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我正在做一个项目，我必须显示一个系的可用教授列表。我不想显示所有教授，而是让学生按部门搜索教授。结果，学生将登录，根据姓名、部门、​​课程 ID 或全部搜索教授。我正在使用自定义列表适配器。我注意到适配器对象不为空，但列表仍显示“没有可显示的记录。我认为问题与我在 Prof.Detail 类中设置适配器的方式有关。我在这里做错了什么？请参阅下面的代码：

教授类包com.mb.professor；

    import android.os.Bundle;
    import android.support.v4.app.FragmentActivity;
    import android.support.v4.app.FragmentManager;
    import android.support.v4.app.FragmentTransaction;
    import android.view.View;
    import android.widget.AdapterView;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.Spinner;

    import com.mb.professor.asynctasks.ProfessorAsyncTask;

    /**
     * Created by Gagouche on 7/25/13.
     */
    public class Professors extends FragmentActivity {
       private Button bSearch;
        private EditText etSearchBy;
        private EditText etCourseId;
        private Spinner spSearchDecision;
        private String searchValue = null;
        private Professor[] _professor = null;
        public Professors()
        {

        }
        public Professors(Professor[] professor)
        {
            this._professor = professor;
        }
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.professor);
            InitialVariables();
        }

        private void InitialVariables()
        {
            bSearch = (Button) this.findViewById(R.id.bSearch);
            etSearchBy = (EditText) this.findViewById(R.id.etSearchByDepartment);
            etCourseId = (EditText) this.findViewById(R.id.etSearchByCouseId);
            spSearchDecision = (Spinner) this.findViewById(R.id.spOption);
            bSearch.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                  if(searchValue == "Department")
                    {

                        ProfessorAsyncTask professor = new ProfessorAsyncTask();
                        professor.execute("");

                        FragmentManager mFragment = getSupportFragmentManager();
                        FragmentTransaction ft = mFragment.beginTransaction();
                        ProfessorDetail pDetail = new ProfessorDetail();
                        pDetail.setProfessorAdapter(_professor);
                        ft.replace(R.id.fprofessorDetail, pDetail);
                        ft.addToBackStack(null);
                        ft.commit();
                    }
                }
            });

            spSearchDecision.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                @Override
                public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                     switch (position)
                     {
                         case 0:
                             searchValue = "By All";
                             break;
                         case 1:
                             searchValue = "Department";
                             break;
                         case 2:
                             searchValue = "CourseId";
                             break;
                     }
                }

                @Override
                public void onNothingSelected(AdapterView<?> parent) {
                    searchValue = "By All";
                }
            });
        }
    }

教授详细课

  package com.mb.professor;

import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;

import com.mb.professor.adapter.*;

/**
 * Created by Gagouche on 7/25/13.
 */
public class ProfessorDetail extends ListFragment {
   private  ProfessorAdapter adapter = null;
    Professor[] prof = null;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    public void setProfessorAdapter(Professor[] professor)
    {
        prof = professor;
    }
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        String [] emptyAdapter = {};
        if(prof == null)
        {
           ArrayAdapter<String> emptyListAdapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,emptyAdapter);
           setListAdapter(emptyListAdapter);
        } else
        {
            adapter = new ProfessorAdapter(getActivity(), R.layout.professor_row, prof);
            adapter.notifyDataSetChanged();
            setListAdapter(adapter);
        }

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.customizelayout, container, false);
    }
}

课程详情类

    package com.mb.professor;

    import android.os.Bundle;
    import android.support.v4.app.ListFragment;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;

    import com.mb.professor.adapter.CourseAdapter;

    import java.util.List;

    /**
     * Created by Gagouche on 7/25/13.
     */
    public class CourseDetail extends ListFragment {
       private CourseAdapter adapter = null;
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
        }

        public void setCourseData(Course[] course)
        {
          adapter = new CourseAdapter(getActivity(), R.layout.course_row, course);
        }
        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            String[] course = {};
            if(adapter == null)
            {
                ArrayAdapter<String> emptyAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1 , course );
                setListAdapter(adapter);
            } else
            {
                setListAdapter(adapter);
            }
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
         //   super.onCreateView(inflater, container, savedInstanceState);
            return inflater.inflate(R.layout.customizelayout, container, false);
        }
    }

登录课程

    package com.mb.professor;

    import android.content.Intent;
    import android.os.Bundle;
    import android.app.Activity;
    import android.view.Menu;
    import android.view.View;
    import android.widget.Button;
    import android.widget.EditText;

    public class Login extends Activity implements View.OnClickListener {
        Button btnLogin;
        EditText etUsername, etPassword;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.login);
            initializeVariables();
        }

        private void initializeVariables()
        {
           btnLogin = (Button) this.findViewById(R.id.btnLogin);
           etUsername = (EditText) this.findViewById(R.id.etUserName);
           etPassword = (EditText) this.findViewById(R.id.etPassword);
            btnLogin.setOnClickListener(this);
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.login, menu);
            return true;
        }

        @Override
        public void onClick(View v) {
            String uName = etUsername.getText().toString();
            String pWord = etPassword.getText().toString();
            if(uName.equals("college") && pWord.equals("florida"))
            {
               Intent intent = new Intent(this, Professors.class);
                startActivity(intent);
            }
        }
    }

AsyncTask 教授

       package com.mb.professor.asynctasks;

import android.os.AsyncTask;
import android.support.v4.app.FragmentActivity;

import com.mb.professor.Course;
import com.mb.professor.Professor;
import com.mb.professor.ProfessorDetail;
import com.mb.professor.Professors;
import com.mb.professor.R;

/**
 * Created by Gagouche on 8/1/13.
 */
public class ProfessorAsyncTask extends AsyncTask<String,Void,Professor[]> {
   private FragmentActivity fActivity;
    public ProfessorAsyncTask()
    {

    }
    @Override
    protected Professor[] doInBackground(String... params) {
        Professor[] professor = new Professor[5];
        professor[0] = new Professor("Finance", "John", "123", "Accounting");
        professor[1] = new Professor("Accounting", "Cain", "124", "finance");
        professor[2] = new Professor("Database", "Eugene", "125", "Music");
        professor[3] = new Professor("Finance", "Seikei", "126", "Engineer");
        professor[4] = new Professor("Finance", "Bojok", "127", "Math");

        return professor;
    }

    @Override
    protected void onPostExecute(Professor[] professors) {
        super.onPostExecute(professors);
       // ProfessorDetail professorDetailFragment = (ProfessorDetail)fActivity.getSupportFragmentManager().findFragmentById(R.id.fprofessorDetail);
     //   Professors prof = new Professors(professors);
    }
}

课程异步任务

    package com.mb.professor.asynctasks;

    import android.app.FragmentTransaction;
    import android.os.AsyncTask;
    import android.support.v4.app.FragmentActivity;

    import com.mb.professor.Course;
    import com.mb.professor.CourseDetail;
    import com.mb.professor.R;

    import java.util.List;

    /**
     * Created by Gagouche on 8/1/13.
     */
    public class CourseAsyncTask extends AsyncTask<String, Void, Course[]> {
    private FragmentActivity mActivity;
       private Course[] course = null;

        public CourseAsyncTask(FragmentActivity activity)
        {
            this.mActivity = activity;
        }
        @Override
        protected Course[] doInBackground(String... params) {
            Course[] course = new Course[5];
            course[0] = new Course("Finance", "John", "123");
            course[1] = new Course("Accounting", "Cain", "124");
            course[2] = new Course("Database", "Eugene", "125");
            course[3] = new Course("Finance", "Seikei", "126");
            course[4] = new Course("Finance", "Bojok", "127");

            return course;
        }

        @Override
        protected void onPostExecute(Course[] courses) {
            super.onPostExecute(courses);
            CourseDetail courseDetailFragment = (CourseDetail) mActivity.getSupportFragmentManager().findFragmentById(R.id.fCourseDetail);
            courseDetailFragment.setCourseData(courses);
        }
    }

适配器教授

    package com.mb.professor.adapter;

    import android.app.Activity;
    import android.content.Context;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.TextView;

    import com.mb.professor.*;

    import java.util.List;

    /**
     * Created by Gagouche on 8/1/13.
     */
    public class ProfessorAdapter extends ArrayAdapter<Professor> {
        private Context context;
        private int layoutResourceId;
        private Professor[] data = null;
        public ProfessorAdapter(Context context, int layoutResourceId, Professor[] data) {
            super(context, layoutResourceId, data);
            this.context = context;
            this.layoutResourceId = layoutResourceId;
            this.data = data;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View row = convertView;
            ProfessorHolder holder = null;
            if(row == null)
            {
                LayoutInflater inflater = ((Activity)context).getLayoutInflater();
                row = inflater.inflate(layoutResourceId,parent, false);
                holder = new ProfessorHolder();
                holder.tvFirstName = (TextView) row.findViewById(R.id.tvFirstName);
                holder.tvLastName = (TextView) row.findViewById(R.id.tvLastName);
                holder.tvCourse = (TextView) row.findViewById(R.id.tvCourseID);
                holder.tvDepartment = (TextView) row.findViewById(R.id.tvDepartment);
                row.setTag(holder);
            } else
            {
                holder = (ProfessorHolder) row.getTag();
            }

            Professor item = data[position];
            holder.tvFirstName.setText(item.getFirstName());
            holder.tvLastName.setText(item.getLastName());
            holder.tvDepartment.setText(item.getDepartmentID());
            holder.tvCourse.setText(item.getCourseId());
            return row;
        }

        static class ProfessorHolder
        {
          TextView tvFirstName;
          TextView tvLastName;
          TextView tvDepartment;
          TextView tvCourse;
        }
    }

课程适配器

    package com.mb.professor.adapter;

    import android.app.Activity;
    import android.content.Context;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.TextView;

    import com.mb.professor.Course;
    import com.mb.professor.R;

    /**
     * Created by Gagouche on 8/1/13.
     */
    public class CourseAdapter extends ArrayAdapter<Course> {
        private Context context;
        private int layoutResourceId;
        private Course[] data = null;
        public CourseAdapter(Context context, int resource, Course[] data) {
            super(context, resource, data);
            this.context = context;
            this.layoutResourceId = resource;
            this.data = data;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View row = convertView;
            CourseHolder holder = null;
            if(row == null)
            {
                LayoutInflater inflater = ((Activity)context).getLayoutInflater();
                row = inflater.inflate(layoutResourceId, parent, false);
                holder = new CourseHolder();
                holder.tvCourseInstructor = (TextView) row.findViewById(R.id.tvCourseInstructor);
                holder.tvCourseId = (TextView) row.findViewById(R.id.tvCourse);
                holder.tvCourseName = (TextView) row.findViewById(R.id.tvCourseName);
                row.setTag(holder);
            } else {
                holder = (CourseHolder) row.getTag();
            }

            Course item = data[position];
            holder.tvCourseId.setText(item.getCourseId());
            holder.tvCourseName.setText(item.getCourseName());
            holder.tvCourseInstructor.setText(item.getInstructorName());
            return row;
        }

        static class CourseHolder
        {
            TextView tvCourseName;
            TextView tvCourseInstructor;
            TextView tvCourseId;
        }
    }

登录 XML 

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="User Name"
                android:id="@+id/textView"
                android:layout_alignParentTop="true"
                android:layout_marginTop="30dp"
                android:layout_gravity="center_horizontal"
                android:layout_centerHorizontal="true"
                android:textSize="30sp"
                />

        <EditText
                android:layout_width="200sp"
                android:layout_height="wrap_content"
                android:id="@+id/etUserName"
                android:layout_below="@+id/textView"
                android:layout_centerHorizontal="true"
                android:layout_gravity="center_horizontal"
                android:layout_marginTop="10dp"/>

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Password"
                android:id="@+id/textView2"
                android:layout_below="@+id/editText"
                android:layout_centerHorizontal="true"
                android:layout_gravity="center_horizontal"
                android:layout_marginTop="10dp"
                android:textSize="30sp"
                />

        <EditText
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:inputType="textPassword"
                android:ems="10"
                android:id="@+id/etPassword"
                android:layout_below="@+id/textView2"
                android:layout_centerHorizontal="true"
                android:layout_gravity="center_horizontal"
                android:layout_marginTop="10dp"
                />

        <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Login"
                android:id="@+id/btnLogin"
                android:layout_gravity="center_horizontal"
                android:layout_centerVertical="true"
                android:layout_centerHorizontal="true"/>
    </LinearLayout>

XML教授

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


        <LinearLayout
                android:layout_width="0dp"
                android:layout_height="fill_parent"
                android:orientation="vertical"
                android:layout_weight="1"
                >
            <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Search For Professor"
                    android:id="@+id/textView"
                    android:layout_marginTop="10dp"
                    android:layout_marginLeft="10dp"
                    android:textSize="30sp"
                    />
            <EditText
                    android:layout_width="250dp"
                    android:layout_height="wrap_content"
                    android:hint="search by Department"
                    android:id="@+id/etSearchByDepartment"
                    android:layout_marginLeft="10dp"
                    android:layout_marginTop="5dp"
                    />

            <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Search by Course ID"
                    android:id="@+id/textView2"
                    android:layout_marginTop="10dp"
                    android:layout_marginLeft="10dp"
                    android:textSize="30sp"
                    />

            <EditText
                    android:layout_width="250dp"
                    android:layout_height="wrap_content"
                    android:id="@+id/etSearchByCouseId"
                    android:layout_marginLeft="10dp"
                    android:layout_marginTop="5dp"
                    />

            <Spinner
                    android:layout_width="321dp"
                    android:layout_height="wrap_content"
                    android:id="@+id/spOption"
                    android:entries="@array/searchOption"
                    android:layout_marginLeft="10dp"
                    android:layout_marginTop="5dp"

                    />
            <Button
                    android:id="@+id/bSearch"
                    android:text="Search"
                    android:layout_height="wrap_content"
                    android:layout_width="wrap_content"
                    android:layout_marginTop="10dp"
                    android:layout_marginLeft="5dp"
                    />

        </LinearLayout>

        <LinearLayout
                android:layout_width="0dp"
                android:layout_height="fill_parent"
                android:layout_weight="2"
                android:orientation="vertical"
                >

            <fragment
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:name="com.mb.professor.ProfessorDetail"
                    android:id="@+id/fprofessorDetail"
                    android:layout_weight="1"
                    android:layout_gravity="center"/>

            <fragment
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:layout_weight="2"
                    android:name="com.mb.professor.CourseDetail"
                    android:id="@+id/fCourseDetail"
                    android:layout_gravity="center"/>


        </LinearLayout>
    </LinearLayout>

教授行自定义 XML

    <?xml version="1.0" encoding="utf-8"?>

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                  android:orientation="horizontal"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent">

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="First Name"
                android:layout_marginLeft="10dp"
                android:id="@id/tvFirstName"
                android:layout_gravity="center_horizontal|top"/>

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Last Name"
                android:layout_marginLeft="10dp"
                android:id="@id/tvFirstName"
                android:layout_gravity="center_horizontal|top"/>

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="New Text"
                android:layout_marginLeft="10dp"
                android:id="@id/tvDepartment"
                android:layout_gravity="center_horizontal|top"/>

        <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="10dp"
                android:text="New Text"
                android:id="@id/tvCourseID"
                android:layout_gravity="center_horizontal|top"/>
    </LinearLayout>

自定义列表视图的布局

    <?xml version="1.0" encoding="utf-8"?>

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                  android:orientation="vertical"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent">
        <ListView
                android:id="@id/android:list"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="left|center_vertical"/>
        <TextView
                android:id="@id/android:empty"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="No Record to be displayed."
                android:textSize="25sp"
                android:layout_gravity="left|center_vertical"/>


    </LinearLayout>

这是一个例外：

08-05 13:26:25.619 716-731/com.android.exchange D/ExchangeService：从电子邮件应用程序收到 deviceId：空 08-05 13:26:25.619 716-731/com.android.exchange D/ExchangeService：！ ！！deviceId 未知；停止自我并重试 08-05 13:26:27.242 1055-1055/com.mb.professor D/AndroidRuntime: 关闭 VM 08-05 13:26:27.242 1055-1055/com.mb.professor W/dalvikvm: threadid =1：线程以未捕获的异常退出（组=0x40a71930）08-05 13:26:27.302 1055-1055/com.mb.professor E/AndroidRuntime：致命异常：主要 java.lang.NullPointerException：存储 == java 处的 null .util.Arrays$ArrayList.(Arrays.java:38) at java.util.Arrays.asList(Arrays.java:154) at android.widget.ArrayAdapter.(ArrayAdapter.java:128) at com.mb.professor。 com.mb 上的 adapter.ProfessorAdapter.(ProfessorAdapter.java:23)。

4

1 回答 1

1

我误会了吗？但是您notifyDataSetChange在 asynctask 完成之前调用。你必须调用你notifyDataSetChange的onPostExecute异步任务。因此，您的列表是空的。

在您的代码中，您在教授详细信息类中执行

adapter = new ProfessorAdapter(getActivity(), R.layout.professor_row, prof);
adapter.notifyDataSetChanged();
setListAdapter(adapter);

您通知数据更改并将适配器链接到列表。但你再也不会这样做了。您的 onPost Execute 为空。

您要做的就是将 移至adapter.notifyDataSetChanged();onPostExecute ，您的列表将被刷新。

编辑

让我向您展示我的代码示例。

public class MyAsyncTaskFragment extends Fragment {
    private ListView lv;
    private CustomAdapter adapter;
    private ArrayList<...your custom type here...> listItems = new ArrayList<...your custom type here...>(); 

    ...

    @Override
    public void onActivityCreated (Bundle savedInstanceState){ 
        //get the listView
        lv = (ListView) getView().findViewById(R.id.my_listview_name); 

        //create new adapter
        adapter = new CustomAdapter();

        //link adapter to listview
        lv.setAdapter(adapter);

        //in my case I want the async task to start over when the activity is created
        new DoAsyncTask().execute(); 
    }

    private class DoAsyncTask extends AsyncTask<Void, Integer, Integer>{
        protected void onPreExecute() {                                        
            listItems.clear(); 
        }

        protected Integer doInBackground(Void...voids) {
            //add items to the list                
            listItems.add(...your custom type here ...);
            return null;
        }

        protected void onPostExecute(Integer result) {
            if (listItems.size() > 0){ 
                adapter.notifyDataSetChanged(); 
            }
        }

    }    
}
于 2013-08-05T14:29:33.713 回答