java - 简单应用程序的问题

Question

我是编码新手，我试图制作一个简单的应用程序，从 2 个变量中进行减法，但是当我单击按钮进行计算时，应用程序崩溃了......有人可以帮助我找到代码中的问题吗？ (Android Studio)

代码如下:

package apps.ste.resto;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.TextView;

import static apps.ste.resto.R.id.risultato;

public class MainActivity extends AppCompatActivity {

TextView importo;
TextView conto;
TextView risultato;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    TextView risultato = (TextView) findViewById(R.id.textView);
    TextView importo = (TextView) findViewById(R.id.editText);
    TextView conto = (TextView) findViewById(R.id.editText2);
    Button bottone = (Button) findViewById(R.id.button);
    bottone.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            result();
        }
    });
}

public void result(){
    float result = Float.parseFloat(importo.getText().toString()) - Float.parseFloat(conto.getText().toString());
    risultato.setText(Float.toString(result));
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

Answer 1

我认为您得到的 getText() 值为空值..

所以你可以尝试这个:

public void result(){

   boolean digitsOnly1 = TextUtils.isDigitsOnly(importo.getText()+"");
   boolean digitsOnly2 = TextUtils.isDigitsOnly(conto.getText()+"");

   if(digitsOnly1 && digitsOnly2){
        float result = Float.parseFloat(importo.getText().toString()) - Float.parseFloat(conto.getText().toString());
        risultato.setText(result+""));
   }else{
        risultato.setText("Please provide inputs");
   }

}