在 sharedPreferences 中存储位置列表，并在另一个活动中检索

Question

我想做类似this 的事情，我使用了cardview 和recyclerview。我在下面添加了最喜欢的按钮卡片视图，您可以看到完整的代码。在 recyclerview 适配器中，我根据位置打印 Toast 并且它工作正常，现在我需要将位置的 int 值保存在 arraylist 中的共享首选项中，并在下一个意图中显示这些 arraylist。

这是我的 recyclerview 适配器

public void onBindViewHolder(NameViewHolder holder, final int position) {
    holder.textView.setText(names.get(position).textView);
    holder.favourite.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(view.getContext());
            SharedPreferences.Editor editor = sp.edit();
            editor.putInt("key", position);  //may be or may not be.
            //add code here to save position in array
            Toast.makeText(view.getContext(),"Fav "+position,Toast.LENGTH_SHORT).show();
        }
    });

cardview.xml

<?xml version="1.0" encoding="utf-8"?>

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/cardview"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="3dp"
android:orientation="vertical"
app:cardBackgroundColor="@android:color/transparent"
app:cardCornerRadius="8dp"
app:cardElevation="3dp"
app:cardPreventCornerOverlap="false"
app:cardUseCompatPadding="true">

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:paddingLeft="20dp"
    android:paddingTop="3dp"
    android:textAlignment="center"
    android:textColor="#ff9901"
    android:textSize="35sp"
    android:textStyle="italic" />

<RelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <ImageButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:id="@+id/favourite"
        android:src="@drawable/star"
        android:background="@android:color/transparent"
        />
</RelativeLayout>
</android.support.v7.widget.CardView>

提供我从首选项中获取数组列表以及如何在 ListView 中使用。

Answer 1

首先，考虑通过intent以bundle的形式传递数据。如果您在关闭应用后不需要存储此信息，请使用该方式。

如果您还想通过重新运行应用程序来保存数据，那么 SharedPreferences 就可以了，这里是代码，您如何实现此功能。首先让我们编写帮助您恢复项目并使用它们更新适配器的 sn-p：

private static final String CHECKED_ITEMS_REF = "checked_items";
private SharedPreferences sharedPreferences = getContext().getSharedPreferences("MySharedPrefs", MODE_PRIVATE);

private void restoreAdapterState(RecyclerView.Adapter adapter) {
    Set<String> savedCheckedItems = sharedPreferences.getStringSet(CHECKED_ITEMS_REF, new HashSet<>());
    List<Integer> checkedPositions = convertToCheckedItems(savedCheckedItems);
    for (Integer position : checkedPositions) {
        //update somehow info about checked items, for example in 
        //adapter you can store set of checked positions and in
        //onBindViewHolder function check is ViewHolder position
        //contained in you set
        adapter.notifyItemChanged(position);
    }
}

private List<Integer> convertToCheckedItems(Set<String> checkedItems) {
    List<Integer> result = new ArrayList<>();
    for(String itemPositionStr : checkedItems) {
        int position = Integer.parseInt(itemPositionStr);
        result.add(position);
    }

    return result;
}

请注意，您可以在评论中遵循我的建议，然后 restoreAdapterState 将被修改：

private void restoreAdapterState(MultiCheckedAdapter adapter) {
    Set<String> savedCheckedItems = sharedPreferences.getStringSet(CHECKED_ITEMS_REF, new HashSet<>());
    List<Integer> checkedPositions = convertToCheckedItems(savedCheckedItems);
        adapter.setCheckedPositions(new HashSet<Integer>(checkedPositions));
}

在MultyCheckedAdapter 中，您将拥有类似的内容：

private Set<Integer> checkedPositions = new HashSet<>();

public setCheckedPositions(Set<Integer> checkedPositions) {
    this.checkedPositions = checkedPositions;
    for (Integer position : checkedPositions) {
        adapter.notifyItemChanged(position);
    }
}

...

@Override
public void onBindViewHolder(MyHolder holder, final int position) {
    if (checkedPositions.contains(position)) {
        //use one binding
    } else {
        //use another binding
    }
}

...

那么你需要改变你的sn-p：

private Set<Integer> checkedPositions = new HashSet<>();

public void onBindViewHolder(NameViewHolder holder, final int position) {
    holder.textView.setText(names.get(position).textView);
    holder.favourite.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //check somehow is current item checked or not.
            //for example store set of checked items in adapter
            //let's say it declaration is Set<Integer> checkedItems;
            if (checkedPositions.contains(position)) {
                checkedPositions.remove(position);
                removeCheckedItem(position);
            } else {
                checkedPositions.add(position);
                saveCheckedItem(position);
            }
        }
    });
}

private void saveCheckedItem(int position) {
    Set<String> savedCheckedItems = sharedPreferences.getStringSet(CHECKED_ITEMS_REF, new HashSet<>());
    String positionStr = String.valueOf(position);
    if (!savedCheckedItems.contains(positionStr)) {
        savedCheckedItems.add(positionStr);
        sharedPreferences.edit().putStringSet(CHECKED_ITEMS_REF, savedCheckedItems).apply();
    }
}

private void removeCheckedItem(int position) {
    Set<String> savedCheckedItems = sharedPreferences.getStringSet(CHECKED_ITEMS_REF, new HashSet<>());
    String positionStr = String.valueOf(position);
    if (savedCheckedItems.contains(positionStr)) {
        savedCheckedItems.remove(positionStr);
        sharedPreferences.edit().putStringSet(CHECKED_ITEMS_REF, savedCheckedItems).apply();
    }
}

Answer 2

您可以为此目的使用 StringBuilder。根据项目单击追加/替换，然后将其作为字符串保存到共享首选项。

    public void onBindViewHolder(NameViewHolder holder, final int position) {
   StringBuilder sb = new StringBuilder(sp.getStringPreference("key", ""))
    holder.textView.setText(names.get(position).textView);
    holder.favourite.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(view.getContext());
            SharedPreferences.Editor editor = sp.edit();
            sb.append(position);
            editor.putString("key", sb.toString()); 
            Toast.makeText(view.getContext(),"Fav "+position,Toast.LENGTH_SHORT).show();
        }
    });

可以使用 Integer.parseInt(s.charAt(index)); 从 String 中检索整数项。 但是，如果您只需要将值传递给下一个活动并且以后不需要，那么您可以使用 ArrayList 并通过 Intent 传递它。

Answer 3

这一行之后：

editor.putInt("key", position);

这样写：

editor.apply();

我认为您应该将这些值添加到列表中，然后将列表作为参数传递给另一个活动，这将是一种更好的方法。

编辑 2

// take a global string 
String positions = "";

 public void onClick(View view) {
            SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(view.getContext());
            SharedPreferences.Editor editor = sp.edit();
            /*   here first concat the current item position with the string, then put that in the pref  */
            positions = positions + position + " ";
            editor.putString("key", positions); 

        }



//in the next activity, 
String key = sp.getString("key");
String[] positions = key.split(" ");
// Now you have all the positions in the next activity and its in the String datatype
// if you wanna int datatype there, parse it through Integer.parseInt(string).

Answer 4

用它来存储

SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(view.getContext().MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
editor.putInt("key", position);  //may be or may not be.
editor.commit;

并在您的其他活动中使用它来检索

SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(view.getContext().MODE_PRIVATE);
            int position=sp.getInt("key");

你也可以试试这个 就像在你的活动 A 创建Activity B的Intent

Intent intent =new Intent(A.this,B.class);
intent.putExtra("key",position);
startActivity(intent);

在你的活动 B

Intent intent= getIntent();
int position Integer.parseInt(intent.getExtras().get("key"));

编辑

使用数组列表并将其从一个活动转移到另一个活动

 ArrayList<Integer> mThumbIds=new ArrayList<Integer>() ;
    mThumbIds.add(R.drawable.sample_0);
            mThumbIds.add(R.drawable.sample_1);
            mThumbIds.add(R.drawable.sample_2);
            mThumbIds.add(R.drawable.sample_3);
            mThumbIds.add(R.drawable.sample_4);
            mThumbIds.add(R.drawable.sample_5);
            mThumbIds.add(R.drawable.sample_6);
            mThumbIds.add(R.drawable.sample_7);
 listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                ArrayList list=mThumbIds;
                Intent intent= new Intent(A.this,B.class);
                       intent.putExtra("list",mThumbIds);
                intent.putExtra("position",position);
                intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
               //   overridePendingTransition(R.anim.hold,R.anim.slide_in_left);
                    startActivity(intent);




            }
        });

现在在你的活动 B 中使用它

    Intent intent =getIntent();


        int position=Integer.parseInt(intent.getExtras().get("position").toString());
        ArrayList<Integer> list= (ArrayList<Integer>) intent.getExtras().get("list");

int current_position=list.get(position)