我正在尝试通过点击第一个活动的recyclelerView打开一个包含recyclelerView的活动。但现在，当我点击recyclerView应用程序时，崩溃时会显示以下消息。
10-18 09：30：49.912 13018-13018 / in.mumbaitravellers.mtleaders E / AndroidRuntime：致命例外：主要 过程：in.mumbaitravellers.mtleaders，PID：13018
java.lang.RuntimeException：无法启动活动 ComponentInfo {in.mumbaitravellers.mtleaders / in.mumbaitravellers.mtleaders.activity.DetailActivity}： java.lang.NullPointerException：尝试调用虚方法'void android.support.v7.widget.RecyclerView.setHasFixedSize（boolean）'上 null对象引用
在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2426） 在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2490） 在android.app.ActivityThread.-wrap11（ActivityThread.java）
在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1354）
在android.os.Handler.dispatchMessage（Handler.java:102）
在android.os.Looper.loop（Looper.java:148）
在android.app.ActivityThread.main（ActivityThread.java:5443）
at java.lang.reflect.Method.invoke（Native Method）
在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:728） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:618）
引起：java.lang.NullPointerException：尝试调用虚拟 方法'无效 android.support.v7.widget.RecyclerView.setHasFixedSize（boolean）'上 null对象引用
在 in.mumbaitravellers.mtleaders.activity.DetailActivity.setupRecycler（DetailActivity.java:120） 在 in.mumbaitravellers.mtleaders.activity.DetailActivity.onCreate（DetailActivity.java:52） 在android.app.Activity.performCreate（Activity.java:6245）
在 android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1130） 在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2379） 在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2490） 在android.app.ActivityThread.-wrap11（ActivityThread.java）
在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1354） 在android.os.Handler.dispatchMessage（Handler.java:102）
在android.os.Looper.loop（Looper.java:148）
在android.app.ActivityThread.main（ActivityThread.java:5443）
at java.lang.reflect.Method.invoke（Native Method）
在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:728） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:618） 10-18 09：31：13.376 1801-2412 /？ E / native：暂停false
java代码如下：
public class DetailActivity extends AppCompatActivity {
private ExpenseAdapter adapter;
private Realm realm;
private LayoutInflater inflater;
private FloatingActionButton fab;
private RecyclerView recycler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
fab = (FloatingActionButton) findViewById(R.id.fab);
recycler = (RecyclerView) findViewById(R.id.recycler);
//get realm instance
this.realm = RealmController.with(this).getRealm();
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
/*String event = getIntent().getStringExtra("eventName");
TextView tv = (TextView) findViewById(R.id.txt_EventName);
tv.setText(event);*/
setupRecycler();
if (!Prefs.with(this).getPreLoad()) {
setRealmData();
}
// refresh the realm instance
RealmController.with(this).refresh();
// get all persisted objects
// create the helper adapter and notify data set changes
// changes will be reflected automatically
setRealmAdapter(RealmController.with(this).getExpenses());
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
inflater = DetailActivity.this.getLayoutInflater();
View content = inflater.inflate(R.layout.activity_add_new_expense, null);
final EditText editExpense = (EditText) content.findViewById(R.id.edtxt_expense);
final EditText editDescription = (EditText) content.findViewById(R.id.edtxt_description);
AlertDialog.Builder builder = new AlertDialog.Builder(DetailActivity.this);
builder.setView(content)
.setTitle("Add Expense")
.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Expense expense = new Expense();
expense.setId((int) (RealmController.getInstance().getExpenses().size() + System.currentTimeMillis()));
expense.setAmount(editExpense.getText().toString());
expense.setDescription(editDescription.getText().toString());
realm.beginTransaction();
realm.copyToRealm(expense);
realm.commitTransaction();
adapter.notifyDataSetChanged();
// scroll the recycler view to bottom
recycler.scrollToPosition(RealmController.getInstance().getExpenses().size() - 1);
}
})
.setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
AlertDialog dialog = builder.create();
dialog.show();
}
});
}
public void setRealmAdapter(RealmResults<Expense> expenses) {
RealmExpenseAdapter realmExpenseAdapter = new RealmExpenseAdapter(this.getApplicationContext(), expenses, true);
adapter.setRealmAdapter(realmExpenseAdapter);
adapter.notifyDataSetChanged();
}
private void setupRecycler() {
// use this setting to improve performance if you know that changes
// in content do not change the layout size of the RecyclerView
recycler.setHasFixedSize(true);
// use a linear layout manager since the cards are vertically scrollable
final LinearLayoutManager layoutManager = new LinearLayoutManager(this);
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recycler.setLayoutManager(layoutManager);
// create an empty adapter and add it to the recycler view
adapter = new ExpenseAdapter(this);
recycler.setAdapter(adapter);
}
private void setRealmData() {
ArrayList<Expense> expenses = new ArrayList<>();
for (Expense e : expenses) {
// Persist your data easily
realm.beginTransaction();
realm.copyToRealm(e);
realm.commitTransaction();
}
Prefs.with(this).setPreLoad(true);
}
}
xml文件如下：
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="in.mumbaitravellers.mtleaders.activity.DetailActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_detail" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@drawable/ic_action_add" />
</android.support.design.widget.CoordinatorLayout>
Recycler View Code：
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/card_expense"
style="@style/AppTheme.Card.Margins"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/text_amount"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="@dimen/margin_small"
android:paddingBottom="@dimen/margin_normal"
android:paddingLeft="@dimen/margin_large"
android:paddingRight="@dimen/margin_large"
android:paddingTop="@dimen/margin_large"
android:textColor="#555555"
android:text="\u20B9"
android:textSize="40dp"
android:textStyle="bold" />
<TextView
android:layout_width="match_parent"
android:layout_height="25dp"
android:id="@+id/text_description"
android:textSize="20dp"/>
</LinearLayout>
</android.support.v7.widget.CardView>
Content Detail.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/recyclerExpense"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:showIn="@layout/activity_detail"
tools:context="in.mumbaitravellers.mtleaders.activity.DetailActivity"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />
代码有什么问题，请帮忙。 提前谢谢！
答案 0 :(得分：1)
您的问题在于对RecyclerView
更改您的代码：
recycler = (RecyclerView) findViewById(R.id.recycler);
到
recycler = (RecyclerView) findViewById(R.id.recyclerExpense);