Question

我是Android新手，我正在为Android 2.3.3做一个小游戏但是当我在AVD上运行时，它会自动关闭

代码就像这样

package dam.moviles.adivinaminumero;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.*;
import android.widget.*;
import java.util.*;

public class MainActivity extends ActionBarActivity 
{
    int intentos;
    Random dado=new Random();
    int numAdivinar=dado.nextInt(100)+1;
    Button boton=(Button) findViewById(R.id.button1);
    EditText et=(EditText)findViewById(R.id.cajaNumero);
    TextView tv=(TextView)findViewById(R.id.textView1);
    int numero=Integer.parseInt(et.getText().toString());

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

        et.setOnKeyListener(new android.view.View.OnKeyListener()
        { 
            public boolean onKey(View v, int keyCode, android.view.KeyEvent event)
            {
                if ((event.getAction() == android.view.KeyEvent.ACTION_DOWN) && (keyCode == android.view.KeyEvent.KEYCODE_ENTER)) 
                {
                    if(numero<numAdivinar)
                    {
                        String format=getResources().getString(R.string.mensajeMayor);
                        String cadFinal=String.format(format, numero);
                        tv.setText(cadFinal);
                    }
                    else if(numero>numAdivinar)
                    {
                        String format=getResources().getString(R.string.mensajeMenor);
                        String cadFinal=String.format(format, numero);
                        tv.setText(cadFinal);
                    }
                    else
                    {
                        tv.setText(R.string.acierto);
                    }
                    return true;
                }
                else
                {
                    return false;
                }
            }
        });
    }
}

并抛出NullPointerException

如果我把代码放在OnCreate中，就像这样

package dam.moviles.adivinaminumero;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.*;
import android.widget.*;
import java.util.*;

public class MainActivity extends ActionBarActivity 
{
    int intentos;
    Random dado=new Random();
    int numAdivinar=dado.nextInt(100)+1;
    Button boton;
    EditText et;
    TextView tv;
    int numero;

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

        boton=(Button) findViewById(R.id.button1);
        et=(EditText)findViewById(R.id.cajaNumero);
        tv=(TextView)findViewById(R.id.textView1);
        numero=Integer.parseInt(et.getText().toString());

        et.setOnKeyListener(new android.view.View.OnKeyListener()
        { 
            public boolean onKey(View v, int keyCode, android.view.KeyEvent event)
            {
                if ((event.getAction() == android.view.KeyEvent.ACTION_DOWN) && (keyCode == android.view.KeyEvent.KEYCODE_ENTER)) 
                {
                    if(numero<numAdivinar)
                    {
                        String format=getResources().getString(R.string.mensajeMayor);
                        String cadFinal=String.format(format, numero);
                        tv.setText(cadFinal);
                    }
                    else if(numero>numAdivinar)
                    {
                        String format=getResources().getString(R.string.mensajeMenor);
                        String cadFinal=String.format(format, numero);
                        tv.setText(cadFinal);
                    }
                    else
                    {
                        tv.setText(R.string.acierto);
                    }
                    return true;
                }
                else
                {
                    return false;
                }
            }
        });
    }

使用此LogCat

抛出NumberFormatException

11-18 17:00:22.621: D/AndroidRuntime(595): Shutting down VM
11-18 17:00:22.621: W/dalvikvm(595): threadid=1: thread exiting with uncaught exception (group=0x40015560)
11-18 17:00:22.641: E/AndroidRuntime(595): FATAL EXCEPTION: main
11-18 17:00:22.641: E/AndroidRuntime(595): java.lang.RuntimeException: Unable to start activity ComponentInfo{dam.moviles.adivinaminumero/dam.moviles.adivinaminumero.MainActivity}: java.lang.NumberFormatException: unable to parse '' as integer
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.os.Handler.dispatchMessage(Handler.java:99)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.os.Looper.loop(Looper.java:123)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.ActivityThread.main(ActivityThread.java:3683)
11-18 17:00:22.641: E/AndroidRuntime(595):  at java.lang.reflect.Method.invokeNative(Native Method)
11-18 17:00:22.641: E/AndroidRuntime(595):  at java.lang.reflect.Method.invoke(Method.java:507)
11-18 17:00:22.641: E/AndroidRuntime(595):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-18 17:00:22.641: E/AndroidRuntime(595):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
11-18 17:00:22.641: E/AndroidRuntime(595):  at dalvik.system.NativeStart.main(Native Method)
11-18 17:00:22.641: E/AndroidRuntime(595): Caused by: java.lang.NumberFormatException: unable to parse '' as integer
11-18 17:00:22.641: E/AndroidRuntime(595):  at java.lang.Integer.parseInt(Integer.java:362)
11-18 17:00:22.641: E/AndroidRuntime(595):  at java.lang.Integer.parseInt(Integer.java:332)
11-18 17:00:22.641: E/AndroidRuntime(595):  at dam.moviles.adivinaminumero.MainActivity.onCreate(MainActivity.java:28)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-18 17:00:22.641: E/AndroidRuntime(595):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
11-18 17:00:22.641: E/AndroidRuntime(595):  ... 11 more
11-18 17:00:25.701: I/Process(595): Sending signal. PID: 595 SIG: 9

非常感谢

Answer 1

问题在于：

    numero=Integer.parseInt(et.getText().toString());

您的EditText已空，您无法执行此操作。

Answer 2

第二种方式（抛出NumberFormatException的方式是我在这个答案中提到的方式，因为这是更正确的方法。）

将et声明为final并将numero=Integer.parseInt(et.getText().toString());移至您的onKey方法中。您收到错误的原因是，您的应用首次创建时EditText为空，并且由于您还在首次启动应用时尝试分配numero，因此无需解析。

将numero=Integer.parseInt(et.getText().toString());移至onKey内，您告诉它只在输入内容时解析。

如果用户在EditText中输入了无法从中解析出数字的内容，这仍然会给您一个错误，因此您可以指定只有数字可以输入EditText，或者您可以使用try/catch块包围解析方法。

在您的XML中，使用android:inputType="number"强制只能输入数字。

Answer 3

您的edittext et为null，因为您在活动生命周期方法之外设置了findViewById，并且您尝试将null值转换为int.So change

   Button boton = (Button) findViewById(R.id.button1);
   EditText et = (EditText) findViewById(R.id.cajaNumero);
   TextView tv = (TextView) findViewById(R.id.textView1);
   int numero = Integer.parseInt(et.getText().toString());

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

到

   Button boton;
   EditText et;
   TextView tv;
   int numero = 0;
   @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    boton = (Button) findViewById(R.id.button1);
    et = (EditText) findViewById(R.id.cajaNumero);
    tv = (TextView) findViewById(R.id.textView1);
    if (et.getText().toString().length() != 0) {
        numero = Integer.parseInt(et.getText().toString());
    }

NullPointerException / NumberFormatException（＆＃34;无法实例化活动ComponentInfo＆＃34;）

3 个答案: