爲什麼我的應用程序在打開時立即崩潰？

Question

我正在創建一個2人遊戲反應應用程序，試圖學習一些關於Java/Android的新東西（比如線程），並且意識到每當我嘗試打開該應用程序時，它就會進入黑屏並立即說出「你的APP沒有迴應」（或類似的東西），儘管我幾乎沒有編碼任何東西。

我的MainActivity類別：

public class MainActivity extends Activity implements View.OnClickListener { 

Button player1, player2; 
Random random; 
Double color; 
Thread timer; 
long x, elapsed; 

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

private void game() { 
    color = random.nextDouble(); 
    x = System.currentTimeMillis(); 
} 

private void initializeVar() { 
    Button player1 = (Button) findViewById(R.id.bPlayer1); 
    Button player2 = (Button) findViewById(R.id.bPlayer2); 
    player1.setOnClickListener(this); 
    player2.setOnClickListener(this); 
    player1.getBackground().setColorFilter(0xFFFF0000, 
      PorterDuff.Mode.MULTIPLY); 
    player2.getBackground().setColorFilter(0xFFFF0000, 
      PorterDuff.Mode.MULTIPLY); 
} 

@Override 
public void onClick(View v) { 
    switch (v.getId()) { 

    case R.id.bPlayer1: 
     elapsed = System.currentTimeMillis(); 
     elapsed = elapsed - x; 
     if (elapsed < 10) { 
     } else { 
     } 
     break; 

    case R.id.bPlayer2: 
     elapsed = System.currentTimeMillis(); 
     elapsed = elapsed - x; 
     if (elapsed < 10) { 

     } else { 

     } 
     break; 
    } 
} 

} 

活動XML：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
tools:context=".MainActivity" > 

<Button 
    android:id="@+id/bPlayer1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentTop="true" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="100dp" 
    android:src="@drawable/ic_launcher" /> 

<Button 
    android:id="@+id/bPlayer2" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentBottom="true" 
    android:layout_centerHorizontal="true" 
    android:layout_marginBottom="100dp" 
    android:src="@drawable/ic_launcher" /> 

</RelativeLayout> 

我的清單：

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

<uses-sdk 
    android:minSdkVersion="8" 
    android:targetSdkVersion="17" /> 

<application 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" > 
    <activity 
     android:name="com.meteorfiber.reaction.MainActivity" 
     android:label="@string/app_name" 
     android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

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

</manifest> 

MY logcat的：

02-20 20:27:54.803: E/AndroidRuntime(1747): FATAL EXCEPTION: main 
02-20 20:27:54.803: E/AndroidRuntime(1747): java.lang.RuntimeException: Unable to start  activity ComponentInfo{com.meteorfiber.reaction/com.meteorfiber.reaction.MainActivity}: java.lang.NullPointerException 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.ActivityThread.access$600(ActivityThread.java:123) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.os.Handler.dispatchMessage(Handler.java:99) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.os.Looper.loop(Looper.java:137) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.ActivityThread.main(ActivityThread.java:4424) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at java.lang.reflect.Method.invokeNative(Native Method) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at java.lang.reflect.Method.invoke(Method.java:511) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at dalvik.system.NativeStart.main(Native Method) 
02-20 20:27:54.803: E/AndroidRuntime(1747): Caused by: java.lang.NullPointerException 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at com.meteorfiber.reaction.MainActivity.game(MainActivity.java:28) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at com.meteorfiber.reaction.MainActivity.onCreate(MainActivity.java:24) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.Activity.performCreate(Activity.java:4465) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 
02-20 20:27:54.803: E/AndroidRuntime(1747):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 

Answer 1

random對象是null。初始化它！

private void initializeVar() 
{ 

    random = new Random(); // HERE! 
    Button player1 = (Button) findViewById(R.id.bPlayer1); 
    Button player2 = (Button) findViewById(R.id.bPlayer2); 
    player1.setOnClickListener(this); 
    player2.setOnClickListener(this); 
    player1.getBackground().setColorFilter(0xFFFF0000, 
      PorterDuff.Mode.MULTIPLY); 
    player2.getBackground().setColorFilter(0xFFFF0000, 
      PorterDuff.Mode.MULTIPLY); 
} 

Answer 2

看起來你在使用它之前沒有初始化變量'random'。

Random random = new Random(); 

Answer 3

你應該初始化隨機對象

Random random = new Random;