problem with sending multiple data between activities android

Question

i want to send multiple data from activity WelcomeScreen to OpenBook here is my code

Sending

String a="pg558.sqlite";
        String b="pg558";
        Intent intent = new Intent(getApplicationContext(), OpenBook.class);
        intent.putExtra("db_name",a);
        intent.putExtra("book_name",b);
        intent.putExtra("chapter_number",3);
        intent.putExtra("page_number",1);
        startActivity(intent);

Recieving

Bundle b = getIntent().getExtras();
        DB_NAME= b.getString("db_name");
        BOOK_NAME= b.getString("book_name");
        CHAPTER_NUMBER= b.getInt("chapter_number",1);
        PAGE_NUMBER= b.getInt("page_number",1);

i'm getting runtime error

03-21 16:29:34.989: ERROR/AndroidRuntime(10651): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mireader/com.mireader.OpenBook}: java.lang.NullPointerException

Answer 1

try Intent intent = new Intent(this, OpenBook.class);

and Bundle b = getIntent();

Answer 2

no need to use bundle, just use this:

Receiving:
Intent i=getintent();
String ab=i.getextra("db_name");
String bc=i.getextra("book_name");
....

you will get your result

Answer 3

in line Intent intent = new Intent(getApplicationContext(), OpenBook.class); use this

Intent intent = new Intent(youractivity.class, OpenBook.class);

instead of using getApplicationContext() use MyActivityClass.this

Answer 4

I have given up on trying to keep track of multiple name/value pairs. You can create an immutable class (or use Parcels) as:

public final class PasswordState implements Serializable {
    private static final long serialVersionUID = 1L;
    public static final int MIN_PASSWORD_LENGTH= 8;
    public final int lengthKey;  // in bytes
    public final long timeExpire; // in milliseconds as a Calendar object
    public final boolean isValidKey;
    public final int timeoutType;
    public final String password;
    public final boolean isHashPassword;

    public PasswordState(int lengthKey,
            long timeExpire,
            boolean isValidKey,
            int timeoutType,
            String password,
            boolean isHashPassword){
        this.lengthKey= lengthKey;
        this.timeExpire= timeExpire;
        this.isValidKey= isValidKey;
        this.timeoutType= timeoutType;
        this.password= password;
        this.isHashPassword= isHashPassword;
    }

Then pass this in an intent to the child activity:

private void launchManagePassword() {
    Intent i= new Intent(this, ManagePassword.class); // no param constructor
    PasswordState outState= new PasswordState(lengthKey,timeExpire,isValidKey,timeoutType,"",model.getIsHashPassword());
    Bundle b= new Bundle();
    b.putSerializable("jalcomputing.confusetext.PasswordState", outState);
    i.putExtras(b);
    startActivityForResult(i,REQUEST_MANAGE_PASSWORD); // used for callback
}

Finally, retrieve the stateful object in the child activity:

     try {
        inPWState= (PasswordState) getIntent().getSerializableExtra("jalcomputing.confusetext.PasswordState");
        lengthKey= inPWState.lengthKey;
        timeoutType= inPWState.timeoutType;
        isValidKey= inPWState.isValidKey;
        timeExpire= inPWState.timeExpire;
        isHashPassword= inPWState.isHashPassword;
        // password= inPWState.password; // not required
    } catch(Exception e){
        lengthKey= PasswordState.MIN_PASSWORD_LENGTH;
        timeoutType= TIMEOUT_NEVER;
        isValidKey= true;
        timeExpire= LONG_YEAR_MILLIS;
        isHashPassword= false;
    }

JAL

Answer 5

在您的问题中， activityclass.class表示您实际上在其中调用了用于将数据发送到第二个活动的意图和捆绑包的类。