java - 使用 Firebase 刷新列表的最佳方法是什么

Question

我目前在项目中更新列表的方式显然不是应用程序的标准。如何刷新列表而不清除它？

这段代码写得很好，没有任何中断；但是，一旦用户完成编辑，列表就会被清除并刷新，使用户返回到列表顶部。刷新数据时的最佳实践是什么，特别是当其他用户正在编辑数据而不中断当前用户时。

写作:

protected void addStep() {
String stepID = Database.push().getKey();
step newStep = new step(recipeID, stepID, "stepImage", "","");
Database.child(stepID).setValue(newStep);
getData();

}

适配器:

package asdasd.asd;

import android.app.Activity;
import android.support.annotation.NonNull;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

/**
 * This class is the class responsible for handling the lists of steps that the user will see during the creator phase.
 * It works by setting an array adapter which uses the fragment_steps layout displaying it on a list within the StepActivity
 * On text listeners are on each of the fields, when the user edits one of the fields, the program waits 600ms, and then uploads the
 * data to the database;
 * this refreshes the list TODO change the way the list refreshes in the instance of the creator; perhaps add a delay of 1 minuite before refresh, and or if a new step has been added
 * A timer is responsible for this delay. The setting of data is to a specific path; being the recipe -> step -> long/shortText field.
 */

public class stepList extends ArrayAdapter<step>{
    private Activity context;
    private List<step> steps;
    private DatabaseReference database;
    private Timer timer1,timer2;

    public stepList(Activity context, List<step> steps) {
        super(context, R.layout.fragment_step, steps);
        this.context = context;
        this.steps = steps;
    }

    @NonNull
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        //get database
        database = FirebaseDatabase.getInstance().getReference("steps");

        //init Layout inflater
        LayoutInflater inflater = context.getLayoutInflater();

        //step
        View listViewItem = inflater.inflate(R.layout.fragment_step,null,true);

        //step objects
        final TextView descriptionText = (TextView) listViewItem.findViewById(R.id.stepRecipeShortText);
        final TextView longDescriptionText = (TextView) listViewItem.findViewById(R.id.stepRecipeLongText);
        ImageView stepImage = listViewItem.findViewById(R.id.stepImage);
        //init step
        final step step = steps.get(position);

        //get stepID
        final String stepID = step.getStepID();

        //Set Data
        descriptionText.setText(step.getStepDescription());
        longDescriptionText.setText(step.getStepLongDescription());

        //TODO If user has uploaded an image, then use that, else then use default

        //Add listener to descriptionText so that when a user edits the fields, it is uploaded to the same step in the database
        descriptionText.addTextChangedListener(new TextWatcher() {

            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                // user is typing: reset already started timer (if existing)
                if (timer1 != null) {
                    timer1.cancel();
                }
            }
            @Override
            public void afterTextChanged(Editable s) {
                timer1 = new Timer();
                timer1.schedule(new TimerTask() {
                    @Override
                    public void run() {
                        String newDescriptionText = descriptionText.getText().toString();
                        addToDatabase(stepID,"stepDescription", newDescriptionText);
                    }
                }, 600);
            }
        });
        //Add listener to LongDescriptionText so that when a user edits the fields, it is uploaded to the same step in the database
        longDescriptionText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                // user is typing: reset already started timer (if existing)
                if (timer2 != null) {
                    timer2.cancel();
                }
            }
            @Override
            public void afterTextChanged(Editable s) {
                timer2 = new Timer();
                timer2.schedule(new TimerTask() {
                    @Override
                    public void run() {
                        String newLongDescriptionText = longDescriptionText.getText().toString();
                        addToDatabase(stepID, "stepLongDescription", newLongDescriptionText);
                    }
                }, 600);
            }
        });
        return listViewItem;
    }
    //Add the data the user is entering to the database; there is a 600ms delay on the period between the user stopping typing and the data being updated.
    private void addToDatabase(String id, String location, String text) {
        database.child(id).child(location).setValue(text);
    }
}

获取:

public void getData() {
        //receives all the recipes and adds them to the list
        Database.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                //Clear the list
                listStepsList.clear();
                //Iterate through the nodes
                for(DataSnapshot stepSnapshot : dataSnapshot.getChildren()){
                    //get recipe
                    step step = stepSnapshot.getValue(step.class);
                    //add step to list, if it is apart of the same recipe.
                    if(step.getRecipeID().equals(recipeID)) {
                        listStepsList.add(step);
                    }
                }
                //create Adapter
                stepList stepAdapter = new stepList(StepActivity.this, listStepsList);
                //Attatch adapter to listview
                viewStepsList.setAdapter(stepAdapter);
                stepAdapter.notifyDataSetChanged();
            }
            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

Answer 1

我假设只要数据库发生变化，您就会看到“大爆炸”/闪光。如果是这样，那是因为您正在更新整个列表，即使数据中只更改了单个项目。

为了改进这一点，您需要更精细地更新适配器以进行更改。为此，您可以附加一个 ChildEventListener，它会触发数据结构中较低一级的事件。因此，假设将一个新节点添加到您的列表中，您将得到一个仅包含一个新节点的 onChildAdded 调用，而不是重建整个列表来添加一个节点。然后，您将更新 listStepsList 而不是重建它，并告诉适配器有关更改的信息。

举个例子，我建议查看 FirebaseUI，如 adapters in there都使用这种模式。他们从共同的FirebaseArray class构建它观察数据库，然后使用适配器类将数组粘合到 UI。例如，这里是how FirebaseRecyclerAdapter connects the changes in the database to minimal updates to the view .