我通过各种教程使用RecyclerView制作应用程序。现在应用程序崩溃了。这是我的MainActivity：
import android.os.*;
import android.support.design.widget.*;
import android.support.v4.view.*;
import android.support.v7.app.*;
import android.support.v7.widget.*;
import android.util.*;
import android.view.*;
import java.util.*;
public class MainActivity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;
private static String LOG_TAG = "CardViewActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar myToolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(myToolbar);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.addTab(tabLayout.newTab().setText("Planes"));
tabLayout.addTab(tabLayout.newTab().setText("Solids"));
tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
final ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
final PagerAdapter adapter = new ViewPagerAdapter
(getSupportFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(adapter);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
mRecyclerView.setHasFixedSize(true);
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
mAdapter = new MyRecyclerViewAdapter(getDataSet());
mRecyclerView.setAdapter(mAdapter);
// Code to Add an item with default animation
//((MyRecyclerViewAdapter) mAdapter).addItem(obj, index);
// Code to remove an item with default animation
//((MyRecyclerViewAdapter) mAdapter).deleteItem(index);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.toolbar_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onResume() {
super.onResume();
((MyRecyclerViewAdapter) mAdapter).setOnItemClickListener(new MyRecyclerViewAdapter
.MyClickListener() {
@Override
public void onItemClick(int position, View v) {
Log.i(LOG_TAG, " Clicked on Item " + position);
}
});
}
private ArrayList<PlanesData> getDataSet() {
ArrayList results = new ArrayList<PlanesData>();
for (int index = 0; index < 20; index++) {
PlanesData obj = new PlanesData("Some Primary Text " + index,
"Secondary " + index);
results.add(index, obj);
}
return results;
}
}
这是logcat的一部分，错误：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.im.shapes, PID: 2979
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.im.shapes/com.im.shapes.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
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:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at com.im.shapes.MainActivity.onCreate(MainActivity.java:54)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
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:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
所以我用它做了什么＆＃34; setHasFixedSize（boolean）＆＃34;？ 如果您需要更多资源（布局，活动），请在评论中告诉我。
修改
activity_main.xml中：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:id="@+id/my_recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical"/>
</RelativeLayout>
看来id是正确的......
谢谢
答案 0 :(得分：0)
id my_recycler_view可能不正确，您可以与我们分享activity_main.xml
答案 1 :(得分：0)
所以，我错过了我的布局不在setContentView中。就这样。无论如何，谢谢你的帮助。