应用程序没有启动（Android运行时：致命的例外：主）

Question

请帮我找出代码的问题。首先，应用程序按预期工作，但当屏幕方向从纵向更改为横向时，应用程序正在破坏，这就是为什么我决定添加“onSaveInstanceState（Bundle outState）”和“onRestoreInstanceState（Bundle savedInstanceState）”的原因，我在Java中是个新手，但我试着自己解决了四天，没有任何实际结果。

以下是我的Java代码和日志：

package com.example.android.dartscounter;

  import android.os.Bundle;
  import android.support.v7.app.AppCompatActivity;
  import android.view.View;
  import android.widget.NumberPicker;
  import android.widget.TextView;


  public class MainActivity extends AppCompatActivity {
  int scorePlayerOne = 0;
  int scorePlayerTwo = 0;
  NumberPicker noPicker;
  NumberPicker niPicker;
  int currentValue = 0;
  int currentValue2 = 0;
  static final String STATE_SCORE_ONE = "myInt";
  static final String STATE_SCORE_TWO = "myIntt";


  @Override
  protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  noPicker.setMinValue(0);
  noPicker.setMaxValue(20);
  noPicker.setWrapSelectorWheel(true);
  noPicker = (NumberPicker) findViewById(R.id.pickerOne);

  niPicker.setMinValue(0);
  niPicker.setMaxValue(20);
  niPicker.setWrapSelectorWheel(true);
  niPicker = (NumberPicker) findViewById(R.id.pickerTwo);

  }


  /**
  * Displays the given score for Player1.
  */
  public void displayForPlayerOne(int score) {
  TextView scoreView = (TextView) findViewById(R.id.playerOneScore);
  scoreView.setText(String.valueOf(score));

  }

  public void addToPlayerOne(View v) {
  currentValue = noPicker.getValue();
  scorePlayerOne = scorePlayerOne + currentValue;
  displayForPlayerOne(scorePlayerOne);

  }

  public void multiplyTwoPlayerOne(View v) {
  currentValue = noPicker.getValue();
  scorePlayerOne = scorePlayerOne + currentValue * 2;
  displayForPlayerOne(scorePlayerOne);
  }

  public void multiplyThreePlayerOne(View v) {
  currentValue = noPicker.getValue();
  scorePlayerOne = scorePlayerOne + currentValue * 3;
  displayForPlayerOne(scorePlayerOne);

  }

  /**
  * Displays the given score for Player2.
  */

  public void displayForPlayerTwo(int score) {
  TextView scoreView = (TextView) findViewById(R.id.playerTwoScore);
  scoreView.setText(String.valueOf(score));

  }

  public void addToPlayerTwo(View v) {
  currentValue2 = niPicker.getValue();
  scorePlayerTwo = scorePlayerTwo + currentValue2;
  displayForPlayerTwo(scorePlayerTwo);

  }

  public void multiplyTwoPlayerTwo(View v) {
  currentValue2 = niPicker.getValue();
  scorePlayerTwo = scorePlayerTwo + currentValue2 * 2;
  displayForPlayerTwo(scorePlayerTwo);
  }

  public void multiplyThreePlayerTwo(View v) {
  currentValue2 = niPicker.getValue();
  scorePlayerTwo = scorePlayerTwo + currentValue2 * 3;
  displayForPlayerTwo(scorePlayerTwo);

  }

  public void reset(View v) {
  scorePlayerOne = 0;
  scorePlayerTwo = 0;
  displayForPlayerTwo(scorePlayerTwo);
  displayForPlayerOne(scorePlayerOne);


  }

  @Override
  public void onSaveInstanceState(Bundle outState) {
  setContentView(R.layout.activity_main);
  super.onSaveInstanceState(outState);

  outState.putInt(STATE_SCORE_ONE, scorePlayerOne);
  outState.putInt(STATE_SCORE_TWO, scorePlayerTwo);


  }

  @Override
  public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  setContentView(R.layout.activity_main);
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.
  scorePlayerOne = savedInstanceState.getInt(STATE_SCORE_ONE);
  scorePlayerTwo = savedInstanceState.getInt(STATE_SCORE_TWO);
  }


  }

xml:

<?xml version="1.0" encoding="utf-8"?>
  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="#f5f5f5"
  android:orientation="vertical"
  android:theme="@android:style/Theme.Material"
  tools:context="com.example.android.dartscounter.MainActivity"
  tools:ignore="NewApi">


  <LinearLayout
  android:id="@+id/linearLayout"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="horizontal">


  <LinearLayout
  android:layout_width="0dp"
  android:layout_height="wrap_content"
  android:layout_weight="0.5"
  android:orientation="vertical">

  <TextView
  android:id="@+id/player_1"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:fontFamily="casual"
  android:gravity="center_horizontal"
  android:padding="16dp"
  android:text="Player 1"
  android:textColor="#616161"
  android:textSize="14sp" />

  <TextView
  android:id="@+id/playerOneScore"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginBottom="24dp"
  android:fontFamily="casual"
  android:gravity="center_horizontal"
  android:text="0"
  android:textColor="#000000"
  android:textSize="56sp" />

  <NumberPicker
  android:id="@+id/pickerOne"
  android:layout_width="match_parent"
  android:layout_height="50dp"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:clickable="true"
  android:descendantFocusability="blocksDescendants"
  android:scrollbarAlwaysDrawVerticalTrack="true"
  android:soundEffectsEnabled="true"
  android:theme="@style/Base.V22.Theme.AppCompat.Light" />

  <Button
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginBottom="8dp"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:onClick="addToPlayerOne"
  android:text="add" />

  <Button
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginBottom="8dp"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:onClick="multiplyTwoPlayerOne"
  android:text="x 2" />

  <Button
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:onClick="multiplyThreePlayerOne"
  android:text="x 3" />
  </LinearLayout>

  <View
  android:layout_width="0.2dp"
  android:layout_height="match_parent"
  android:layout_marginTop="16dp"
  android:background="#212121"
  android:id="@+id/view_view"/>

  <LinearLayout
  android:layout_width="0dp"
  android:layout_height="wrap_content"
  android:layout_weight="0.5"
  android:orientation="vertical">

  <TextView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:fontFamily="casual"
  android:gravity="center_horizontal"
  android:padding="16dp"
  android:text="Player 2"
  android:textColor="#616161"
  android:textSize="14sp"
  android:id="@+id/player_2"/>

  <TextView
  android:id="@+id/playerTwoScore"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginBottom="24dp"
  android:fontFamily="casual"
  android:gravity="center_horizontal"
  android:text="0"
  android:textColor="#000000"
  android:textSize="56sp" />

  <NumberPicker
  android:id="@+id/pickerTwo"
  android:layout_width="match_parent"
  android:layout_height="50dp"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:descendantFocusability="blocksDescendants"
  android:isScrollContainer="true"
  android:theme="@style/Base.V22.Theme.AppCompat.Light" />

  <Button
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginBottom="8dp"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:onClick="addToPlayerTwo"
  android:text="add" />

  <Button
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginBottom="8dp"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:onClick="multiplyTwoPlayerTwo"
  android:text="x 2" />

  <Button
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginLeft="24dp"
  android:layout_marginRight="24dp"
  android:onClick="multiplyThreePlayerTwo"
  android:text="x 3" />
  </LinearLayout>


  </LinearLayout>

  <ImageButton
  android:id="@+id/imageButton"
  style="@android:style/Widget.ImageButton"
  android:layout_width="70dp"
  android:layout_height="70dp"
  android:layout_below="@+id/linearLayout"
  android:layout_centerHorizontal="true"
  android:layout_marginTop="30dp"
  android:onClick="reset"
  android:scaleType="centerCrop"
  android:visibility="visible"
  app:srcCompat="@drawable/vector" />

  <TextView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@id/imageButton"
  android:layout_centerHorizontal="true"
  android:text="Reset"
  android:textColor="#424242" />


  </RelativeLayout>

错误日志：

                                                 --------- beginning of crash
03-23 20:55:23.365 2528-2528/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                 Process: com.example.android.dartscounter, PID: 2528
                                                 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.dartscounter/com.example.android.dartscounter.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.android.dartscounter.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.android.dartscounter-1/base.apk"],nativeLibraryDirectories=[/data/app/com.example.android.dartscounter-1/lib/x86, /vendor/lib, /system/lib]]
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                     at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)
                                                     at android.os.Looper.loop(Looper.java:148)
                                                     at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                  Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.android.dartscounter.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.android.dartscounter-1/base.apk"],nativeLibraryDirectories=[/data/app/com.example.android.dartscounter-1/lib/x86, /vendor/lib, /system/lib]]
                                                     at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
                                                     at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
                                                     at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
                                                     at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                     at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                     at android.os.Looper.loop(Looper.java:148) 
                                                     at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                     at java.lang.reflect.Method.invoke(Native Method) 
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
                                                    Suppressed: java.lang.ClassNotFoundException: com.example.android.dartscounter.MainActivity
                                                     at java.lang.Class.classForName(Native Method)
                                                     at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
                                                     at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
                                                     at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
                                                            ... 12 more
                                                  Caused by: java.lang.NoClassDefFoundError: Class not found using the boot class loader; no stack trace available
03-23 20:55:29.709 2528-2528/com.example.android.dartscounter I/Process: Sending signal. PID: 2528 SIG: 9

AndroidManifest：

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.android.dartscounter" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme" >
        <activity android:name=".MainActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

Answer 1

ClassNotFoundException通常是由于活动未在Android清单中声明而导致的。使用以下代码将活动添加到清单：

<activity android:name="YourActivityName"/>