CODEWITHSUNDEEP
javaandroidandroid-intentnullpointerexceptionstartactivityforresult
Genadiy Naumov
Genadiy Naumov

Reputation: 45

Can't call another activity using Intent

I'm new in Android and just trying to figure out how to work with method onActivityResult. I want to click button on mainActivity, go to another actvivity, enter name and return to mainActivity. But I have troubles with running app. I always have get this error:

java.lang.NullPointerException: Attempt to invoke virtual method...

09-20 22:14:32.212 30617-30617/com.genaepic.p029_simpleactivityresult E/AndroidRuntime:

FATAL EXCEPTION: main Process: com.genaepic.p029_simpleactivityresult, PID: 30617 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.genaepic.p029_simpleactivityresult/com.genaepic.p029_simpleactivityresult.NameActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) at android.app.ActivityThread.-wrap12(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.genaepic.p029_simpleactivityresult.NameActivity.onCreate(NameActivity.java:22) at android.app.Activity.performCreate(Activity.java:6679) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)  at android.app.ActivityThread.-wrap12(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6119)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

My main activity:

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView textView;
    Button button;


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

        textView = (TextView) findViewById(R.id.tv_main);
        button = (Button) findViewById(R.id.btn_iputName);
        button.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        Intent intent = new Intent(this, NameActivity.class);
        startActivityForResult(intent, 1);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if(data == null) {
            return;
        }
        String name = data.getStringExtra("name");
        textView.setText("Your name is " + name);
    }
}

My second activity:

public class NameActivity extends AppCompatActivity implements View.OnClickListener {

EditText editText;
Button button;

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

    editText = (EditText) findViewById(R.id.et_name);
    button = (Button) findViewById(R.id.btn_iputName);
    button.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    Intent intent = new Intent();
    intent.putExtra("name", editText.getText().toString());
    setResult(RESULT_OK, intent);
    finish();
}

}

My xml code for mainActivity:

<Button
    android:id="@+id/btn_iputName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="input your name"
    tools:layout_constraintTop_creator="1"
    android:layout_marginStart="34dp"
    android:layout_marginTop="92dp"
    tools:layout_constraintLeft_creator="1"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    android:layout_marginLeft="34dp" />

<TextView
    android:id="@+id/tv_main"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Your name is"
    tools:layout_constraintTop_creator="1"
    android:layout_marginStart="34dp"
    android:layout_marginTop="33dp"
    tools:layout_constraintLeft_creator="1"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    android:layout_marginLeft="34dp" />

My xml code for NameActivity

 <Button
        android:id="@+id/btn_ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="116dp"
        android:text="ok"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_constraintLeft_creator="1"
        tools:layout_constraintRight_creator="1"
        tools:layout_constraintTop_creator="1" />

    <EditText
        android:id="@+id/et_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="64dp"
        android:layout_marginRight="84dp"
        android:layout_marginTop="31dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Name"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_constraintRight_creator="1"
        tools:layout_constraintTop_creator="1" />
</android.support.constraint.ConstraintLayout>

Upvotes: 1

Views: 270

Answers (4)

anupam_kamble
anupam_kamble

Reputation: 144

You doing setContentView(R.layout.activity_name) in NameActivity and then button = (Button) findViewById(R.id.btn_iputName) which is present in another activity.

Just change

button = (Button) findViewById(R.id.btn_iputName);

to

button = (Button) findViewById(R.id.btn_ok);

it will work for you.

Upvotes: 4

Akash
Akash

Reputation: 697

Wrong ID used for Button

In your second activity i.e., NameActivity.java You need to Replace

button = (Button) findViewById(R.id.btn_iputName);

with

button = (Button) findViewById(R.id.btn_ok);

These changes will resolve the NullPointerException and your app will work properly.

Upvotes: 1

Raghunandan
Raghunandan

Reputation: 133560

You have

setContentView(R.layout.activity_name)

So change this

button = (Button) findViewById(R.id.btn_iputName)

to

button = (Button) findViewById(R.id.btn_ok);

findViewById looks for views with id in the current view hierarchy. So if you have setContentView(R.layout.activity_name) you should look up id in your activity_name.xml.

Upvotes: 3

Akash
Akash

Reputation: 711

In Your NameActivity there is not button of button = (Button) findViewById(R.id.btn_iputName); instead it is there in MainActivity and you are finding in the NameActivity because of which while starting Name activity it is giving NullPointerException.

Upvotes: 2

Related Questions