Question

我发现了许多与我的问题相关的问题，但我无法解决我的问题，这就是我发布此问题的原因。我第一次使用firebase作为实时数据库。使用下面的代码，我试图通过单击添加按钮将值保存到firebase。但我的应用程序stops.Here是我的logcat

FATAL EXCEPTION: main

    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
        at com.example.xyz.finance.MainActivity.addArtist(MainActivity.java:88)
        at com.example.xyz.finance.MainActivity.access$000(MainActivity.java:25)
        at com.example.xyz.finance.MainActivity$1.onClick(MainActivity.java:75)
        at android.view.View.performClick(View.java:5721)
        at android.widget.TextView.performClick(TextView.java:10936)
        at android.view.View$PerformClick.run(View.java:22620)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:7406)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Artist模态类

@IgnoreExtraProperties
public class Artist {
    private String artistId;
    private String artistName;
    private String artistGenre;

    public Artist(){
        //this constructor is required
    }

    public Artist(String artistId, String artistName, String artistGenre) {
        this.artistId = artistId;
        this.artistName = artistName;
        this.artistGenre = artistGenre;
    }

    public String getArtistId() {
        return artistId;
    }

    public String getArtistName() {
        return artistName;
    }

    public String getArtistGenre() {
        return artistGenre;
    }
}

Track模态类

public class Track {
    private String id;
    private String trackName;
    private int rating;

    public Track() {

    }

    public Track(String id, String trackName, int rating) {
        this.trackName = trackName;
        this.rating = rating;
        this.id = id;
    }

    public String getTrackName() {
        return trackName;
    }

    public int getRating() {
        return rating;
    }
}

MainActivity

public class MainActivity extends AppCompatActivity {

//we will use these constants later to pass the artist name and id to another activity
public static final String ARTIST_NAME = "com.example.xyz.finance.artistname";
public static final String ARTIST_ID = "com.example.xyz.finance.artistid";

        //view objects
        EditText editTextName;
        Spinner spinnerGenre;
        Button buttonAddArtist;
        ListView listViewArtists;

        //a list to store all the artist from firebase database
        List<Artist> artists;

        //our database reference object
        DatabaseReference databaseArtists;



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

        //getting the reference of artists node
        databaseArtists = FirebaseDatabase.getInstance().getReference("finance");



        //getting views
        editTextName = (EditText) findViewById(R.id.editTextName);
        spinnerGenre = (Spinner) findViewById(R.id.spinnerGenres);
        listViewArtists = (ListView) findViewById(R.id.listViewArtists);

        buttonAddArtist = (Button) findViewById(R.id.buttonAddArtist);


        //list to store artists
        artists = new ArrayList<>();


        //adding an onclicklistener to button
        buttonAddArtist.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
        //calling the method addArtist()
        //the method is defined below
        //this method is actually performing the write operation

        addArtist();
        }
        });
        }

    /*
    * This method is saving a new artist to the
    * Firebase Realtime Database
    * */
private void addArtist() {
        //getting the values to save

        String name = editTextName.getText().toString().trim();
        String genre = spinnerGenre.getSelectedItem().toString();

        //checking if the value is provided

        if (!TextUtils.isEmpty(name) ) {

        //getting a unique id using push().getKey() method
        //it will create a unique id and we will use it as the Primary Key for our Artist

        String id = databaseArtists.push().getKey();

        //creating an Artist Object



        Artist artist = new Artist(id, name, genre);
        //Saving the Artist
        databaseArtists.child(id).setValue(artist);

        //setting edittext to blank again
        editTextName.setText("");

        //displaying a success toast
        Toast.makeText(this, "Artist added", Toast.LENGTH_LONG).show();
        } else {
        //if the value is not given displaying a toast
        Toast.makeText(this, "Please enter a name", Toast.LENGTH_LONG).show();
        }
        }
        }

Answer 1

请尝试在“编辑开始”和“编辑结束”
之间编写代码

private void addArtist() {
        //getting the values to save

        String name = editTextName.getText().toString().trim();
        String genre = spinnerGenre.getSelectedItem().toString();

        //checking if the value is provided

        if (!TextUtils.isEmpty(name) ) {

        //getting a unique id using push().getKey() method
        //it will create a unique id and we will use it as the Primary Key for our Artist

        String id = databaseArtists.push().getKey();

        //creating an Artist Object

//Edit Started
          Map<String, Object> params = new HashMap<>();
          params.put("id", id);
          params.put("name", name);
          params.put("genre",genre);

        //Saving the Artist
        databaseArtists.child(id).updateChildren(params)

// Edit Ended

        //setting edittext to blank again
        editTextName.setText("");

        //displaying a success toast
        Toast.makeText(this, "Artist added", Toast.LENGTH_LONG).show();
        } else {
        //if the value is not given displaying a toast
        Toast.makeText(this, "Please enter a name", Toast.LENGTH_LONG).show();
        }
        }
        }

模态类作为null传递

1 个答案: