无法实例化活动ComponentInfo... java.lang.NullPointerException。

Question

我在我的应用程序中遇到了“无法实例化活动ComponentInfo”的错误。我已经在AndroidManifest.xml中声明了该Activity，但我仍然收到错误。我不知道是什么原因。有人可以帮忙吗？

谢谢

错误信息：

    FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{br.com.controladoratividades/br.com.controladoratividades.activities.NovaAtividadeActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
at android.app.ActivityThread.access$2300(ActivityThread.java:125)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4627)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.content.ContextWrapper.getResources(ContextWrapper.java:80)
at android.content.Context.getString(Context.java:182)
at br.com.controladoratividades.activities.NovaAtividadeActivity.<init>(NovaAtividadeActivity.java:15)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1429)
at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
... 11 more

我的AndroidManifest.xml文件:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="br.com.controladoratividades"
    android:versionCode="1"
    android:versionName="1.0" >



    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".activities.ControladorAtividadesActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity
            android:name=".activities.NovaAtividadeActivity"
            android:label="@string/nova_atividade" >            
        </activity>

           <activity
            android:name=".activities.PlanejadorActivity"
            android:label="@string/novo_plano" >            
        </activity>         


    </application>

    <uses-sdk android:minSdkVersion="7" />

</manifest>

这个活动：

package br.com.controladoratividades.activities;

import br.com.controladoratividades.R;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class NovaAtividadeActivity extends Activity {

    private String[] DIAS = new String[] {getString(R.string.domingo), 
            getString(R.string.segunda),
            getString(R.string.terca),
            getString(R.string.quarta),
            getString(R.string.quinta),
            getString(R.string.sexta),
            getString(R.string.sabado)};
    protected boolean[] DIAS_SELECIONADOS =  new boolean[ DIAS.length ];

    static final int DIAS_DIALOG_ID = 0;

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

        setContentView(R.layout.nova_atividade);

        Button btAlterarDias = (Button)findViewById(R.id.btSalvarPlano);
        btAlterarDias.setOnClickListener(new AlterarDiasClickHandler());

        for (int i = 1;  i < DIAS_SELECIONADOS.length; i++) {
            DIAS_SELECIONADOS[i] = true;
        }
    }

    public class AlterarDiasClickHandler implements View.OnClickListener{

        @Override
        public void onClick(View v) {
            showDialog(DIAS_DIALOG_ID);

        }       
    }

    @Override
    protected Dialog onCreateDialog( int id ) 
    {
        return 
        new AlertDialog.Builder( this )
            .setTitle( "Planets" )
            .setMultiChoiceItems( 
                    DIAS,
                    DIAS_SELECIONADOS, 
                    new DialogSelectionClickHandler() )
            .setPositiveButton( "OK", new DialogButtonClickHandler() )
            .create();
    }

    public class DialogSelectionClickHandler implements DialogInterface.OnMultiChoiceClickListener
    {
        public void onClick( DialogInterface dialog, int clicked, boolean selected )
        {
            Log.i( "ME", DIAS[ clicked ] + " selected: " + selected );
        }
    }

    public class DialogButtonClickHandler implements DialogInterface.OnClickListener
    {
        public void onClick( DialogInterface dialog, int clicked )
        {
            switch( clicked )
            {
                case DialogInterface.BUTTON_POSITIVE:
                    //printSelectedPlanets();
                    break;
            }
        }
    }
}

- VanessaBR

Answer 1

我们没有代码进行确认，但错误似乎表明您正在尝试从NovaAtividadeActivity的构造函数中使用getString。直到onCreate调用之前，Activity才会被创建，因此您需要将代码从构造函数移动到该函数中。

更新：现在您已经添加了活动的代码，我们可以看到您正在调用getString来初始化成员DIAS，这将发生在类的构造函数中。相反，将DIAS的初始化移到onCreate中。

- K-ballo

---

谢谢，就这样了。我使用了“getString()”来初始化属性，现在我把它放在了“onCreate()”中。 - VanessaBR

谢谢，我将Bundle extras = getIntent().getExtras();用作私有成员。 - shareef