我正在开发Android应用程序，并将使用Realm（这是我的第一个应用程序与Realm）。但是我的recyclerviewadapter有问题。
我得到致命的异常
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.udacity.stockhawk, PID: 9880
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.udacity.stockhawk/com.udacity.stockhawk.ui.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'io.realm.RealmList com.udacity.stockhawk.data.Parent.getStockList()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2521)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2595)
at android.app.ActivityThread.access$800(ActivityThread.java:178)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
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:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'io.realm.RealmList com.udacity.stockhawk.data.Parent.getStockList()' on a null object reference
at com.udacity.stockhawk.ui.MainActivity.onCreate(MainActivity.java:66)
at android.app.Activity.performCreate(Activity.java:6092)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1112)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2468)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2595)
at android.app.ActivityThread.access$800(ActivityThread.java:178)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5631)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
我的适配器是：
class StockAdapter extends RealmRecyclerViewAdapter<Stock, StockAdapter.StockViewHolder> {
private final Context context;
private final DecimalFormat dollarFormatWithPlus;
private final DecimalFormat dollarFormat;
private final DecimalFormat percentageFormat;
private final StockAdapterOnClickHandler clickHandler;
StockAdapter(Context context, StockAdapterOnClickHandler clickHandler,
OrderedRealmCollection<Stock> data) {
super(context, data, true);
this.context = context;
this.clickHandler = clickHandler;
dollarFormat = (DecimalFormat) NumberFormat.getCurrencyInstance(Locale.US);
dollarFormatWithPlus = (DecimalFormat) NumberFormat.getCurrencyInstance(Locale.US);
dollarFormatWithPlus.setPositivePrefix("+$");
percentageFormat = (DecimalFormat) NumberFormat.getPercentInstance(Locale.getDefault());
percentageFormat.setMaximumFractionDigits(2);
percentageFormat.setMinimumFractionDigits(2);
percentageFormat.setPositivePrefix("+");
}
@Override
public StockViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View item = LayoutInflater.from(context).inflate(R.layout.list_item_quote, parent, false);
return new StockViewHolder(item);
}
@Override
public void onBindViewHolder(StockViewHolder holder, int position) {
final Stock stock = getItem(position);
holder.symbol.setText(stock.getDataset_code());
double currentPrice = stock.getQuoteHistory().first().getValue();
double oldPrice = stock.getQuoteHistory().get(1).getValue();
holder.price.setText(dollarFormat.format(currentPrice));
double rawAbsoluteChange = currentPrice - oldPrice;
double percentageChange = (rawAbsoluteChange/oldPrice) * 100.0;
if (rawAbsoluteChange > 0) {
holder.change.setBackgroundResource(R.drawable.percent_change_pill_green);
} else {
holder.change.setBackgroundResource(R.drawable.percent_change_pill_red);
}
String change = dollarFormatWithPlus.format(rawAbsoluteChange);
String percentage = percentageFormat.format(percentageChange / 100);
if (Utils.getDisplayMode(context)
.equals(context.getString(R.string.pref_display_mode_absolute_key))) {
holder.change.setText(change);
} else {
holder.change.setText(percentage);
}
}
interface StockAdapterOnClickHandler {
void onClick(String symbol);
}
class StockViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
@BindView(R.id.symbol)
TextView symbol;
@BindView(R.id.price)
TextView price;
@BindView(R.id.change)
TextView change;
StockViewHolder(View itemView) {
super(itemView);
ButterKnife.bind(this, itemView);
itemView.setOnClickListener(this);
}
@Override
public void onClick(View v) {
int adapterPosition = getAdapterPosition();
clickHandler.onClick(getItem(adapterPosition).getDataset_code());
}
}
}
我对创建代码的活动是：
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
realm = Realm.getDefaultInstance();
adapter = new StockAdapter(this, this, realm.where(Parent.class).findFirst().getStockList());
stockRecyclerView.setAdapter(adapter);
stockRecyclerView.setLayoutManager(new LinearLayoutManager(this));
swipeRefreshLayout.setOnRefreshListener(this);
swipeRefreshLayout.setRefreshing(true);
onRefresh();
QuoteSyncJob.initialize(this);
new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.RIGHT) {
@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
return false;
}
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
String symbol = adapter.getItem(viewHolder.getAdapterPosition()).getDataset_code();
Utils.removeStock(realm, symbol);
}
}).attachToRecyclerView(stockRecyclerView);
}
我需要做些什么来解决这个问题？ 项目中的其他课程正在运作。 我使用此https://github.com/realm/realm-android-adapters作为示例
P.S。：这是关于Udacity Nanodegree的项目3。
答案 0 :(得分：0)
您是否对您的Realm对象进行了任何更改？如果您添加，删除或修改了任何内容（例如归档类型或名称），则必须清除整个数据库并再次创建所有对象。
您可以使用以下方式执行此操作：
Realm.deleteAll()