小编sco*_*ear的帖子

我试图检测片段在滑动视图上何时可见，以便在其可见时更新其内容。我是这样做的。

public class MyFragment extends Fragment {
  @Override
  public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (isVisibleToUser) { }
    else {  }
  }
}

问题是，当我转到该页面时，它会很好地工作，但是当我在选项卡中选择该页面时，它会崩溃“尝试调用虚拟方法”。

请帮我，谢谢

我有一个主要活动，然后每个片段都有一个活动。

主要：

public class Principal extends ActionBarActivity implements ActionBar.TabListener {

SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_principal);

    // Set up the action bar.
    final ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Create the adapter that will return a fragment …

我正在尝试从名为“ producers”的表中获取所有记录，但出现以下错误。

Missing argument 1 for Illuminate\Support\Collection::get(), called in /var/www/html/wines/storage/framework/views/ac350063efb624ac50d199628897fd7d72bc196c.php on line 63 and defined (View: /var/www/html/wines/resources/views/admin/producers.blade.php)

这是我的文件：（迁移）

<?php
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateProducerTable extends Migration    {
    public function up()
    {
        Schema::create('producers', function (Blueprint $table) {
            $table->increments('id');
            $table->string('producer_name');
            $table->string('phone_number');
            $table->string('user_id')->unique();
            $table->string('avatar')->default('default.jpg');
            $table->timestamps();
        });
    }
    public function down()
    {
        Schema::drop('producers');
    }
}

我的ProducerController

<?php
namespace App\Http\Controllers;
use Illuminate\Http\Request;
use App\Http\Requests;
class ProducerController extends Controller    {
    public function __construct()        {
        $this->middleware('isProducer');
    }    }

生产者模型：

<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class Producer …