如何从2个编辑文本中获取值并对其求和，并将其显示为第三个编辑文本而无需任何按钮

Question

如何在不点击按钮的情况下获取两个EditText中的值，求和，并将其显示为第三个EditText？

到目前为止，这是我的代码

public class MainActivity extends Activity {

    int a,b,c;
    EditText fst= (EditText)findViewById(R.id.fstdgt);
    EditText scnd= (EditText)findViewById(R.id.scnddgt);
    EditText thrd= (EditText)findViewById(R.id.thrddgt);
    View v;

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


        a=Integer.parseInt(fst.getText().toString());
        b=Integer.parseInt(scnd.getText().toString());
        c=a+b;
        thrd.setText("" + c);
    }
}

这不起作用。应用程序每次启动时都会崩溃。有没有人有任何建议？

Answer 1

为两个输入编辑框添加textchange侦听器将解决您的问题。这就是我认为应该如何解决你的问题：

int a, b,c;
String input_a = fst.getText().toString();
String input_b = scnd.getText().toString();

fst.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                if (!input_a.isEmpty() && !intput_b.isEmpty()){
                    a = Integer.parseInt(input_a);
                    b= Integer.parseInt(input_b);
                    c = a+b;
                    String answer_value= "" + c;
                    thrd.setText(answer_value);
                } else thrd.setText("");

            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });
//and you need to add TextChangeListener for your "scnd" editText as well.
scnd.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                if (!input_a.isEmpty() && !input_b.isEmpty()){
                    a = Integer.parseInt(input_a);
                    b= Integer.parseInt(input_b);
                    c = a+b;
                    String answer_value= "" + c;
                    thrd.setText(answer_value);
                } else thrd.setText("");

            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });