Android：如何滚动回RecyclerView项目，在项目被编辑和重新保存后？

Question

我有一个带有CardViews的RecyclerView列表，它运行良好。当用户在名为ActActivity的输入UI上输入数据时，创建CardViews。当用户稍后单击CardView以编辑原始数据时，onItemClick方法使用捕获适配器中正确CardView项位置的start方法再次启动ActActivity。

当用户单击UI上的Save按钮以保存编辑的数据时，ActActivity UI将关闭，并自动重新加载RecolyerView列表（MainActivity)，更新的CardView将显示在RecolyerView列表中。我的问题是重新加载时的RecyclerView总是滚动到CardView项目列表的顶部。我想要列表返回到原来的CardView（点击后进行编辑）。我需要在适配器中获取原始项的位置，并在重新创建时将其传递回RecyclerView。我需要让RecyclerView知道这个位置是针对刚刚编辑过的CardView，而不是新的CardView。对如何完成有什么想法吗？

mainactivity.java：

public class MainActivity extends AppCompatActivity
    ...
    void loadData(){
    SQLiteDB sqLiteDB = SQLiteDB.getInstance(this);

    List<Contact> contactList = new ArrayList<>();

    Cursor cursor = sqLiteDB.retrieve();
    Contact contact;
    cursor...
    Adapter.addAll(contactList);

    @Override
    public void onItemClick(int position, final View view) {
        cardview = (CardView) view;
        ActActivity.start(this, Adapter.getItem(position));
    }

public class ActActivity extends AppCompatActivity {
    ...
    private Contact contact;

    public static void start(Context context){
        Intent intent = new Intent(context, ActActivity.class);
        context.startActivity(intent);
    }

    public static void start(Context context, Contact contact){
        Intent intent = new Intent(context, ActActivity.class);
        // From the OnItemClick method in the MainActivity the RecyclerView item
        // position from the Adapter is passed into a putExtra bundle that the
        // intent carries to this Activity.  The data is then copied in the onCreate()
        // below using getIntent().getParcelableExtra(). So this is to update an
        // existing CardView item.
        intent.putExtra(ActActivity.class.getSimpleName(), contact);
        context.startActivity(intent);
    }

    @Override
    protected void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(layout.activ_act);

        // Fetch data from a parcelable object passed from the MainActivity.
        contact = getIntent().getParcelableExtra(ActActivity.class.getSimpleName());    
        ...
        // Update edited EditText lines to the data Model via contact
        contact.setDataInput(xEditText.getText().toString()); 
        // Update the data in the SQLite database.
        sqLiteDB.update(contact);
        ActActivity.this.finish();

public class Adapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private List<Contact> contactList;

    public Adapter(Context context) {
        this.context = context;
        this.contactList = new ArrayList<>();
    }

Logcat输出：

RuntimeException：无法恢复活动{com.example.jdw.v53/com.wimso.v053.MainActivity}：java.lang.nullPointerException位于Android.app.ActivityThread.PerformResumeActivity（ActivityThread.java:2575)位于Android.app.ActivityThread.HandleResumeActivity（ActivityThread.java:2603)位于Android.app.ActivityThread.HandleResumeActivity（ActivityThread.java:2603)位于Android.app.ActivityThread$H.在Android.app.Activity.PerformResume(Activity.java:5082)在Android.app.ActivityThread.PerformResumeActivity(ActivityThread.java:2565)在Android.app.ActivityThread.HandleResumeActivity(ActivityThread.java:2603) 在Android.app.ActivityThread$H.HandleMessage（ActivityThread.java:1237) 在android.os.handler.dispatchMessage(handler.java:99) 在android.os.looper.loop(looper.java:137) 在android.app.activityThread.main（activityThread.java:4745) 在java.lang.Reflect.Method.Invokenative（本机方法） 在java.lang.Reflect.Method.Invoke(method.java:511) 在com.android.internal.os.zygoteInit$methodandargscaller.run（zygoteInit.java:786) 在com.android.internal.os.zygoteinit.main（zygoteinit.java:553) 在Dalvik.System.NativeStart.Main（本机方法） 

Answer 1

可以使用Context.StartActivityForResult(intent,REQUEST_CODE)；启动ActActivity类，如下所示

 public static void start(Context context, Contact contact,int position){
        Intent intent = new Intent(context, ActActivity.class);
        // From the OnItemClick method in the MainActivity the RecyclerView item
        // position from the Adapter is passed into a putExtra bundle that the
        // intent carries to this Activity.  The data is then copied in the onCreate()
        // below using getIntent().getParcelableExtra(). So this is to update an
        // existing CardView item.
        intent.putExtra(ActActivity.class.getSimpleName(), contact);
        intent.putExtra("position", position);
        context.startActivityForResult(intent,2);
    }

ActActivity保存完数据后，可以使用setresult(intent)将结果中的适配器位置设置回主活动

一旦您在MainActivity中的OnActivityResult()中得到结果，您就会知道编辑后您已经回来了，因此您可以使用此方法滚动到该位置，如下所示

    // Call Back method  to get the Message form other Activity  
@Override  
protected void onActivityResult(int requestCode, int resultCode, Intent data)  
{  
    super.onActivityResult(requestCode, resultCode, data);  
    // check if the request code is same as what is passed  here it is 2  
    if(requestCode==2)  
    {  
        int position=data.getIntExtra("position", 0);  
        //do all your adapter resetting here for recyclerView
        linearLayoutManager.scrollToPositionWithOffset(position, 0);
    }  
}