無法實例化活動ComponentInfo，android？

Question

我想在我的應用程序中實現ObservableScrollView。但我得到這個例外，下面當我運行

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.admin.obserscroll/com.example.admin.obserscroll.MainActivity}: java.lang.InstantiationException: can't instantiate class com.example.admin.obserscroll.MainActivity 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2163) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286) 
     at android.app.ActivityThread.access$800(ActivityThread.java:145) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1243) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:136) 
     at android.app.ActivityThread.main(ActivityThread.java:5127) 
     at java.lang.reflect.Method.invokeNative(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:515) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:641) 
     at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.InstantiationException: can't instantiate class com.example.admin.obserscroll.MainActivity 
     at java.lang.Class.newInstanceImpl(Native Method) 
     at java.lang.Class.newInstance(Class.java:1208) 
     at android.app.Instrumentation.newActivity(Instrumentation.java:1061) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2154) 

這是我的活動類

public abstract class MainActivity<S extends Scrollable> extends ActionBarActivity implements ObservableScrollViewCallbacks { 
private Toolbar mToolbar; 
private S mScrollable; 
private static final int NUM_OF_ITEMS_FEW = 3; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    mToolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(mToolbar); 

    mScrollable = createScrollable(); 
    mScrollable.setScrollViewCallbacks(this); 
    ObservableRecyclerView recyclerView = (ObservableRecyclerView) findViewById(R.id.scrollable); 
    recyclerView.setLayoutManager(new LinearLayoutManager(this)); 
    recyclerView.setHasFixedSize(true); 
    recyclerView.setAdapter(new SimpleRecyclerAdapter(this, getDummyData(NUM_OF_ITEMS_FEW))); 
} 




public static ArrayList<String> getDummyData(int num) { 
    ArrayList<String> items = new ArrayList<String>(); 
    for (int i = 1; i <= num; i++) { 
     items.add("Item " + i); 
    } 
    return items; 
} 

protected abstract S createScrollable(); 

@Override 
public void onScrollChanged(int scrollY, boolean firstScroll, boolean dragging) { 
} 

@Override 
public void onDownMotionEvent() { 
} 

@Override 
public void onUpOrCancelMotionEvent(ScrollState scrollState) { 
    Log.e("DEBUG", "onUpOrCancelMotionEvent: " + scrollState); 
    if (scrollState == ScrollState.UP) { 
     if (toolbarIsShown()) { 
      hideToolbar(); 
     } 
    } else if (scrollState == ScrollState.DOWN) { 
     if (toolbarIsHidden()) { 
      showToolbar(); 
     } 
    } 
} 

private boolean toolbarIsShown() { 
    return ViewHelper.getTranslationY(mToolbar) == 0; 
} 

private boolean toolbarIsHidden() { 
    return ViewHelper.getTranslationY(mToolbar) == -mToolbar.getHeight(); 
} 

private void showToolbar() { 
    moveToolbar(0); 
} 

private void hideToolbar() { 
    moveToolbar(-mToolbar.getHeight()); 
} 

private void moveToolbar(float toTranslationY) { 
    if (ViewHelper.getTranslationY(mToolbar) == toTranslationY) { 
     return; 
    } 
    ValueAnimator animator = ValueAnimator.ofFloat(ViewHelper.getTranslationY(mToolbar), toTranslationY).setDuration(200); 
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { 
     @Override 
     public void onAnimationUpdate(ValueAnimator animation) { 
      float translationY = (float) animation.getAnimatedValue(); 
      ViewHelper.setTranslationY(mToolbar, translationY); 
      ViewHelper.setTranslationY((View) mScrollable, translationY); 
      FrameLayout.LayoutParams lp = (FrameLayout.LayoutParams) ((View) mScrollable).getLayoutParams(); 
      lp.height = (int) -translationY + getScreenHeight() - lp.topMargin; 
      ((View) mScrollable).requestLayout(); 
     } 
    }); 
    animator.start(); 
} 
protected int getScreenHeight() { 
    return findViewById(android.R.id.content).getHeight(); 
}} 

活動XML

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:id="@+id/content" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
android:paddingBottom="@dimen/activity_vertical_margin" 
tools:context=".MainActivity"> 

<android.support.v7.widget.Toolbar 
    android:id="@+id/toolbar" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:background="?attr/colorPrimary" 
    android:minHeight="?attr/actionBarSize" 
    app:popupTheme="@style/Theme.AppCompat.Light.DarkActionBar" 
    app:theme="@style/Toolbar" /> 

<com.github.ksoichiro.android.observablescrollview.ObservableRecyclerView 
    android:id="@+id/scrollable" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:layout_marginTop="?attr/actionBarSize" /> 

Answer 1

爲什麼你是否讓你的活動abstract？ Java不允許你創建它的一個實例，所以要麼刪除關鍵字要麼創建一些實現。