We are going to learn how to bookmark the articles so that we can easily access them in our Bookmark screen later. The process is simple. We are going to save post id to Asyncstorage from the SinglePost screen and then fetch the articles on the bookmark screen. Here, we are going to add the bookmark icon to the SinglePost screen and configure its functionality.
But first, we need to define the state variable called 
already_bookmark
 in the 
SinglePost.js
file in order to handle the showing of bookmark enabled or disabled icon. For that, we need to use the code from the following code snippet:
 constructor(props) {
        super(props);
        this.state = {
          isloading: true,
          post: [],
          already_bookmark: false,
        };
      }
Then, we need to add the Bookmark icon to the screen. For that, we need to use the code from the following code snippet:
<List.Item
                 title={`Published on ${moment(
                   post[0].date,
                   'YYYYMMDD',
                 ).fromNow()}`}
                 right={props => {
                   if (this.state.already_bookmark == true) {
                     return (
                       <TouchableOpacity
                         onPress={() => this.removeBookMark(post[0].id)}>
                         <FontAwesome name="bookmark" size={30} />
                       </TouchableOpacity>
                     );
                   } else {
                     return (
                       <TouchableOpacity
                         onPress={() => this.saveBookMark(post[0].id)}>
                         <FontAwesome name="bookmark-o" size={30} />
                       </TouchableOpacity>
                     );
                   }
                 }}
               />
Here, we have displayed the bookmark icon template based on the
already_bookmark
 state. The template has the 
TouchableOpacity
component that wraps the 
FontAwesome
 component. In the onPress events we have called the 
removeBookMark
and 
saveBookMark
 function. These functions are use to bookmark the article or remove the bookmark from the article.
Hence, we will get the following result in the emulator screen:
Next, we need to use the AsyncStorage component from the
@react-native-community/async-storage package. For that, we need to use install the package first. In order to install the package we need to run the command from the following code snippet:
  yarn add @react-native-community/async-storage
We can get the information as well as the installation instruction from the
package documentation.
Now, we need to import this package into our Bookmark.js file as shown in the code snippet below:
 import AsyncStorage from '@react-native-community/async-storage';

Save Bookmark

Here, we are going to implement the saveBookMark function. For that, we need to define the function first as shown in the code snippet below:
  saveBookMark = async post_id => {
        this.setState({already_bookmark: true});
      };
Here, we have taken the parameter as post id with asynchronous execution of the function. Then, we have set the 
already_bookmark
state variable to true.
Now, we need to save the post id of the bookmarked post to the 
AsyncStorage
. For that, we need to use the code from the following code snippet:
  saveBookMark = async post_id => {
             this.setState({already_bookmark: true});
             let bookmark = [];
             bookmark.push(post_id);
             AsyncStorage.setItem('bookmark', JSON.stringify(bookmark));

     };
Here, we have defined a new array called bookmark and pushed the post id value into it. Then, we have made use of the setItem function of the 
AsyncStorage
to save the bookmark. We have saved the bookmark array as a JSON value.
Next, we need to prevent the duplicate bookmarks of the same article. For that, we need to use the code from the following code snippet:
  saveBookMark = async post_id => {
        this.setState({already_bookmark: true});
        await AsyncStorage.getItem('bookmark').then(token => {
          const res = JSON.parse(token);
          if (res !== null) {
            let data = res.find(value => value === post_id);
            if (data == null) {
              res.push(post_id);
              AsyncStorage.setItem('bookmark', JSON.stringify(res));
            }
          } else {
            let bookmark = [];
            bookmark.push(post_id);
             AsyncStorage.setItem('bookmark', JSON.stringify(bookmark));
          }
        });
      };
Here, we get the bookmark data and then parse it to an array called res. Then, if we have the bookmark data, we search the post_id for the current post. If the post does not exist in the bookmark, then we can add the bookmark to it and prevent duplicate bookmarks. The third case is for the users who have not made any bookmarks yet. Hence, we can normally apply and save the bookmarks using the saveBookMark function.

Summary

In this chapter, we learned how to implement the UI and functionality of the bookmark button using the 
AsyncStorage
 module. Using it, we implemented the function to save method
This series intends to show how I build an app to serve content from my WordPress blog by using react-native. Since my blog is talking about react-native, the series and the articles are interconnected. We will learn how to set-up many packages that make our lives comfortable and learn how to deal with WordPress APIs. Here, the most prominent features talked about in the book are the dark theme, offline mode, infinite scroll and many more. You can discover much more in this series. this inspiration to do this tutorial series came from the React Native App Templates from instamobile