java—每次我尝试在应用程序中按book时都会出现一个异常

ia2d9nvy  于 2021-07-06  发布在  Java
关注(0)|答案(1)|浏览(290)
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mylibary, PID: 16960
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mylibary/com.example.mylibary.BookActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.example.mylibary.BookActivity.handleCurrentlyReadingBooks(BookActivity.java:100)
        at com.example.mylibary.BookActivity.onCreate(BookActivity.java:42)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
I/Process: Sending signal. PID: 16960 SIG: 9

班级

package com.example.mylibary;
    import androidx.appcompat.app.AppCompatActivity;
    import android.content.Intent;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    import android.widget.ImageView;
    import android.widget.TextView;
    import android.widget.Toast;

    import com.bumptech.glide.Glide;

    import java.util.ArrayList;

    public class BookActivity extends AppCompatActivity {

public static final String BOOK_ID_KEY = "bookId";

private Button btnAddCurrentlyReading, btnAddWishList, btnAddAllReadyRead, btnAddToFavorites;
private TextView txtBookName, txtLalala, txtAuthor, txtNikita, txtPages, txtPagesNumber, 
txtShortDesk, txtLongDesk;
private ImageView imgBook;

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

    initViews();

    Intent intent = getIntent();
    if (null != intent) {
        int bookId = intent.getIntExtra(BOOK_ID_KEY, -1);
        if (bookId != -1) {
            Books incomingBook = Utils.getInstance().getBookById(bookId);
            if (null != incomingBook) {
                setData(incomingBook);
                handleAllReadyRead(incomingBook);
                handleCurrentlyReadingBooks(incomingBook);
                handleWantToReadBooks(incomingBook);
                handleFavoriteBooks(incomingBook);
            }
        }
    }

}

private void handleFavoriteBooks(final Books books){
    Utils.getInstance();
    ArrayList<Books> FavoriteBooks = Utils.getFavoritesBooks();

    boolean existInFavoriteBooks = false;

    for (Books b: FavoriteBooks){
        if (b.getId() == books.getId()) {
            existInFavoriteBooks = true;
            break;
        }

    }
    if (existInFavoriteBooks){
        btnAddToFavorites.setEnabled(false);
    }else{
        btnAddToFavorites.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (Utils.getInstance().addToFavoritesBooks(books)){
                    Toast.makeText(BookActivity.this, "book add successfully", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(BookActivity.this, FavoritesBooksActivity.class);
                    startActivity(intent);
                }else{
                    Toast.makeText(BookActivity.this, "try again", Toast.LENGTH_SHORT).show();
                }

            }
        });
    }
}

private void handleCurrentlyReadingBooks(final Books books){
    Utils.getInstance();
    ArrayList<Books> CurrentlyReadingBooks = Utils.getCurrentlyReadingBooks();

    boolean existInCurrentlyReadingBooks = false;

    for (Books b: CurrentlyReadingBooks){
        if (b.getId() == books.getId()) {
            existInCurrentlyReadingBooks = true;
            break;
        }

    }
    if (existInCurrentlyReadingBooks){
        btnAddCurrentlyReading.setEnabled(false);
    }else{
        btnAddCurrentlyReading.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (Utils.getInstance().addCurrentlyReadingBooks(books)){
                    Toast.makeText(BookActivity.this, "book add successfully", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(BookActivity.this, CurrentlyReadingActivity.class);
                    startActivity(intent);
                }else{
                    Toast.makeText(BookActivity.this, "try again", Toast.LENGTH_SHORT).show();
                }

            }
        });
    }
}

private void handleWantToReadBooks(final Books books){
    Utils.getInstance();
    ArrayList<Books> WantToReadBooks = Utils.getWantToReadBooks();

    boolean existInWantToReadBooks = false;

    for (Books b: WantToReadBooks){
        if (b.getId() == books.getId()) {
            existInWantToReadBooks = true;
            break;
        }

    }
    if (existInWantToReadBooks){
        btnAddWishList.setEnabled(false);
    }else{
        btnAddWishList.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (Utils.getInstance().addWantToReadBooks(books)){
                    Toast.makeText(BookActivity.this, "book add successfully", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(BookActivity.this, WantToReadActivity.class);
                    startActivity(intent);
                }else{
                    Toast.makeText(BookActivity.this, "try again", Toast.LENGTH_SHORT).show();
                }

            }
        });
    }
}

private void handleAllReadyRead(final Books books){
    Utils.getInstance();
    ArrayList<Books> AllReadyReadBooks = Utils.getAllReadyReadBooks();

    boolean existInAllReadyReadBooks = false;

    for (Books b: AllReadyReadBooks){
        if (b.getId() == books.getId()) {
            existInAllReadyReadBooks = true;
            break;
        }

    }
    if (existInAllReadyReadBooks){
        btnAddAllReadyRead.setEnabled(false);
    }else{
        btnAddAllReadyRead.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (Utils.getInstance().addAllReadyReadBook(books)){
                    Toast.makeText(BookActivity.this, "book add successfully", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(BookActivity.this, AllReadyReadBooksActivity.class);
                    startActivity(intent);
                }else{
                    Toast.makeText(BookActivity.this, "try again", Toast.LENGTH_SHORT).show();
                }

            }
        });
    }
}

private void setData(Books books) {
    txtLalala.setText(books.getName());
    txtNikita.setText(books.getAuthor());
    txtPagesNumber.setText(String.valueOf(books.getPages()));
    txtShortDesk.setText(books.getShortDesk());
    txtLongDesk.setText(books.getLongDesk());
    Glide.with(this).asBitmap()
            .load(books.getImageUrl())
            .into(imgBook);

}

private void initViews() {
    btnAddCurrentlyReading = findViewById(R.id.btnCurrentlyReading);
    btnAddWishList = findViewById(R.id.btnAddWishList);
    btnAddAllReadyRead =findViewById(R.id.btnAddAllReadyRead);
    btnAddToFavorites = findViewById(R.id.btnAddToFavorites);
    txtBookName =findViewById(R.id.txtBookName);
    txtLalala = findViewById(R.id.txtLalala);
    txtAuthor = findViewById(R.id.txtAuthor);
    txtNikita =findViewById(R.id.txtNikita);
    txtPages = findViewById(R.id.txtPages);
    txtPagesNumber = findViewById(R.id.txtPagesNumber);
    txtShortDesk = findViewById(R.id.txtShortDesk);
    txtLongDesk = findViewById(R.id.txtLongDesk);
    imgBook = findViewById(R.id.imgBook);
}

我做了一个图书馆应用程序，每次我按这本书我都想看看，这给了我这个例外
这里有一些代码

Javaandroid

1条答案

按热度按时间
vawmfj5a

vawmfj5a1#

findViewById() -返回“如果找到具有给定id的视图，否则返回null”，这意味着 R.id.btnCurrentlyReading 找不到
看看你写得好不好

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