android– 没有附加适配器;单击后退按钮并再次启动应用程序时跳过布局

概述AndroidStudio3.2Canary18kotlin_version=1.2.50我有一个使用recyclerview和适配器的简单应用程序.应用程序启动时会加载所有数据.但是,当我单击后退按钮并再次启动应用程序时.它不会显示数据(空白).如果我从内存中清除应用程序并启动应用程序.数据将正常加载.我从sqli @H_301_0@

AndroID Studio 3.2 Canary 18kotlin_version = 1.2.50

@H_301_0@我有一个使用recyclervIEw和适配器的简单应用程序.应用程序启动时会加载所有数据.
但是,当我单击后退按钮并再次启动应用程序时.它不会显示数据(空白).
如果我从内存中清除应用程序并启动应用程序.数据将正常加载.

@H_301_0@我从sqlite加载数据,每次都加载数据.因为它填充了insectDataModelList.

@H_301_0@进入RecyclerVIEw.java源代码后,原因是mAdapter为null.但是,我有
我将它设置为recyclervIEw时检查适配器是否正确.

@H_301_0@

voID dispatchLayout() {        if (mAdapter == null) {            Log.e(TAG, "No adapter attached; skipPing layout");            // leave the state in START            return;        }        ...}

@H_301_0@我的MainActivity.java是Java

@H_301_0@

public class MainActivity extends AppCompatActivity {    private RecyclerVIEw rvInsects;    @OverrIDe    protected voID onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentVIEw(R.layout.activity_main);        Toolbar toolbar = (Toolbar) findVIEwByID(R.ID.toolbar);        setSupportActionbar(toolbar);        rvInsects = (RecyclerVIEw)findVIEwByID(R.ID.recycler_vIEw);        DatabaseManager databaseManager = DatabaseManager.getInstance(this);        databaseManager.queryAllinsects("frIEndlyname");    }    private voID setupAdapter(List<InsectDataModel> insectDataModelList) {        final LayoutManager layoutManager = new linearlayoutmanager(                this, linearlayoutmanager.VERTICAL, false);        rvInsects.setLayoutManager(layoutManager);        rvInsects.setHasFixedSize(true);        final InsectAdapter insectAdapter = new InsectAdapter(insectDataModelList);        rvInsects.setAdapter(insectAdapter);        insectAdapter.notifyDataSetChanged();    }    /* Callback from database */    public voID loadAllinsects(final Cursor cursor) {        InsectInteractorMapper insectInteractorMapper = new InsectInteractorMapperImp();        final List<InsectDataModel> insectDataModelList = insectInteractorMapper.map(cursor);        /* data loaded with 24 items */        setupAdapter(insectDataModelList);    }}

@H_301_0@InsectAdapter.kt是Kotlin.

@H_301_0@

class InsectAdapter(private val insectList: MutableList<InsectDataModel>)    : RecyclerVIEw.Adapter<InsectAdapter.CustomInsectHolder>() {    overrIDe fun onCreateVIEwHolder(parent: VIEwGroup, vIEwType: Int): CustomInsectHolder {        val vIEw = LayoutInflater.from(parent.context)                .inflate(R.layout.insect_row_item, parent, false)        return CustomInsectHolder(vIEw)    }    overrIDe fun onBindVIEwHolder(holder: CustomInsectHolder, position: Int) {        holder.tvFrIEndlyname.text = insectList[position].frIEndlyname        holder.tvScIEntificname.text = insectList[position].scIEntificname    }    overrIDe fun getItemCount(): Int {        return insectList.size    }    class CustomInsectHolder(itemVIEw: VIEw) : RecyclerVIEw.VIEwHolder(itemVIEw) {        val ivDangerLevel: DangerLevelVIEw = itemVIEw.findVIEwByID(R.ID.ivDangerLevel)        val tvFrIEndlyname: TextVIEw = itemVIEw.findVIEwByID(R.ID.tvFrIEndlyname)        val tvScIEntificname: TextVIEw = itemVIEw.findVIEwByID(R.ID.tvScIEntificname)    }}

@H_301_0@数据库我使用rxjava2来进行查询

@H_301_0@

public class DatabaseManager {    private static DatabaseManager sInstance;    private MainActivity mainActivity;    private BUGsDbHelper mBUGsDbHelper;    public static synchronized DatabaseManager getInstance(MainActivity context) {        if (sInstance == null) {            sInstance = new DatabaseManager(context);        }        return sInstance;    }    private DatabaseManager(MainActivity context) {        mBUGsDbHelper = new BUGsDbHelper(context);        mainActivity = context;    }    @Suppresslint("CheckResult")    public voID queryAllinsects(String sortOrder) {        final InsectStorageInteractorImp insectStorageInteractorImp                = new InsectStorageInteractorImp(new InsectStorageImp(mBUGsDbHelper.getReadableDatabase()));        insectStorageInteractorImp.getAllSortedInsects(sortOrder)                .subscribeOn(Schedulers.io())                .observeOn(AndroIDSchedulers.mainThread())                .subscribe(new SingleObserver<Cursor>() {                    disposable disposable;                    @OverrIDe                    public voID onSubscribe(disposable d) {                        disposable = d;                    }                    @OverrIDe                    public voID onSuccess(Cursor cursor) {                        mainActivity.loadAllinsects(cursor);                        disposable.dispose();                    }                    @OverrIDe                    public voID one rror(Throwable e) {                        disposable.dispose();                    }                });    }}

@H_301_0@当应用程序第一次安装时,一切都按预期工作.如果你把它清除掉了.
但是,只有当您单击后退按钮,然后尝试启动应用程序时,它才会加载任何数据
因为在RecyclerVIEw类中mAdapter为null.

@H_301_0@当我单击后退按钮然后再次启动应用程序时.我得到的只是一个空白屏幕,即

@H_301_0@

@H_301_0@更新了DatabaseManager类,该类删除了单例并使用了弱引用来确保MainActivity实例被垃圾回收.

@H_301_0@

public class DatabaseManager {    private WeakReference<MainActivity> mainActivity;    private BUGsDbHelper mBUGsDbHelper;    public DatabaseManager(MainActivity context) {        mBUGsDbHelper = new BUGsDbHelper(context);        mainActivity = new WeakReference<>(context);    }    @Suppresslint("CheckResult")    public voID queryAllinsects(String sortOrder) {        final InsectStorageInteractorImp insectStorageInteractorImp                = new InsectStorageInteractorImp(new InsectStorageImp(mBUGsDbHelper.getReadableDatabase()));        insectStorageInteractorImp.getAllSortedInsects(sortOrder)                .subscribeOn(Schedulers.io())                .observeOn(AndroIDSchedulers.mainThread())                .subscribe(new SingleObserver<Cursor>() {                    disposable disposable;                    @OverrIDe                    public voID onSubscribe(disposable d) {                        disposable = d;                    }                    @OverrIDe                    public voID onSuccess(Cursor cursor) {                        mainActivity.loadAllinsects(cursor);                        disposable.dispose();                    }                    @OverrIDe                    public voID one rror(Throwable e) {                        disposable.dispose();                    }                });    }}

@H_301_0@非常感谢任何建议,

解决方法:

@H_301_0@单击后退按钮并重新启动应用程序时,将启动一个新的MainActivity实例.

@H_301_0@同时,您的DatabaseManager是一个单例.它的引用存储为静态变量.它在活动娱乐中幸存下来.它将一直存在直到该过程被杀死.

@H_301_0@因此,当您第二次运行queryAllinsects时,回调将被发送到MainActivity的旧实例,该实例不再可见.

@H_301_0@您不应该在DatabaseManager中保留对MainActivity的引用.这是一个内存泄漏,因为它不能被垃圾收集.

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