片段内 ListView 中的 SQLite 数据答案

【问题标题】：SQLite data in a ListView inside a Fragment片段内 ListView 中的 SQLite 数据
【发布时间】：2016-08-20 04:45:09
【问题描述】：

我已经创建了一半的应用程序，但我被困在需要从 SQLite 数据库检索数据并将它们显示在选项卡片段内的 ListView 中的位置。
我有两个选项卡，其中一个将显示 SQLite 数据库中的数据列表。

stackoverflow 上的一些人建议使用 RecyclerView 而不是 ListView，但我很难使用 ListView，而且我对 RecyclerView 一无所知。
我是 Android 新手，我觉得这些问题对于专业开发人员来说并不难，但对我来说却是相当具有挑战性的。

我可以在片段中显示数据库中的数据，但我只能显示最新条目的一行。
我想在 Fragment 中显示从最新到旧、从上到下的整个列表。

问题的另一部分是列表不会自动更新。
我需要关闭应用程序并重新打开它以查看 Fragment 中的最新条目。

这是我的代码 -

PeopleFragemnt.class 之前

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.example.kevin.sugar.DataBase.DateBaseHelper;
import com.example.kevin.sugar.DataBase.Information;
import com.example.kevin.sugar.R;

/**
 * A simple {@link Fragment} subclass.
 */
public class PeopleFragment extends Fragment {

    DateBaseHelper dateBaseHelper;
    SQLiteDatabase sqLiteDatabase;
    Cursor cursor;

    TextView name,weight,height;

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View mview = inflater.inflate(R.layout.person_row, container, false);

        name = (TextView)mview.findViewById(R.id.person_name);
        weight = (TextView)mview.findViewById(R.id.heatbeat);
        height = (TextView)mview.findViewById(R.id.bpm_upper_lower);

        dateBaseHelper = new DateBaseHelper(getContext());
        sqLiteDatabase = dateBaseHelper.getReadableDatabase();
        cursor = dateBaseHelper.getUserInformation();
        if (cursor.moveToFirst()){
            do{
                String user_name,user_weight,user_height;
                user_name = cursor.getString(cursor.getColumnIndex(Information.NAME));
                user_weight = cursor.getString(cursor.getColumnIndex(Information.WEIGHT));
                user_height = cursor.getString(cursor.getColumnIndex(Information.HEIGHT));

                Log.e("App",user_name+ "" + user_height + " " +user_weight);
                name.setText(user_name);
                weight.setText(user_weight);
                height.setText(user_height);

            }while (cursor.moveToNext());
        }

        return mview;
    }

}

编辑

PeopleFragement.class 的变化

import android.content.Context;


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.example.kevin.sugar.R;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Kuro on 4/20/2016.
 */
public class ListDataAdapter extends ArrayAdapter {

    List mlist = new ArrayList();

    public ListDataAdapter(Context context, int resource) {
        super(context, resource);
    }

    @Override
    public void add(Object object) {
        super.add(object);
        mlist.add(object);

    }

    static class LayoutHandler{
        TextView name, weight,height;
    }

    @Override
    public int getCount() {
        return mlist.size();
    }

    @Override
    public Object getItem(int position) {
        return mlist.get(position);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View mview = convertView;
        LayoutHandler layoutHandler;
        if(mview==null){
            LayoutInflater layoutInflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            mview = layoutInflater.inflate(R.layout.person_row,parent,false);
            layoutHandler = new LayoutHandler();
            layoutHandler.name = (TextView)mview.findViewById(R.id.person_name);
            layoutHandler.weight = (TextView)mview.findViewById(R.id.heatbeat);
            layoutHandler.height = (TextView)mview.findViewById(R.id.bpm_upper_lower);

            mview.setTag(layoutHandler);
        }else {
            layoutHandler = (LayoutHandler) mview.getTag();
        }
        DataProvider dataProvider = (DataProvider)this.getItem(position);
        layoutHandler.name.setText(dataProvider.getName());
        layoutHandler.weight.setText(dataProvider.getWeight());
        layoutHandler.height.setText(dataProvider.getHeight());
        return mview;
    }
}

ListDataAdapter.Class

import android.content.Context;


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.example.kevin.sugar.R;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Kuro on 4/20/2016.
 */
public class ListDataAdapter extends ArrayAdapter {

    List mlist = new ArrayList();

    public ListDataAdapter(Context context, int resource) {
        super(context, resource);
    }

    @Override
    public void add(Object object) {
        super.add(object);
        mlist.add(object);

    }

    static class LayoutHandler{
        TextView name, weight,height;
    }

    @Override
    public int getCount() {
        return mlist.size();
    }

    @Override
    public Object getItem(int position) {
        return mlist.get(position);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View mview = convertView;
        LayoutHandler layoutHandler;
        if(mview==null){
            LayoutInflater layoutInflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            mview = layoutInflater.inflate(R.layout.person_row,parent,false);
            layoutHandler = new LayoutHandler();
            layoutHandler.name = (TextView)mview.findViewById(R.id.person_name);
            layoutHandler.weight = (TextView)mview.findViewById(R.id.heatbeat);
            layoutHandler.height = (TextView)mview.findViewById(R.id.bpm_upper_lower);

            mview.setTag(layoutHandler);
        }else {
            layoutHandler = (LayoutHandler) mview.getTag();
        }
        DataProvider dataProvider = (DataProvider)this.getItem(position);
        layoutHandler.name.setText(dataProvider.getName());
        layoutHandler.weight.setText(dataProvider.getWeight());
        layoutHandler.height.setText(dataProvider.getHeight());
        return mview;
    }
}

DataProvide.class

public class DataProvider {

    private String name;
    private String weight;
    private String height;

    public DataProvider(String name,String weight,String height){
        this.name = name;
        this.weight = weight;
        this.height = height;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getWeight() {
        return weight;
    }

    public void setWeight(String weight) {
        this.weight = weight;
    }

    public String getHeight() {
        return height;
    }

    public void setHeight(String height) {
        this.height = height;
    }
}

错误日志

FATAL EXCEPTION: main
                                                                                Process: com.example.kevin.sugar, PID: 29352
                                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
                                                                                    at com.example.kevin.sugar.Fragments.PeopleFragment.onCreateView(PeopleFragment.java:40)
                                                                                    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
                                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
                                                                                    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
                                                                                    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
                                                                                    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
                                                                                    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:570)
                                                                                    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
                                                                                    at android.support.v4.view.ViewPager.populate(ViewPager.java:1106)
                                                                                    at android.support.v4.view.ViewPager.populate(ViewPager.java:952)
                                                                                    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1474)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5537)
                                                                                    at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:610)
                                                                                    at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:677)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5537)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                                                    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5537)
                                                                                    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                                                    at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
                                                                                    at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5537)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5537)
                                                                                    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
                                                                                    at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
                                                                                    at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5537)
                                                                                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
                                                                                    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2615)
                                                                                    at android.view.View.measure(View.java:17565)
                                                                                    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2045)
                                                                                    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1196)
                                                                                    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1409)
                                                                                    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1084)
                                                                                    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5990)
                                                                                    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
                                                                                    at android.view.Choreographer.doCallbacks(Choreographer.java:580)
                                                                                    at android.view.Choreographer.doFrame(Choreographer.java:550)
                                                                                    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
                                                                                    at android.os.Handler.handleCallback(Handler.java:739)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                    at android.os.Looper.loop(Looper.java:135)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:5343)
                                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                                    at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)

【问题讨论】：

您将获得 3 个 TextViews 行中的所有值。最后一个仍然存在，因为循环结束了。这不是使用 ListView 的方式：您必须填充一个 Adapter，然后将 Adapter 传递给 ListView。您应该在 custom rows in a ListView filled from a database in Android 上搜索教程。
感谢您的回复。你能解释一下适配器部分吗？我没听懂。
使用 Adapter 创建 ArrayList 然后完美运行。
请查看android.widget.SimpleCursorAdapter。如果您需要一些示例代码，请查看 SDK 中 legacy\ApiDemos\src\com\example\android\apis\view\List7.java 下的示例
@BobMalooga 我采纳了你的建议并创建了一个适配器。我从视频教程中创建了这个适配器，所以我认为我在为我的应用程序制作它时犯了一些错误。运行我的应用程序时崩溃并打印问题中提到的错误日志。我已经添加了所有代码。

标签： android sqlite listview android-fragments android-sqlite

【解决方案1】：

根据堆栈跟踪，JVM 找不到您的列表视图，因此我抛出空指针异常。这是您必须使用的代码 sn-p 才能在列表视图中显示数据。

PeopleFragment.java

public class PeopleFragment extends Fragment {

private DateBaseHelper dateBaseHelper;
private SQLiteDatabase sqLiteDatabase;
private List<DataProvider> mPersonList;
private ListDataAdapter mListDataAdapter;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View mview = inflater.inflate(R.layout.fragment_person, container, false);

    ListView listView = (ListView) mview.findViewById(R.id.lv_person);
    mPersonList = new ArrayList<>();
    dateBaseHelper = new DateBaseHelper(getContext());
    sqLiteDatabase = dateBaseHelper.getReadableDatabase();
    Cursor cursor = dateBaseHelper.getUserInformation();
    if (cursor.moveToFirst()){
        do{
            String user_name,user_weight,user_height;
            user_name = cursor.getString(cursor.getColumnIndex(Information.NAME));
            user_weight = cursor.getString(cursor.getColumnIndex(Information.WEIGHT));
            user_height = cursor.getString(cursor.getColumnIndex(Information.HEIGHT));
            DataProvider dataProvider = new DataProvider(user_name,user_weight,user_height);
            mPersonList.add(dataProvider);
        }while (cursor.moveToNext());
    }

    mListDataAdapter = new ListDataAdapter(getContext(),R.layout.row_person,mPersonList);
    listView.setAdapter(mListDataAdapter);
    return mview;
  }
}

fragment_person.xml

<?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/lv_person"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

</LinearLayout>

你的 DataProvider.java

public class DataProvider {

private String name;
private String weight;
private String height;

public DataProvider(String name,String weight,String height){
    this.name = name;
    this.weight = weight;
    this.height = height;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getWeight() {
    return weight;
}

public void setWeight(String weight) {
    this.weight = weight;
}

public String getHeight() {
    return height;
}

public void setHeight(String height) {
    this.height = height;
  }
}

ListDataAdapter.java

public class ListDataAdapter extends ArrayAdapter {

List<DataProvider> mlist;

public ListDataAdapter(Context context, int resource,List<DataProvider> list )
{
    super(context, resource);
    mlist = list;
}

static class LayoutHandler{
    TextView name, weight,height;
}

@Override
public int getCount() {
    return mlist.size();
}

@Override
public Object getItem(int position) {
    return mlist.get(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View mview = convertView;
    LayoutHandler layoutHandler;
    if(mview==null){
        LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mview = layoutInflater.inflate(R.layout.row_person,parent,false);
        layoutHandler = new LayoutHandler();
        layoutHandler.name = (TextView)mview.findViewById(R.id.tv_name);
        layoutHandler.weight = (TextView)mview.findViewById(R.id.tv_weight);
        layoutHandler.height = (TextView)mview.findViewById(R.id.tv_height);

        mview.setTag(layoutHandler);
    }else {
        layoutHandler = (LayoutHandler) mview.getTag();
    }
    DataProvider dataProvider = (DataProvider)this.getItem(position);
    layoutHandler.name.setText(dataProvider.getName());
    layoutHandler.weight.setText(dataProvider.getWeight());
    layoutHandler.height.setText(dataProvider.getHeight());
    return mview;
   }
}

row_person.xml

<?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"
>

<TextView
    android:id="@+id/tv_name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    />
<TextView
    android:id="@+id/tv_weight"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    />
<TextView
    android:id="@+id/tv_height"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    />
</LinearLayout>

要更新数据，您无需重新打开应用程序，只需通知您的适配器新的数据集。假设您的光标数据发生了变化，并且您在同一页面上。所以只需要从 personList 中清除旧数据并添加新数据。这是代码

public void updatePersonList(){
    mPersonList.clear();
    dateBaseHelper = new DateBaseHelper(getContext());
    sqLiteDatabase = dateBaseHelper.getReadableDatabase();
    cursor = dateBaseHelper.getUserInformation();
    if (cursor.moveToFirst()){
        do{
            String user_name,user_weight,user_height;
            user_name = cursor.getString(cursor.getColumnIndex(Information.NAME));
            user_weight = cursor.getString(cursor.getColumnIndex(Information.WEIGHT));
            user_height = cursor.getString(cursor.getColumnIndex(Information.HEIGHT));

          DataProvider dataProvider = new DataProvider(user_name,user_weight,user_height);
          mPersonList.add(dataProvider);
        }while (cursor.moveToNext());
    }
  mListDataAdapter.notifyDataSetChanged();
}

【讨论】：

是的，昨天我解决了这个问题。我已经回复了 bob Malooga。感谢您的回复:) 无论如何。我会将其标记为已回答。
你能告诉我在哪里调用 updatepersonList 方法吗？
每当您的数据发生更改并且您在同一页面上时，即 PersonFragment.java。举个例子，我在同一个片段上有一个对话框，它在数据库中添加了新的 Person 详细信息。现在在数据库中添加数据后，我们关闭我们的对话框，但添加的人不会反映在列表中。因此，一旦我们关闭了我们调用 updatePersonList() 方法的对话框，它将在旅途中显示新的人员详细信息。我希望我能让你明白。
知道了。因此，我一直在使用一个对话框，该对话框在点击操作栏 [工具栏] 中的图标后出现。完成输入后，我单击完成按钮将值添加到数据库中。我在主要活动中对这部分进行了编码。片段使用 viewPagerAdapter.addFragments(new PeopleFragment(), "PEOPLE"); 调用，对话框使用 onOptionsItemSelected() 方法调用。我在 PeopleFragment 中添加了 updatePersonList。现在，如何在 onOptionsItemSelected 方法下的 Mainactivity 中调用它？