E / AndroidRuntime：致命异常：主要

Question

Whenever I try to run my application, an error is showing up in the LogCat. This is my code in MainActivity.java

package com.practice.bludworth.practiceapp;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;


public class MainActivity extends Activity {

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

    EditText ageInput = (EditText) findViewById(R.id.ageReceived);
    int input = Integer.parseInt(ageInput.getText().toString());

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.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();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
   }
}

The error in LogCat says it's:

Caused by: java.lang.NumberFormatException: Invalid int: ""

Very confused as I'm new to programming in general. Thanks

Answer 1

The problem is that you are attempting to parse an Integer on the start of the application, since onCreate is the first method that runs your EditText field has no value.

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MyActivity extends Activity implements View.OnClickListener
{
    private EditText ageInput;

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

        // A button on your xml layout
        Button button = (Button) findViewById(R.id.button);

        // set the on click listener to this class, notice that MyActivity implements View.OnClickListener
        button.setOnClickListener(this);

        // This retrieves the EditText control
        ageInput = (EditText) findViewById(R.id.ageReceived);
    }

    // This method is called when your button is clicked.

    @Override
    public void onClick(View v)
    {


         // Switch cases are equivalent to if statements
         switch (v.getId())
         {
             // if your button was clicked.
             case R.id.button:
                // get the input
                 int input = Integer.parseInt(ageInput.getText().toString());

                 // Print the input to the console
                 Log.d("DEBUG_TAG", String.valueOf(input));
                 break;

         }
    }
}