.putExtra意向后应用崩溃

Question

I'm trying to send a variable from one activity to another. When I try to test the app on my phone, it crashes and says the app has stopped working.

Code from sending side

if (id==R.id.action_cart){

        Intent good1 = new Intent(MainActivity.this, Scroll.class);

        good1.putExtra("intVariableName", 5);
        startActivity(good1);

        TextView hides = (TextView) findViewById(R.id.textView3);
        hides.setVisibility(View.INVISIBLE);
    }

and code on receiving side

public class Scroll extends AppCompatActivity {
TextView btn = (TextView) findViewById(R.id.text);

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

    Intent mIntent = getIntent();
    int intValue = mIntent.getIntExtra("intVariableName", 0);

    btn.setText(intValue);



}}

If you know what the issue is please let me know. I've spent hours looking for a solution. Thank you

Answer 1

you need to move this TextView btn = (TextView) findViewById(R.id.text); inside oncreate because before oncreate there is no layout attached to Scroll activity and finding textview by using this findViewById(R.id.text) will result in a failure hence crash

public class Scroll extends AppCompatActivity {
    TextView btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scroll);
        btn = (TextView) findViewById(R.id.text)
        //^^^^
        Intent mIntent = getIntent();
        int intValue = mIntent.getIntExtra("intVariableName", 0);
        btn.setText(""+intValue);                
      }
}

Note : Use appropriate naming convention for clarity , like textViewVar for TextView instead of btn and convert your int value to text using ""+value because TextView allow only String to use

Answer 2

I think the problem is in this call: btn.setText(intValue); : string resource ID with value 5 does not exist. Try replacing it with btn.setText(Integer.toString(intValue));

Answer 3

In your activity

public class Scroll extends AppCompatActivity {
TextView btn ;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_scroll);
    btn = (TextView) findViewById(R.id.text); // initialize your button here
    Intent mIntent = getIntent();
    int intValue = mIntent.getIntExtra("intVariableName", 0);

    btn.setText(String.valueOf(intValue));



}}

Answer 4

Try this

    if (id==R.id.action_cart){
         //hide views before moving
           TextView hides = (TextView) findViewById(R.id.textView3);
            hides.setVisibility(View.INVISIBLE);
            Intent good1 = new Intent(MainActivity.this, Scroll.class);
            good1.putExtra("intVariableName", 5);
            startActivity(good1);

        }

and in Recieving activity put this in oncreate

btn = (TextView) findViewById(R.id.text);

Like this

 public class Scroll extends AppCompatActivity {
    TextView btn ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scroll);
        btn = (TextView) findViewById(R.id.text);
        Intent mIntent = getIntent();
        int intValue = mIntent.getIntExtra("intVariableName", 0);
        btn.setText(intValue);



    }}

Answer 5

change a line to: btn.setText(String.valueOf(intValue));

public class Scroll extends AppCompatActivity {
TextView btn = (TextView) findViewById(R.id.text);

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

    Intent mIntent = getIntent();
    int intValue = mIntent.getIntExtra("intVariableName", 0);

    btn.setText(String.valueOf(intValue));
}}

Answer 6

Replace your code by this

public class Scroll extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_scroll);

        TextView btn = (TextView) findViewById(R.id.text);

        Intent mIntent = getIntent();
        int intValue = mIntent.getIntExtra("intVariableName", 0);

        btn.setText(intValue);

    }
}