我创建了一个使用Cards的循环视图适配器。 在每张卡片中，我想动态地将文本视图添加到该卡片内的线性布局中。
但是，我无法运行代码
这是RV适配器：
public class RVAdapter extends RecyclerView.Adapter<RVAdapter.EventViewHolder>{
Context context;
List<Events> events;
Calculations calculations = new Calculations();
RVAdapter(List<Events> events){
this.events = events;
}
@Override
public int getItemCount() {
return events.size();
}
@Override
public EventViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.card_view, viewGroup, false);
EventViewHolder pvh = new EventViewHolder(v);
return pvh;
}
@Override
public void onBindViewHolder(EventViewHolder eventViewHolder, int i) {
eventViewHolder.eventName.setText(events.get(i).getName());
eventViewHolder.eventLocation.setText(events.get(i).getLocationName());
eventViewHolder.eventDate.setText(calculations.UnixTimeConverter(events.get(i).getUnixTimeStamp())[0]);
eventViewHolder.eventTime.setText(calculations.UnixTimeConverter(events.get(i).getUnixTimeStamp())[1]);
//TODO(2):Change code to dynamically add textviews with the proper parameters to the LinearLayout;
//eventViewHolder.eventParticipants.setText(calculations.ParticipantConcatenation(events.get(i).getParticipants()));
for (String x: events.get(i).getParticipants()) {
TextView tv=new TextView(context);
LinearLayout.LayoutParams params=new LinearLayout.LayoutParams
(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
params.leftMargin=50;
params.topMargin=i*50;
tv.setText(x);
tv.setTextSize((float) 20);
tv.setPadding(20, 50, 20, 50);
tv.setLayoutParams(params);
eventViewHolder.eventParticipants.addView(tv) ;
}
}
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
}
public static class EventViewHolder extends RecyclerView.ViewHolder {
CardView cv;
TextView eventName;
TextView eventTime;
TextView eventLocation;
TextView eventDate;
//TODO(1):Change the type of eventParticipants to Linear Layout;
LinearLayout eventParticipants;
EventViewHolder(View itemView) {
super(itemView);
cv = itemView.findViewById(R.id.CardViewItem);
eventName = itemView.findViewById(R.id.event_name);
eventTime = itemView.findViewById(R.id.event_time);
eventDate = itemView.findViewById(R.id.event_date);
eventLocation = itemView.findViewById(R.id.event_location);
eventParticipants = itemView.findViewById(R.id.event_participants);
}
}
}
错误似乎出现在我实例化新TextView并传入Context的地方。 我试过传递一个＆＃34;这个＆＃34;进入它，但它导致构建时间错误说：
Textview中的TextView（android.context.Context）无法应用于（... RVAdapter）
我也试过传递
MainActivity.this
，但是这会导致构建时错误，说'＃34; MainActivity.this不是封闭类。＆＃34;
如果我只是传入上下文，则会导致运行时NullPointerException错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.view.ViewConfiguration.get(ViewConfiguration.java:359)
at android.view.View.<init>(View.java:3587)
at android.view.View.<init>(View.java:3682)
at android.widget.TextView.<init>(TextView.java:637)
at android.widget.TextView.<init>(TextView.java:632)
at android.widget.TextView.<init>(TextView.java:628)
at android.widget.TextView.<init>(TextView.java:624)
at com.example.android.gatheraround.RVAdapter.onBindViewHolder(RVAdapter.java:56)
at com.example.android.gatheraround.RVAdapter.onBindViewHolder(RVAdapter.java:24)
at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6400)
at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6433)
at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5377)
at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5640)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5482)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5478)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2215)
at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1542)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1502)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:595)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3625)
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3067)
at android.view.View.measure(View.java:17547)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1083)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:615)
at android.view.View.measure(View.java:17547)
at android.support.v4.widget.NestedScrollView.measureChildWithMargins(NestedScrollView.java:1417)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.support.v4.widget.NestedScrollView.onMeasure(NestedScrollView.java:482)
at android.view.View.measure(View.java:17547)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:713)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:785)
at android.view.View.measure(View.java:17547)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:17547)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
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:17547)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.view.View.measure(View.java:17547)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
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:17547)
at android.view.ViewGroup.measureChildWithMarg
08-15 19:27:17.358 3080-3080/com.example.android.gatheraround I/Process: Sending signal. PID: 3080 SIG: 9
以下是主要活动和布局的代码，如果它有帮助：
public class MainActivity extends AppCompatActivity {
Button eventListButton;
private BottomSheetBehavior mBottomsheetbehvior;
RecyclerView rv;
LinearLayoutManager llm;
Context context;
public List<Events> events;
@Override
protected void onCreate(Bundle savedInstanceState) {
events = new ArrayList<Events>();
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Find Button
eventListButton = (Button) findViewById(R.id.eventlistbutton);
//Find bottom sheet
android.support.v4.widget.NestedScrollView bottomsheet =
(android.support.v4.widget.NestedScrollView) findViewById(R.id.bottomsheet);
//Add bottomsheet behavior to view
mBottomsheetbehvior = BottomSheetBehavior.from(bottomsheet);
mBottomsheetbehvior.setHideable(true);
mBottomsheetbehvior.setPeekHeight(400);
mBottomsheetbehvior.setState(BottomSheetBehavior.STATE_HIDDEN);
eventListButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(mBottomsheetbehvior.getState() == BottomSheetBehavior.STATE_EXPANDED) {
mBottomsheetbehvior.setState(BottomSheetBehavior.STATE_COLLAPSED);
eventListButton.setText("Hide");
}
else if(mBottomsheetbehvior.getState() == BottomSheetBehavior.STATE_COLLAPSED) {
mBottomsheetbehvior.setState(BottomSheetBehavior.STATE_HIDDEN);
eventListButton.setText("Event List Button");
}
else if(mBottomsheetbehvior.getState() == BottomSheetBehavior.STATE_HIDDEN) {
mBottomsheetbehvior.setState(BottomSheetBehavior.STATE_EXPANDED);
eventListButton.setText("Peek");
}
}
});
//Bottomsheet callbacks
mBottomsheetbehvior.setBottomSheetCallback(new BottomSheetBehavior.BottomSheetCallback() {
@Override
public void onStateChanged(@NonNull View bottomSheet, int newState) {
if (newState == BottomSheetBehavior.STATE_EXPANDED) {
eventListButton.setText("Peek");
}
else if (newState == BottomSheetBehavior.STATE_COLLAPSED) {
eventListButton.setText("Hide");
}
else if (newState == BottomSheetBehavior.STATE_HIDDEN) {
eventListButton.setText("Event List Button");
}
}
@Override
public void onSlide(@NonNull View bottomSheet, float slideOffset) {
}
});
//Recyler View
rv = (RecyclerView) findViewById(R.id.rv);
rv.setHasFixedSize(true);
llm = new LinearLayoutManager(context);
String[] participants = {"Tamim","Chiharu","Azmain","Miyoshi"};
events.add(new Events(1302719286,"U22 project",participants,new LatLng(37.652832,219.839478),"Saizeriya"));
events.add(new Events(1502419296,"U22 project",participants,new LatLng(32.652832,19.839478),"Hiroo"));
events.add(new Events(1901719266,"U22 project",participants,new LatLng(19.652832,39.839478),"Canada"));
events.add(new Events(1204219286,"U22 project",participants,new LatLng(100.652832,13.839478),"Tokyo Monorail"));
RVAdapter adapter = new RVAdapter(events);
rv.setAdapter(adapter);
rv.setLayoutManager(new LinearLayoutManager(context));
}
}
主要活动
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/bgLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="0dp"
android:paddingLeft="0dp"
android:paddingRight="0dp"
android:paddingTop="0dp"
tools:context=".MainActivity">
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="8dp"
android:text="EventList Button"
android:id="@+id/eventlistbutton"
/>
</RelativeLayout>
</ScrollView>
<android.support.v4.widget.NestedScrollView
android:id="@+id/bottomsheet"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="true"
android:background="@color/recyclerview_background"
app:layout_behavior="@string/bottom_sheet_behavior"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:layout_height="match_parent"
android:layout_width="match_parent"
android:id="@+id/rv"
android:layout_marginLeft="@dimen/recyclerviewhorizontalpadding"
android:layout_marginRight="@dimen/recyclerviewhorizontalpadding"
>
</android.support.v7.widget.RecyclerView>
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>
和CardView：
<android.support.v7.widget.CardView
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/CardViewItem"
card_view:cardCornerRadius="@dimen/cardviewcorner"
card_view:cardElevation="8dp"
card_view:cardBackgroundColor="@color/cardbackground2"
android:layout_marginTop="16dp"
>
<LinearLayout
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="wrap_content"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="@color/cardbackground"
>
<TextView
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="2"
tools:text="Dick Museum Tour"
android:textSize="18sp"
android:padding="@dimen/cardmargin"
android:textStyle="bold"
android:textColor="@color/white"
android:id="@+id/event_name"
/>
<TextView
android:layout_height="match_parent"
android:layout_width="0dp"
android:layout_weight="1"
android:textSize="18dp"
android:padding="@dimen/cardmargin"
android:textStyle="bold"
android:textColor="@color/white"
tools:text="8/24"
android:textAlignment="viewEnd"
android:id="@+id/event_date"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="@dimen/card_view_height"
android:background="@color/cardbackground2"
android:orientation="vertical"
>
<TextView
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
tools:text="Time:"
android:textColor="@color/white"
android:textSize="18sp"
android:gravity="center_vertical"
android:paddingLeft="@dimen/cardmargin"
android:id="@+id/event_time"
/>
<TextView
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
tools:text="Location:"
android:textColor="@color/white"
android:textSize="18sp"
android:gravity="center_vertical"
android:paddingLeft="@dimen/cardmargin"
android:clickable="true"
android:id="@+id/event_location"
/>
<HorizontalScrollView
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
>
<!--TODO(3):Update the view as a Linear Layout-->
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/event_participants"
android:orientation="horizontal"
>
</LinearLayout>
</HorizontalScrollView>
</LinearLayout>
</LinearLayout>
</android.support.v7.widget.CardView>
请注意我已经尝试使用TextView而不是LinearLayout的代码版本，其中我将所有名称连接成一个完整的字符串，这非常合适。
我现在正在尝试为每个名称创建一个TextView，并将其添加到Linear Layout。
答案 0 :(得分：0)
试试这个：从活动传递上下文并在适配器构造函数中获取它
RVAdapter adapter = new RVAdapter(this,events); //add thia line in MainActivity.this
在适配器
中添加它
RVAdapter(Context context,List<Event> event){
this.context=context;
this.events = events;
}
答案 1 :(得分：0)
这是因为您从未在适配器中设置Context。 在适配器中添加构造函数并设置Context变量。
public class RVAdapter extends RecyclerView.Adapter<RVAdapter.EventViewHolder> {
Context context;
public RVAdapter(Context context,...){
this.context = context
}
}
RVAdapter adapter = new RVAdapter(this,events);
答案 2 :(得分：0)
将Context添加到RVAdapter构造函数中，如下所示：
RVAdapter(List<Events> events, Context context){
this.events = events;
this.events = events;
}
答案 3 :(得分：0)
像这样引用你的EventViewHolder：
public class EventViewHolder extends RecyclerView.ViewHolder {
CardView cv;
TextView eventName;
TextView eventTime;
TextView eventLocation;
TextView eventDate;
LinearLayout eventParticipants;
EventViewHolder(View itemView) {
super(itemView);
cv = (CardView) itemView.findViewById(R.id.CardViewItem);
eventName = (TextView) itemView.findViewById(R.id.event_name);
eventTime = (TextView) itemView.findViewById(R.id.event_time);
eventDate = (TextView) itemView.findViewById(R.id.event_date);
eventLocation = (TextView) itemView.findViewById(R.id.event_location);
eventParticipants = (LinearLayout) itemView.findViewById(R.id.event_participants);
}
}
使用以下方式从MainActivity类传递上下文：
RVAdapter adapter = new RVAdapter(events, this);
在RVAdapter课程内：
private Context context;
private List<Event> events;
RVAdapter(List<Event> events, Context context){
this.events = events;
this.context=context;
}