxODI1"
      }
    }
  }
}
],
"paging": {
"cursors": {
  "after": "NTMzNDcwNTM2Nzk1MTU5",
  "before": "NTMzNTEzMTUwMTI0MjMx"
}
}
}

我从 Facebook Graph API explorer 获得了这个字符串。之后，我尝试从这个 JSON 数据中提取图像源。这是我写的代码。

$output = 'All the JSON data above is written here';
$output = json_decode($output);

for($i=0;$i<2;$i++)
{
$image = $output->photos->data->images[$i][0]->source;
echo $image.'</br>';
}

使用此代码我得到以下错误

 Undefined property: stdClass::$photos on line 1796
 Trying to get property of non-object on line 1796

我想像这样提取每个类别中第一张图片的来源

https://www.facebook.com/l.php?u=https%3A%2F%2Fscontent.xx.fbcdn.net%2Fhphotos-xfa1%2Fv%2Ft1.0-9%2F10431515_533470543461825_4940061426497683241_n.jpg%3Foh%3Db7c513e31c9dc4da9e64df4094280a70%26oe%3D559D578E&h=8AQE_FhcA

【问题讨论】：

标签： php arrays json

【解决方案1】：

我建议使用foreach 替代。你也可以用它来遍历解码后的JSON：

foreach($output->data as $data) {
    $photos = $data->photos->data[0]->images;
    foreach($photos as $img) {
        echo "{$img->source} <br/>";
    }
}

顺便说一句，它遍历所有源批次，你想要第一个，你可以使用reset 获取当前批次的第一个，然后指向属性：

foreach($output->data as $data) {
    $photos = $data->photos->data[0]->images;
    $first = reset($photos)->source;
    echo "{$first} <br/>";
}

【讨论】：

我使用$data->photos->data[0]->images[0]->source 来获取第一张图片。它会给我错误的结果吗？
@SandipPatel 不，它也一样，我只是在这个例子中使用reset，直接将它指向索引0 也可以正常工作

【解决方案2】：

尝试跟随你的 json 树。改变 $image = $output->photos->data->images[$i][0]->source; 到 $image = $output->data->photos->data->images[$i][0]->source;

【讨论】：

我仍然收到Trying to get property of non-object这个错误。