Android: 查看返回 null

Question

我正在尝试获取联系人并将其显示在列表中。我为此使用 RxPermissions。这里的问题是当我第一次允许视图 returns null 的权限并显示空列表时，即使列表中有项目。但是当我回到之前的 activity 并回来时它工作正常。

ContactsFragment.kt

override fun onResume() {
        super.onResume()
        if (isPermissionGranted) {
            Timber.d("Permission is granted")
            contactsPresenter.fetchContacts(context)
            noPermissionsWarning.visibility = View.GONE
        } else {
            noPermissionsWarning.visibility = View.VISIBLE
            showContactList(ArrayList()) // Show empty list when permissions not granted
        }
    }
private fun askPermissions() {
    rxPermissions
            .request(android.Manifest.permission.GET_ACCOUNTS,
                    android.Manifest.permission.READ_CONTACTS,
                    android.Manifest.permission.WRITE_CONTACTS)
            .subscribe { permissionGranted ->
                isPermissionGranted = permissionGranted
            }
}



override fun showContactList(selectedContacts: ArrayList<Contact>) {
        contactAdapter = ContactListAdapter(selectedContacts, this, context)
        val layoutManager = LinearLayoutManager(this.context)
        contactsRecyclerView?.layoutManager = layoutManager
        contactsRecyclerView?.addItemDecoration(DividerItemDecoration(
                contactsRecyclerView?.context,
                DividerItemDecoration.VERTICAL
        ))
        contactsRecyclerView?.adapter = contactAdapter
    }

ContactsPresenter.kt

override fun takeView(view: ContactsContract.View, context: Context?) {
        super.takeView(view)
        contactList.clear()
        tempContactList.clear()
    }

    override fun fetchContacts(context: Context?) {
        contactManager.getContacts(context)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe({
                    it.let {
                        tempContactList.addAll(it.sortedWith(compareBy { it.userName }))
                        contactList.addAll(it.sortedWith(compareBy { it.userName }))
                        view?.showContactList(contactList)// this view is null at first
                    }
                }, {

                }).addDisposableTo(disposable)
    }

我会在这里遗漏什么。

谢谢

Answer 1

看起来你应该在这一行之后立即获取你的联系人：

isPermissionGranted = permissionGranted

Answer 2

我通过在 onResume() 和 onViewCreated() 中附加视图解决了这个问题。感谢大家的帮助

很长一段时间后，我发现我正在清理 onPause() 上的一次性用品，在我的情况下，这应该在 onDestroy() 内完成。我写了解决方案以防它对某些人有帮助

Answer 3

在检查是否授予权限时调用您的方法

 if (ContextCompat.checkSelfPermission(MainActivity.this,
            Manifest.permission.WRITE_EXTERNAL_STORAGE) == 
                      PackageManager.PERMISSION_GRANTED) {
Filtering filtering=new Filtering();
//contactFetch method  here
    } else {         

     Permission.requestStoragePermission(MainActivity.this,
                    STORAGE_PERMISSION_CODE);
    }

之后当你请求权限时......

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    if (requestCode == STORAGE_PERMISSION_CODE)  {
        if (grantResults.length > 0 && grantResults[0] == 
                   PackageManager.PERMISSION_GRANTED) {
            Filtering filtering=new Filtering();
            //Again your fetching method
        } else {
            Toast.makeText(this, "Permission DENIED", Toast.LENGTH_SHORT).show();
            Permission.requestStoragePermission(MainActivity.this,
                                  STORAGE_PERMISSION_CODE);
        }
    }
}

尝试这个我不确定，但我认为它会对你有所帮助

Android: 查看返回 null

Android: View returning null

mvp

android

android-fragments

kotlin

rxpermissions