Question

我试图在recyclerView中显示数据，但是我的应用程序崩溃了

公共类Search_book_admin扩展了AppCompatActivity {

ArrayList<Model_class> modelClassArrayList;
myAdapert myadapter;
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    recyclerView = (RecyclerView) findViewById(R.id.rv);
    setContentView(R.layout.activity_search_book_admin);
    modelClassArrayList = new ArrayList<>();
    AddItems();
    myadapter = new myAdapert(modelClassArrayList);

    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    recyclerView.setAdapter(myadapter);
}
private  void AddItems()
{
    try {
        for(int i=0;i<20;i++)
        {
            modelClassArrayList.add(new Model_class(R.drawable.ic_action_name,
                    "name: "+i,
                    "email"+i));
        }
    }
    catch (Exception e)
    {
        Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
    }
}

@Override
public void onBackPressed() {
    finish();
}

（（我的适配器类））

公共类myAdapert扩展了RecyclerView.Adapter { ArrayList modelClassArrayList;

public myAdapert(ArrayList<Model_class> modelClassArrayList) {
    this.modelClassArrayList = modelClassArrayList;
}

@NonNull
@Override
public myViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    View customView = LayoutInflater.from(viewGroup.getContext())
            .inflate(R.layout.custom_row,viewGroup,false);
    myViewHolder myviewHolder = new myViewHolder(customView);
    return myviewHolder;
}

@Override
public void onBindViewHolder(@NonNull myViewHolder myViewHolder, int i) {
    Model_class model_class = modelClassArrayList.get(i);
    myViewHolder.contactPic.setImageResource(model_class.getImage());
    myViewHolder.contactName.setText(model_class.getName());
    myViewHolder.contectEmail.setText(model_class.getEmail());

}

@Override
public int getItemCount() {
    return modelClassArrayList.size();
}

public class myViewHolder extends RecyclerView.ViewHolder {
    ImageView contactPic;
    TextView contactName,contectEmail;
    public myViewHolder(@NonNull View itemView) {
        super(itemView);
        contactPic = itemView.findViewById(R.id.image);
        contactName = itemView.findViewById(R.id.name);
        contectEmail = itemView.findViewById(R.id.email);
    }
}

2019-06-15 17：39：16.114 6337-6337 /？ E / ProActivieLaunch：发送广播 2019-06-15 17：39：16.121 4466-4702 /？ E / ActivityManager：接收到TouchDown意图，启动ActiveLaunch 2019-06-15 17：39：16.139 29048-29048 /？ E /合子：isWhitelistProcess-进程被列入白名单 2019-06-15 17：39：16.140 29048-29048 /？ E /合子：accessInfo：1 2019-06-15 17：39：16.563 4010-4053 /？ E / BufferQueueProducer：[com.sec.android.app.launcher / com.sec.android.app.launcher.activities.LauncherActivity [6337]＃0]断开连接：未连接（req = 1） 2019-06-15 17：39：16.566 4466-6303 /？ E / WindowManager：win = Window {cdfa8e6 u0 com.sec.android.app.launcher / com.sec.android.app.launcher.activities.LauncherActivity} destroySurfaces：appStopped = false win.mWindowRemovalAllowed = false win.mRemoveOnExit = false win .mViewVisibility = 8调用者= com.android.server.wm.WindowManagerService.tryStartExitingAnimation：2748 com.android.server.wm.WindowManagerService.relayoutWindow：2446 com.android.server.wm.Session.relayoutForTranslate：287 android.view.IWindowSession $ Stub.onTransact：432 com.android.server.wm.Session.onTransact：186 android.os.Binder.execTransact：739 2019-06-15 17：39：17.376 4466-4537 /？ E / WindowManager：win = Window {7d266dd u0启动画面com.example.library_management_system EXITING} destroySurfaces：appStopped = false win.mWindowRemovalAllowed = true win.mRemoveOnExit = true win.mViewVisibility = 0 caller = com.android.server.wm.AppWindowToken .destroySurfaces：870 com.android.server.wm.AppWindowToken.destroySurfaces：851 com.android.server.wm.WindowState.onExitAnimationDone：5423 com.android.server.wm.WindowStateAnimator.onAnimation完成：319 com.android.server.wm .WindowState.onAnimationFinished：5845 com.android.server.wm .- $$ Lambda $ yVRF8YoeNdTa8GR1wDStVsHu8xM.run：2 com.android.server.wm.SurfaceAnimator.lambda $ getFinishedCallback $ 0：100 2019-06-15 17：39：19.682 29048-29048 / com.example.library_management_system E / AndroidRuntime：FATAL EXCEPTION：main 流程：com.example.library_management_system，PID：29048 java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.library_management_system / com.example.library_management_system.Search_book_admin}：java.lang.NullPointerException：尝试调用虚拟方法'void android.support.v7.widget.RecyclerView。 setHasFixedSize（boolean）'在空对象引用上在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3115）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3258）在android.app.servertransaction.LaunchActivityItem.execute（LaunchActivityItem.java:78）在android.app.servertransaction.TransactionExecutor.executeCallbacks（TransactionExecutor.java:108）在android.app.servertransaction.TransactionExecutor.execute（TransactionExecutor.java:68）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1955）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:214）在android.app.ActivityThread.main（ActivityThread.java:7058）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:493）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:965）原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.support.v7.widget.RecyclerView.setHasFixedSize（boolean）' 在com.example.library_management_system.Search_book_admin.onCreate（Search_book_admin.java:25）在android.app.Activity.performCreate（Activity.java:7327）在android.app.Activity.performCreate（Activity.java:7318）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1275）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3095）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3258）在android.app.servertransaction.LaunchActivityItem.execute（LaunchActivityItem.java:78）在android.app.servertransaction.TransactionExecutor.executeCallbacks（TransactionExecutor.java:108）在android.app.servertransaction.TransactionExecutor.execute（TransactionExecutor.java:68）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1955）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:214）在android.app.ActivityThread.main（ActivityThread.java:7058）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:493）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:965） 2019-06-15 17：39：19.769 29101-29101 /？ E / Zygote：isWhitelistProcess-进程被列入白名单

Answer 1

将此代码粘贴到onCreate方法中

setContentView(R.layout.activity_search_book_admin);
recyclerView = (RecyclerView) findViewById(R.id.rv);
modelClassArrayList = new ArrayList<>();
AddItems();
myadapter = new myAdapert(modelClassArrayList);

recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

recyclerView.setAdapter(myadapter);

recyclerView的运行时异常

1 个答案: