[英]Android - Adapter NullPointerException
如果这是重复的事,我事先表示歉意。 我仍然是Android开发的新手,并尝试寻找一种解决方案,但是找不到可行的解决方案。
我正在创建一个待办事项应用程序,并在适配器中收到此错误。
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String assignment.Model.getAssignment()' on a null object reference
at assignment.Adapter.getView(Adapter.java:39)
它所引用的代码行是
assignment.setText(modelItems[position].getAssignment());
我相信我将其设置为错误的原因是什么导致该错误,但是我不确定如何解决。
这是我其余代码的一部分,以供参考:
MainActivity.Java-onActivityResult
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
String assignmentSentBack = data.getStringExtra("editAssignment");
Integer monthSentBack = data.getIntExtra("month", 0);
Integer daySentBack = data.getIntExtra("day", 0);
modelItems = new Model[100];
ArrayList<Model> modelArrayList = new ArrayList<>(Arrays.asList(modelItems));
modelArrayList.add(new Model(assignmentSentBack, (monthSentBack + 1) + "/" + daySentBack, 0));
lv = (ListView) findViewById(R.id.listAssignment);
ListAdapter adapter = new Adapter(this, modelItems);
lv.setAdapter(adapter);
}
第二活动-onSendActivity(按钮)
public void onSendAssignment (View view) {
EditText editAssignmentET = (EditText)
findViewById(R.id.editAssignment);
String editAssignment = String.valueOf(editAssignmentET.getText());
DatePicker datePickerDP = (DatePicker)
findViewById (R.id.datePicker);
Integer month = Integer.valueOf(datePickerDP.getMonth());
Integer day = Integer.valueOf(datePickerDP.getDayOfMonth());
Intent goingBack = new Intent();
goingBack.putExtra("editAssignment", editAssignment);
goingBack.putExtra ("month", month);
goingBack.putExtra("day", day);
setResult(RESULT_OK, goingBack);
finish();
}
适配器
public class Adapter extends ArrayAdapter {
Model[] modelItems = null;
Context context;
public Adapter(Context context, Model[] resource) {
super(context, R.layout.row, resource);
this.context = context;
this.modelItems = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = ((Activity) context).getLayoutInflater();
convertView = inflater.inflate(R.layout.row, parent, false);
TextView assignment = (TextView) convertView.findViewById(R.id.assignment);
TextView dueDate = (TextView) convertView.findViewById(R.id.dueDate);
CheckBox cb = (CheckBox) convertView.findViewById(R.id.checkBox);
assignment.setText(modelItems[position].getAssignment());
dueDate.setText(modelItems[position].getDueDate());
if (modelItems[position].getValue() == 1)
cb.setChecked(true);
else
cb.setChecked(false);
return convertView;
}
}
模型
public class Model {
String assignment;
String dueDate;
int value;
Model (String assignment, String dueDate, int value){
this.assignment = assignment;
this.dueDate = dueDate;
this.value = value;
}
public String getAssignment(){
return this.assignment;
}
public String getDueDate(){
return this.dueDate;
}
public int getValue(){
return this.value;
}
}
任何帮助表示赞赏。 谢谢。
您应该尝试将其包装在内部Holder类中并在该类中定义参数
public class Adapter extends ArrayAdapter {
Model[] modelItems = null;
Context context;
public Adapter(Context context, Model[] resource) {
super(context, R.layout.row, resource);
this.context = context;
this.modelItems = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = ((Activity) context).getLayoutInflater();
if (convertView == null) {
holder = new ViewHolder();
convertView = vi.inflate(R.layout.list_layout, null);
// Find the child views.
holder.assignment= (TextView) convertView.findViewById(R.id.txt_name);
holder.dueDate= (Button) convertView.findViewById(R.id.btn_invite);
holder.cb= (Button) convertView.findViewById(R.id.btn_track);
convertView.setTag(holder);
//....
}
// Reuse existing row view
else {
holder = (ViewHolder)convertView.getTag();
}
return convertView;
}
class ViewHolder {
TextView assignment;
TextView dueDate;
CheckBox cb;
}
}
更改
public class Adapter extends ArrayAdapter {
至
public class Adapter extends ArrayAdapter<Model> {
您在此处创建了大小为100的模型数组:
modelItems = new Model[100];
因此,正在创建100个模型,但是所有100个索引的null
。
然后,您使用该数组创建了ArrayList
:
ArrayList<Model> modelArrayList = new ArrayList<>(Arrays.asList(modelItems));
因此,您的modelArrayList
具有100个null
对象。 您在哪里使用哪个BTW。
您正在将modelItems
传递到Adapter
构造函数中。 因此,由于所有项目均为null
,因此您将获得此异常。
尝试做这样的事情:
ArrayList<Model> modelArrayList = new ArrayList<>();
modelArrayList.add(new Model(assignmentSentBack, (monthSentBack + 1) + "/" + daySentBack, 0));
类似地,添加更多这样的模型对象。 在适配器的构造函数中传递此modelArrayList
,并使用它(而不是数组)显示列表。
lv = (ListView) findViewById(R.id.listAssignment);
ListAdapter adapter = new Adapter(this, modelArrayList)
因此,您的适配器将如下所示:
ArrayList<Model> modelArrayList;
Context context;
public Adapter(Context context, ArrayList<Model> resource) {
super(context, R.layout.row, resource);
this.context = context;
this.modelArrayList = resource;
}
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