首先，我很抱歉，因为我不确定如何正确呈现信息。我一直在尝试在 Activity 的“.onCreate()”方法中将项目加载到 ArrayList 中。堆栈跟踪的第一行内容如下:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.weslange.Term_Scheduling/com.weslange.Term_Scheduling.Term_ChangingDetails_Activity}: java.lang.UnsupportedOperationException
导致崩溃的行如下所示:
courseData_List.add( courseData_entry )
我之前曾通过访问 SQLite 数据库将项目加载到 RecyclerView 中取得成功。我目前的尝试包括使用 ArrayList 的“.add()”方法，但我显然做错了。我可以使用一些见解。
感谢您的宝贵时间。
Term_ChangingDetails_Activity.java:
public class Term_ChangingDetails_Activity extends AppCompatActivity
implements Term_ChangingDetails_RecyclerView_Adapter.ItemClickListener{
private Button saveButton;
int termID;
EditText termName_EditText;
Button startingDate_Button;
Button endingDate_Button;
Button courseSelection_Button;
Bundle dataArgument_Bundle_Example;
DialogFragment startingDateFragment;
DialogFragment endingDateFragment;
TermData termData_TransferInfo;
Database_Handling databaseHandling;
List< CourseData > courseData_List = Collections.emptyList();
RecyclerView recyclerView;
Term_ChangingDetails_RecyclerView_Adapter adapter;
@Override
protected void onCreate( Bundle savedInstanceState ) {
super.onCreate( savedInstanceState );
//The below line is necessary for showing info at all.
setContentView( R.layout.activity_term_changingdetails );
databaseHandling = new Database_Handling( this );
//&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
Intent intent = getIntent();
final TermData termData_Values = intent.getParcelableExtra( "termData_Parcelable" );
termID = termData_Values.getTermID();
//&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
//This displays a back button on the ToolBar at the top of the Activity.
getSupportActionBar().setDisplayHomeAsUpEnabled( true );
//This just changes the title of the ToolBar.
getSupportActionBar().setTitle( "Changing Details of This Term" );
//*****************************************************************
termName_EditText = findViewById( R.id.termNameXML );
termName_EditText.setText( termData_Values.getTermName() );
startingDate_Button = findViewById( R.id.startingDateButtonXML );
startingDate_Button.setText( termData_Values.getStartingDate() );
endingDate_Button = findViewById( R.id.endingDateButtonXML );
endingDate_Button.setText( termData_Values.getEndingDate() );
//*****************************************************************
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
saveButton = findViewById( R.id.saveButtonXML );
saveButton.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick( View view ) {
termData_TransferInfo = new TermData( termID,
termName_EditText.getText().toString(),
startingDate_Button.getText().toString(),
endingDate_Button.getText().toString() );
databaseHandling.updateTermData( termData_TransferInfo );
//TODO THERE IS ALSO THE NEED TO UPLOAD JSON DATA FOR THE COURSES AS A STRING TO THE SQLITE DATABASE.
//TODO 'courseData_List' IS WHERE TO PULL THE DATA FROM THROUGH GSON.
finish();
}
});
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
courseSelection_Button = findViewById( R.id.courseSelection_ButtonXML );
courseSelection_Button.setOnClickListener( new View.OnClickListener() {
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@Override
public void onClick( View view ) {
Intent intent = new Intent( Term_ChangingDetails_Activity.this, Term_CourseSelection_Activity.class );
CourseData_List_Container courseData_List_Container2 = new CourseData_List_Container( courseData_List );
intent.putExtra( "course_list_held", courseData_List_Container2 );
//This code refers to course selection.
startActivityForResult( intent, 1 );
}
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
});
recyclerView = findViewById( R.id.term_changingdetails_recyclerView_Array_in_XML );
LinearLayoutManager linearLayoutManager = new LinearLayoutManager( this );
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(
recyclerView.getContext(), linearLayoutManager.getOrientation() );
recyclerView.addItemDecoration( dividerItemDecoration );
recyclerView.setLayoutManager( linearLayoutManager );
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
//==========================================================================================
//TODO THERE IS THE NEED TO POPULATE 'courseData_List' FROM SQLITE THROUGH A JSON STRING.
//Testing purposes.
if ( databaseHandling.getCourseDataCount() > 0 ) {
int testInt = databaseHandling.getCourseData( 1 ).getCourseID().intValue();
Log.v( "SUCCESS??? ", "TESTING TESTING TESTING courseID: " + testInt );
System.out.println( "TESTING TESTING TESTING courseID: " + testInt );
}
if ( databaseHandling.getCourseDataCount() > 0 ) {
CourseData courseData_entry = databaseHandling.getCourseData( 1 );
//THE BELOW LINE CAUSES A CRASH.
courseData_List.add( courseData_entry );
}
//==========================================================================================
adapter = new Term_ChangingDetails_RecyclerView_Adapter( this, courseData_List );
recyclerView.setAdapter( adapter );
}
public void reveal_StartingDate_DatePicker( View v ) {
startingDateFragment = new DatePickerFragment_TERM_StartingDate();
startingDateFragment.setArguments( dataArgument_Bundle_Example );
startingDateFragment.show( getFragmentManager(), "starting date picker" );
}
public void setStartingDate_in_StartingDate_Button( String startingDate_for_Button ) {
startingDate_Button.setText( startingDate_for_Button );
}
public void reveal_EndingDate_DatePicker( View view ) {
endingDateFragment = new DatePickerFragment_TERM_EndingDate();
endingDateFragment.setArguments( dataArgument_Bundle_Example );
endingDateFragment.show( getFragmentManager(), "ending date picker" );
}
public void setEndingDate_in_EndingDate_Button( String endingDate_for_Button ) {
endingDate_Button.setText( endingDate_for_Button );
}
@Override
protected void onActivityResult( int requestCode, int resultCode, Intent data ) {
//This code refers to course selection.
if ( requestCode == 1 ) {
//==========================================================================================
if( resultCode == Activity.RESULT_OK ){
CourseData_List_Container test_CourseData_Container = data.getParcelableExtra( "course_list_chosen" );
courseData_List = test_CourseData_Container.getCourseData_List();
if ( courseData_List.isEmpty() == false ){
StringBuilder stringBuilder_Courses_in_List = new StringBuilder();
for ( CourseData courseData_Test : courseData_List ) {
stringBuilder_Courses_in_List.append( courseData_Test.getCourseID() + " " );
}
String result = "The following courseID numbers are in 'courseData_List': " + stringBuilder_Courses_in_List;
Toast.makeText( Term_ChangingDetails_Activity.this, result, Toast.LENGTH_LONG ).show();
}
else {
String result = data.getStringExtra( "result" );
Toast.makeText( Term_ChangingDetails_Activity.this, result, Toast.LENGTH_LONG ).show();
}
}
//==========================================================================================
if ( resultCode == Activity.RESULT_CANCELED ) {
Toast.makeText( Term_ChangingDetails_Activity.this, "No courses added or removed.",
Toast.LENGTH_LONG ).show();
}
}
}
//This is possibly for a future revision.
@Override
public void onItemClick( View view, int position ) {
}
@Override
public void onResume() {
super.onResume();
//**************************************************************************
adapter = new Term_ChangingDetails_RecyclerView_Adapter( this, courseData_List );
adapter.setClickListener( this );
recyclerView.setAdapter( adapter );
//**************************************************************************
adapter.notifyDataSetChanged();
}
}
最佳答案
Collections.emptyList()返回一个不可变的
不能在其中添加元素的列表。
使用这个
List< CourseData > courseData_List = new ArrayList<>();
代替这个
List< CourseData > courseData_List = Collections.emptyList();
有关更多信息，请阅读此 Collections.emptyList() vs. new instance
关于java.lang.RuntimeException : Unable to start activity ComponentInfo. ..(以错误的方式访问列表)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49269534/