将新数据添加到arrayList时出现奇怪的Array-adapter问题

时间：2018-08-04 17:32:08

标签： android arraylist getter-setter

我这里似乎有一个奇怪的问题。我有一个带有5个文本视图的自定义适配器的ArrayList。我能够第一次添加到此列表中就可以保存并保存甚至重新加载，但是在重新加载后，我的Adapter类在尝试向列表中添加另一个项目时在getter方法上抛出了空指针。我知道NUll指针，但是问题出在试图将另一个项目添加到列表中吗？我的适配器类仅适用于1个视图吗？我不知道为什么它为null或为什么一开始它不是null。这是堆栈跟踪

更新的堆栈跟踪

08-04 14:23:17.855 10000-10000/com.apklegion.cltoollog E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.apklegion.cltoollog, PID: 10000
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.ArrayList.get(int)' on a null object reference
    at com.apklegion.cltoollog.ToolListAdapter.getView(ToolListAdapter.java:34)
    at android.widget.AbsListView.obtainView(AbsListView.java:2346)
    at android.widget.ListView.measureHeightOfChildren(ListView.java:1281)
    at android.widget.ListView.onMeasure(ListView.java:1188)
    at android.view.View.measure(View.java:18805)
    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
    at android.view.View.measure(View.java:18805)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
    at android.view.View.measure(View.java:18805)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
    at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:400)
    at android.view.View.measure(View.java:18805)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.view.View.measure(View.java:18805)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
    at android.view.View.measure(View.java:18805)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
    at android.view.View.measure(View.java:18805)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
    at android.view.Choreographer.doCallbacks(Choreographer.java:670)
    at android.view.Choreographer.doFrame(Choreographer.java:606)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5417)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

，这里是指出错误的适配器类。 更新以反映当前错误

public class ToolListAdapter extends ArrayAdapter<Toolinfo> {

 private Context mcontext;
int mResource;

public ToolListAdapter(Context context, int resource, ArrayList<Toolinfo> 
objects) {
    super(context, resource, objects);
    mcontext = context;
    mResource = resource;
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull 
ViewGroup parent) {

  -error is here>    String part_number = 
 objects.get(position).getPart_number();
    String serial_number = objects.get(position).getSerial_number();
    int employee_number = objects.get(position)).getEmployee_nummber();
    String date_out = objects.get(position).getOut_time();
    String date_in = objects.get(position).getIn_time();

    Toolinfo toolinfo = new Toolinfo(part_number,serial_number,employee_number,date_out,date_in);
    LayoutInflater layoutInflater = LayoutInflater.from(mcontext);
    convertView = layoutInflater.inflate(mResource,parent,false);

    TextView parnum = (TextView)convertView.findViewById(R.id.patnum);
    TextView sernum = (TextView)convertView.findViewById(R.id.sernum);
    TextView empnum = (TextView)convertView.findViewById(R.id.empnum);
    TextView timeout = (TextView)convertView.findViewById(R.id.timeout);
    TextView timein = (TextView)convertView.findViewById(R.id.timein);

    parnum.setText(part_number);
    sernum.setText(serial_number);
    empnum.setText(String.valueOf(employee_number));
    timeout.setText((date_out));
    timein.setText((date_in));
    return convertView;

}
}

这是吸气剂和吸气剂

public class Toolinfo {

private String part_number;
private String serial_number;
private int employee_nummber;
private String out_time;
private String in_time;


public Toolinfo(String part_number, String serial_number, int employee_nummber, String out_time, String in_time){
    this.part_number = part_number;
    this.serial_number = serial_number;
    this.employee_nummber = employee_nummber;
    this.out_time = out_time;
    this.in_time = in_time;



}

public String getPart_number() {
    return part_number;
}

public void setPart_number(String part_number) {
    this.part_number = part_number;
}

public String getSerial_number() {
    return serial_number;
}

public void setSerial_number(String serial_number) {
    this.serial_number = serial_number;
}

public int getEmployee_nummber() {
    return employee_nummber;
}

public void setEmployee_nummber(int employee_nummber) {
    this.employee_nummber = employee_nummber;
}

public String getOut_time() {
    return out_time;
}

public void setOut_time(String out_time) {
    this.out_time = out_time;
}

public String getIn_time() {
    return in_time;
}

public void setIn_time(String in_time) {
    this.in_time = in_time;
}

}   最后但并非最不重要的是存放ArrayList的主要活动类的相关位

public class MainActivity extends AppCompatActivity {

List<String> list = new ArrayList<>();
ArrayAdapter<String> adapter;
ListView listView;
Button button;
static  final int ADD_TOOL = 1;
CustomAdapter customAdapter;
public static final String PREFS_NAME = "MyPreferencesFile";
final String[] tools = {"30-200 Torque Wrench","Calipers","Push Pull Gague"};
String date_out,date_in;
String part_number,serial_number;
int employee_number;
Context context;
ArrayList<Toolinfo> toolinfos;
String currentDateandTime;
DatabaseHelper db;
Toolinfo tool1;

public static String TAG =“ Main”; 

ToolListAdapter myadapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    toolinfos = new ArrayList<>();
    myadapter = new ToolListAdapter(this,R.layout.logrowlayout,toolinfos );





    loadData();


    button = findViewById(R.id.button);
    listView =  findViewById(R.id.listview);
    listView.setAdapter(myadapter);

    Intent getData = getIntent();
    if(getData.hasExtra("part number")&& getData.hasExtra("serial number") && getData.hasExtra("employee number")) {
        final String part_number = getData.getStringExtra("part number");
        showToast("has extras");

        String serial_number = getData.getStringExtra("serial number");
         showToast(serial_number);
        int employee_number = getData.getIntExtra("employee number", 0);
        // showToast(String.valueOf(employee_number));
        //addItems(part_number, serial_number, employee_number);

        SimpleDateFormat sdf = new SimpleDateFormat("ddMMyyyy_HHmmss");
        String currentDateandTime = sdf.format(new Date());
        populateData(part_number,serial_number,employee_number,date_out,"out");

     }else {
    showToast("info not present");


}



    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            addTool();
        }
    });



}



public void populateData(String part_number,String serial_number,int employee_number, String date_out, String date_in) {
    //loadData();
    SimpleDateFormat sdf = new SimpleDateFormat("MMdd");
    String currentDateandTime = sdf.format(new Date());
    Toolinfo tool = new Toolinfo(part_number, serial_number, employee_number, currentDateandTime, "out");
    myadapter.add(tool);
    myadapter.notifyDataSetChanged();
    saveData(tool);

        for (int i = 0;  i < toolinfos.size(); i++) {
            Log.d(TAG, "populateData: " + toolinfos.get(i));


           //toolinfos.add(tool1);

        }

}

private  void saveData(Toolinfo tool1) {
    SharedPreferences preferences = getSharedPreferences("Shared prefs", MODE_PRIVATE);
    SharedPreferences.Editor editor = preferences.edit();
    Gson gson = new Gson();
    String json = gson.toJson(tool1);
    editor.putString("toolobj",json);
    showToast(json);
    editor.commit();



    //Log.i("tag",json.toString());
    editor.apply();
    showToast("Data Saved");

}
private void loadData(){
    SharedPreferences preferences = getSharedPreferences("Shared prefs", MODE_PRIVATE);
    Gson gson = new Gson();
    String json = preferences.getString("toolobj","");

    if (json == null){
        showToast("no data");

    }else {
        Toolinfo tool1 = gson.fromJson(json, Toolinfo.class);
        toolinfos.add(tool1);


    }




}
private void addTool(){

    Intent i = new Intent(MainActivity.this,Toolsignout.class);
    startActivity(i);
    saveData(tool1);



}
public void showToast(String msg){
    Toast.makeText(this,msg,Toast.LENGTH_LONG).show();
}

@Override
protected void onResume() {
  //  loadData();
    super.onResume();
}

}

2 个答案:

答案 0 :(得分：0)

在您的ToolsListAdapter中为ArrayList<Toolinfo> objects;添加类变量，并分配与上下文相似的变量。

然后在您的getView()方法中，将getItem(position)更改为objects.get(position)。

答案 1 :(得分：-1)

您只保存一个对象并在SharedPreferences中加载一个对象。

private  void saveData(Toolinfo tool1) {
    SharedPreferences preferences = getSharedPreferences("Shared prefs", MODE_PRIVATE);
    SharedPreferences.Editor editor = preferences.edit();
    Gson gson = new Gson();
    String json = gson.toJson(tool1);
    editor.putString("toolobj",json);
    showToast(json);
    editor.commit();

    editor.apply();
    showToast("Data Saved");

}
private void loadData(){
    SharedPreferences preferences = getSharedPreferences("Shared prefs", MODE_PRIVATE);
    Gson gson = new Gson();
    String json = preferences.getString("toolobj","");

    if (json == null){
        showToast("no data");
    }else {
        Toolinfo tool1 = gson.fromJson(json, Toolinfo.class);
        toolinfos.add(tool1);
    }
}

在您的load方法上，json永远不会等于null。如果首选项没有得到一个对象，它将返回一个空字符串。因此，将始终转到else块。现在，如果json不是有效的json或无法反序列化为Toolinfo对象，则gson.fromJson将不会引发任何异常。相反，它将仅返回null。因此，您要将null添加到列表中。

此外，请记住：
共享首选项是键值对。如果要保存项目列表或记录，则可能需要查看数据库。

TL; DR
您的代码结构仅保存一个值，您可以尝试将列表保存为共享首选项。将加载方法上的if语句从检查json字符串是否为null更改为empy。并且，在将对象添加到列表之前，请检查该对象是否为空。

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