Null Pointer Exception - Getting EditText Value

问题:

This is my first question on here I will apologize in advance if I didn't ask this question very well. I have looked at my other questions similar to my problem, but I have not found a good solution to satisfy what is going on in my program.

So my problem is I am trying to assign a value to a variable called, num1 from my EditText field called, num1TextField, but I am not having any luck so far.

The segment inside my java file that throws the exception is:

EditText num1Field = (EditText)v.findViewById(R.id.num1TextField);
num1 = num1Field.getText().toString();

I appreciate every contribution to this problem in advance.

---

Here is my fragment_compute.xml file:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="14dp"
    android:text="@string/compute_activity"
    android:textAppearance="?android:attr/textAppearanceLarge" />

<TextView
    android:id="@+id/textView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="44dp"
    android:text="@string/num_1"
    android:textAppearance="?android:attr/textAppearanceMedium" />

<EditText
    android:id="@+id/num1TextField"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView2"
    android:layout_centerHorizontal="true"
    android:ems="10"
    android:inputType="number"
    android:gravity="center" >

    <requestFocus />
</EditText>

<EditText
    android:id="@+id/num2TextField"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/num1TextField"
    android:layout_below="@+id/textView3"
    android:ems="10"
    android:inputType="number"
    android:layout_centerHorizontal="true"
    android:gravity="center" >
</EditText>

<TextView
    android:id="@+id/textView4"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/num2TextField"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="22dp"
    android:text="@string/result"
    android:textAppearance="?android:attr/textAppearanceMedium" />

<TextView
    android:id="@+id/textView3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/num1TextField"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="22dp"
    android:text="@string/num_2"
    android:textAppearance="?android:attr/textAppearanceMedium" />

<TextView
    android:id="@+id/result"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView4"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="22dp" />

<Button
    android:id="@+id/compute_multiply"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignRight="@+id/num2TextField"
    android:layout_below="@+id/result"
    android:layout_marginTop="40dp"
    android:text="@string/multiply" />

<Button
    android:id="@+id/compute_add"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/compute_multiply"
    android:layout_alignBottom="@+id/compute_multiply"
    android:layout_alignLeft="@+id/num2TextField"
    android:text="@string/add" />

</RelativeLayout>

---

Here is my ComputeFragment.java code:

public class ComputeFragment extends Fragment {

    String num1;
    String num2;

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_compute, parent, false);

        // Add Button
        Button addButton = (Button)v.findViewById(R.id.compute_add);
        addButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // ERROR STARTS HERE!
                EditText num1Field = (EditText)v.findViewById(R.id.num1TextField);
                num1 = num1Field.getText().toString(); // Null Pointer Exception is thrown here!

                EditText num2Field = (EditText)v.findViewById(R.id.num2TextField);
                num2 = num2Field.getText().toString();
                // ERROR ENDS HERE!

                Intent i = new Intent(getActivity(), AddActivity.class);
                i.putExtra("x", num1);
                i.putExtra("y", num2);
                startActivityForResult(i,0);
            }
        });

        return v; 
    }
}

---

Thank you all and have a nice day!

回答1:

The parameter v in EditText num1Field = (EditText)v.findViewById(R.id.num1TextField); is your button, not the whole view.

You should declare the variable in onCreateView:

final EditText num1Field = (EditText)v.findViewById(R.id.num1TextField);

And use it to get the value in onClick

num1 = num1Field.getText().toString();

回答2:

The parameter view is the button. If the button is on the same parent as the editTexts you could also do:

View parentView = (View) view.getParent();
EditText num1TextField = (EditText)parentView.findViewById(R.id.num1TextField);

回答3:

Try this code -

@Override
            public void onClick(View view) {
        EditText num1Field = (EditText)v.findViewById(R.id.num1TextField);
          if(num1Field.getText().length() > 0) {
                        num1 = num1Field.getText().toString();
          }
}