Question

我有一个ArrayList，其中包含从Volley获取的自定义json对象。我希望能够在屏幕旋转上保存和恢复这些对象。我还想在屏幕旋转时保存并恢复当前的滚动位置。

我有一个粗略的想法，可以用onSaveInstanceState和onRestoreInstanceState来完成吗？

活动代码

delay()

提前致谢。

请注意How to save custom ArrayList on Android screen rotate?的副本。虽然该问题中的arraylist在活动中被宣布，但是我的网络中有凌空抽射。我不知道如何为我的arraylist实现它，否则不会问这个问题

Answer 1

事实上，这是the post you mentioned的副本。是的，列表是在该帖子中活动的onCreate（）中声明的，而您是异步进行的。但是，这个想法是一样的。

一旦有数据要发送，您可以在应用程序的任何位置保存和恢复数据。

在您的情况下，密钥是每次旋转设备时都不调用getData（）。如果已经在mPostItemsList中加载了数据，则通过onSaveInstanceState（）保存并恢复它，并在onCreate（）中获取保存状态的数据。如果该数据不存在，则调用getData（）。

public class MainActivity extends AppCompatActivity {

    private final String TAG = "MainActivity";
    private final String KEY_POST_ITEMS = "#postitems";

    //Creating a list of posts
    private List<PostItems> mPostItemsList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initializeViews();

        if (savedInstanceState != null && savedInstanceState.containsKey(KEY_POST_ITEMS)){
            mPostItemsList = savedInstanceState.getParcelableArrayList(KEY_POST_ITEMS);
        } else {
            //Initializing the postlist
            mPostItemsList = new ArrayList<>();

            if (NetworkCheck.isAvailableAndConnected(this)) {
                //Caling method to get data
                getData();
            } else {
                showNoNetworkDialog();
            }
        }

        mAdapter = new PostAdapter(mPostItemsList, this);
        recyclerView.setAdapter(adapter);

    }

    private void parseData(JSONArray array){
        mPostItemsList.clear();

        for(int i = 0; i<array.length(); i++) {
            PostItems postItem = new PostItems();
            JSONObject jsonObject = null;
            try {
                jsonObject = array.getJSONObject(i);
                postItem.setPost_title(jsonObject.getString(ConfigPost.TAG_POST_TITLE));
                postItem.setPost_body(jsonObject.getString(ConfigPost.TAG_POST_BODY));
            } catch (JSONException w) {
                w.printStackTrace();
            }

            mPostItemsList.add(postItem);
        }

        mAdapter.notifyDataSetchanged();

    }

编辑：我没有看到保存滚动位置的要求。请查看Emin Ayar's answer。此外，它的类似答案也在这里：How to save recyclerview scroll position。

Answer 2

您可以在活动中使用onConfigurationChanged来检测轮换变化。此外，您应该使用lastVisibleItemPosition跟踪layoutManager.findLastVisibleItemPosition()，当轮换更改时，您应该滚动到此位置。您需要使用recyclerView.setOnScrollListener()收听滚动条以保持lastVisibleItemPosition更新

public class MainActivity extends AppCompatActivity {

private final String TAG = "MainActivity";

//Creating and initializing list of posts
private List<PostItems> mPostItemsList = new ArrayList<>();;

//Creating Views
private RecyclerView recyclerView;
private RecyclerView.Adapter adapter;
private RecyclerView.LayoutManager layoutManager;
private ProgressDialog mProgressDialog;
private int lastVisibleItemPos = -1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d(TAG, "Device rotated and onCreate called");

    if (NetworkCheck.isAvailableAndConnected(this)) {
        //Caling method to get data and check if postList have value set before or not
        // because this part will be called on every rotation change, we are controlling this
        if (mPostItemsList.size() <= 0) {
            //Initializing Views
            recyclerView = (RecyclerView) findViewById(R.id.post_recycler);
            layoutManager = new LinearLayoutManager(this);
            recyclerView.setLayoutManager(layoutManager);

            adapter = new PostAdapter(mPostItemsList, this);

            recyclerView.setAdapter(adapter);
            getData();
        }

    } else {
        final Context mContext;
        mContext = this;
        final AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
        alertDialogBuilder.setTitle(R.string.alert_titl);
        alertDialogBuilder.setMessage(R.string.alert_mess);
        alertDialogBuilder.setPositiveButton(R.string.alert_posi, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                if (!NetworkCheck.isAvailableAndConnected(mContext)) {
                    alertDialogBuilder.show();
                } else {
                    getData();
                }


            }
        });
        alertDialogBuilder.setNegativeButton(R.string.alert_nega, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                finish();

            }
        });
        alertDialogBuilder.show();

    }

}

//This method will get data from the web api
private void getData(){


    Log.d(TAG, "getData called");
    //Showing progress dialog
    mProgressDialog = new ProgressDialog(MainActivity.this);
    mProgressDialog.setCancelable(false);
    mProgressDialog.setMessage(this.getResources().getString(R.string.load_post));
    mProgressDialog.show();

    //Creating a json request
    JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(ConfigPost.GET_URL,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    Log.d(TAG, "onResponse called");
                    //Dismissing the progress dialog
                    if (mProgressDialog != null) {
                        mProgressDialog.hide();
                    }
                    /*progressDialog.dismiss();*/


                    //calling method to parse json array
                    parseData(response);

                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {

                }
            });

    //Creating request queue
    RequestQueue requestQueue = Volley.newRequestQueue(this);

    //Adding request to the queue
    requestQueue.add(jsonArrayRequest);
}

//This method will parse json data
private void parseData(JSONArray array){
    Log.d(TAG, "Parsing array");

    for(int i = 0; i<array.length(); i++) {
        PostItems postItem = new PostItems();
        JSONObject jsonObject = null;
        try {
            jsonObject = array.getJSONObject(i);
            postItem.setPost_title(jsonObject.getString(ConfigPost.TAG_POST_TITLE));
            postItem.setPost_body(jsonObject.getString(ConfigPost.TAG_POST_BODY));

        } catch (JSONException w) {
            w.printStackTrace();
        }
        mPostItemsList.add(postItem);
    }

}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // set your adapter here with your data
    adapter = new PostAdapter(mPostItemsList, this);
    recyclerView.setAdapter(adapter);
}

@Override
public void onDestroy() {
    super.onDestroy();
    Log.d(TAG, "onDestroy called");
    if (mProgressDialog != null){
        mProgressDialog.dismiss();
        Log.d(TAG, "mProgress dialog dismissed");

    }
}

如何在配置更改时保存和恢复自定义arraylist

2 个答案: