Android - ListView 未显示在新活动中

Question

我对 Android 和面向对象的代码还很陌生，所以我可能会忽略一些小问题。

我有一个Activity，其中包含Fragments 中的一些自定义ListViews，通过滑动和标签更改。按下特定列表中的特定项目几次后，应该会打开一个新的 Activity 并包含另一个 ListView。

当我运行我的代码时，我可以从我的 Fragment (StatusFragment.java) 打开第二个 Activity (FactoryScreen.java)，但是 FactoryScreen.java 显示为空白 Activity。

我一直在网上论坛中搜索类似案例，但没有任何运气。同样，由于我是新手，所以我不完全确定调试方法。但是，我注意到包含 Activity 布局的fragment_factory_screen.xml 完全可以显示TextView 项目（带有基本的“Hello world”），但显然不是ListView。

StatusFragment.java（FactoryScreen.java 通过 Intent 从这里初始化）

    import java.util.ArrayList;

    import com.example.path.R;

    import android.content.Context;
    import android.content.Intent;
    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.AdapterView;
    import android.widget.ListView;
    import android.widget.Toast;

    public class StatusFragment extends Fragment
    {
         private Context mContext;
         private ArrayList<DataItem> data = new ArrayList<DataItem>(); // DataItem contains two strings
         ListView myList;
         int i = 0;

         @Override
         public void onCreate (Bundle savedInstanceState)
         {    
              super.onCreate(savedInstanceState);

              mContext = getActivity(); // Get the context of the Activity and therefore the fragment
              myList = new ListView (mContext); // Create a ListView

              // Fill out elements to go into 'data'
              ...
              // data.add each DataItem variable
              ...
          }

          @Override
          public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
          {
               // Inflate the view
               View rootView = inflater.inflate(R.layout.fragment_status, container, false);

               // (?) Identify myList to be a list to be placed in rootView
               myList=(ListView) rootView.findViewById(android.R.id.list);
               // Create and set the customised adapter to take data (ArrayList<DataItem>) and format
               // each element placed as defined in list_row.xml
               CustomAdapter adapter = new CustomAdapter(mContext, R.layout.list_row, data);
               myList.setAdapter(adapter);

               // When a myList item is clicked, show a Toast.
               myList.setOnItemClickListener(new AdapterView.OnItemClickListener()
               {
                    public void onItemClick(AdapterView<?> parentAdapter, View view, int position, long id)
                    {
                         // If Item 1 is clicked 3 times, open new Activity
                     if(id == 1)
                     {
                          i++;
                          if(i == 3)
                          {
                               Intent intent = new Intent(mContext, FactoryScreen.class);
                           i = 0;
                           startActivity(intent);    
                          }
                          else
                          {
                                   ...
                          }
                     }
                     else
                     {
                          ...
                     }
                     }
                 });
             return rootView; // onCreateView must return a View variable if displaying a UI.
         }
     }

FactoryScreen.java（Activity要打开，ListView不显示）

import java.util.ArrayList;

import com.example.baseappwithcalibration.R;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;

public class FactoryScreen extends Activity {

    private Context mContext;
    private ArrayList<DataItem> data = new ArrayList<DataItem>();
    ListView myList;

    @Override
    public void onCreate (Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_factory_screen);

        mContext = this; // Get the context of the Activity and therefore the fragment
        myList = new ListView (mContext); // Create a ListView

        // Create elements to be added to the list
        ...

        // Add elements to the list
        ...
    }

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        // Inflate the view
        View rootView = inflater.inflate(R.layout.fragment_factory_screen, container, false);

        // (?) Identify myList to be a list to be placed in rootView
        myList=(ListView)findViewById(android.R.id.list);
        // Create and set the customised adapter to take data (ArrayList<DataItem>) and format
        // each element as defined in list_row.xml
        CustomAdapter adapter = new CustomAdapter(mContext, R.layout.list_row, data);
        myList.setAdapter(adapter);

        // When a myList item is clicked, show a Toast.
        myList.setOnItemClickListener(new AdapterView.OnItemClickListener()
        {
            public void onItemClick(AdapterView<?> parentAdapter, View view, int position, long id)
            {
                // This is used in the form of Toast.makeText(Context, Text, Duration);
                Toast.makeText(FactoryScreen.this, "This is the description of the parameter.", Toast.LENGTH_SHORT).show();
            }
        });
        return rootView; // onCreateView must return a View variable if displaying a UI.
    }
}

fragment_factory_screen.xml（包含 FactoryScreen.xml 的布局）

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical" >

    <ListView 
        android:drawSelectorOnTop="false"
        android:id="@android:id/list"
        android:layout_height="0dip"
        android:layout_weight="1"
        android:layout_width="match_parent" >
    </ListView> 

</LinearLayout>

感谢任何帮助/指导！

Answer 1

没有为活动调用onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 的方法。因此在您的情况下不会执行该函数。这就是ListView 不可见的原因。因此，在 FactoryScreen Activity 中，将代码从该方法 onCreateView() 移动到 onCreate()。

@Override
public void onCreate (Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_factory_screen);

    mContext = this; // Get the context of the Activity and therefore the fragment

    // (?) Identify myList to be a list to be placed in rootView
    myList=(ListView)findViewById(android.R.id.list);

    // Create and set the customised adapter to take data (ArrayList<DataItem>) and format
    // each element as defined in list_row.xml
    CustomAdapter adapter = new CustomAdapter(mContext, R.layout.list_row, data);
    myList.setAdapter(adapter);

    // When a myList item is clicked, show a Toast.
    myList.setOnItemClickListener(new AdapterView.OnItemClickListener()
    {
        public void onItemClick(AdapterView<?> parentAdapter, View view, int position, long id)
        {
            // This is used in the form of Toast.makeText(Context, Text, Duration);
            Toast.makeText(FactoryScreen.this, "This is the description of the parameter.", Toast.LENGTH_SHORT).show();
        }
    });

}

}

Answer 2

在您的 FactoryScreen 中，在您的 onCreate 方法中

myList = new ListView (mContext); // Create a ListView

您没有在布局中添加 listView。

如果布局 R.layout.fragment_factory_screen 包含 ListView，你可以用它来检索它

myList=(ListView)findViewById(myId);

否则您必须使用代码添加到您的视图中。

Answer 3

试试这个

在onCreateView()

myList=(ListView)rootView.findViewById(android.R.id.list);