Question

我创建了一半的应用程序而且我遇到了需要从SQLite数据库中检索数据并将其显示在Tab片段内的ListView中的情况。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的新手，我觉得这些问题对于专业开发人员来说并不困难，但对我来说这是非常具有挑战性的。

我可以在片段中显示数据库中的数据，但是我只能显示一行是最新的条目。
我想在片段中显示从最新到旧，从上到下的整个列表。

问题的另一部分是列表没有自动更新我需要关闭应用程序并重新打开它以查看片段中的最新条目。

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;
    }

}

修改

更改PeopleFragement.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;
    }
}

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;
    }
}

错误记录

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)

Answer 1

根据堆栈跟踪，JVM找不到listview，因此我抛出了nullpointer异常。以下是您必须使用的代码段才能在listview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>

您的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>

更新您不需要重新打开应用程序的数据只需要使用新的数据集通知您的适配器。假设您的光标数据已更改并且您位于同一页面上。所以只需要清除personList中的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();
}

片段内的ListView中的SQLite数据

1 个答案: