Android ActionBar随ScorllView上下拖动而透明度渐变效果

转载：http://blog.csdn.net/jan_s/article/details/43772697

我看到越来越多的应用使用这样的效果，如QQ空间5.0的主界面，确实很好看！大概就搜了一下相关的实现方式，发现早就有了相关的方案：

仿QQ空间滚动ActionBar透明度变化Demo

还有我在github上看到就有这样的实现方式，这也是本博文的主要核心内容：

具体请查看：https://github.com/AChep/Header2ActionBar

效果如下：

这是Demo结构：

1.FadingActionBarHelper.java 这个类是处理Actionbar的核心类，处理对scroll事件对actionbar背景色alpha的处理。

 public class FadingActionBarHelper {

     private static final String TAG = "FadingActionBarHelper";

     private int mAlpha = 255;
     private Drawable mDrawable;
     private boolean isAlphaLocked;

     private final ActionBar mActionBar;

     public FadingActionBarHelper(final ActionBar actionBar) {
         mActionBar = actionBar;
     }

     public FadingActionBarHelper(final ActionBar actionBar, final Drawable drawable) {
         mActionBar = actionBar;
         setActionBarBackgroundDrawable(drawable);
     }

     public void setActionBarBackgroundDrawable(Drawable drawable) {
         setActionBarBackgroundDrawable(drawable, true);
     }

     @TargetApi(Build.VERSION_CODES.KITKAT)
     public void setActionBarBackgroundDrawable(Drawable drawable, boolean mutate) {
         mDrawable = mutate ? drawable.mutate() : drawable;
         mActionBar.setBackgroundDrawable(mDrawable);
         if (mAlpha == 255) {
             if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)
                 mAlpha = mDrawable.getAlpha();
         } else {
             setActionBarAlpha(mAlpha);
         }
     }

     /**
      * An {@link android.app.ActionBar} background drawable.
      *
      * @see #setActionBarBackgroundDrawable(android.graphics.drawable.Drawable)
      * @see #setActionBarAlpha(int)
      */
     public Drawable getActionBarBackgroundDrawable() {
         return mDrawable;
     }

     /**
      * Please use this method for global changes only!
      * This is helpful when you need to provide something like
      * Navigation drawer: lock ActionBar and set
      * {@link android.graphics.drawable.Drawable#setAlpha(int)}
      * to {@link #getActionBarBackgroundDrawable()} directly.
      *
      * @param alpha a value from 0 to 255
      * @see #getActionBarBackgroundDrawable()
      * @see #getActionBarAlpha()
      */
     public void setActionBarAlpha(int alpha) {
         if (mDrawable == null) {
             Log.w(TAG, "Set action bar background before setting the alpha level!");
             return;
         }
         if (!isAlphaLocked) {
             mDrawable.setAlpha(alpha);
             View view = mActionBar.getCustomView();
             if(view!=null){
                 //这里是对自定义actionbar背景的处理，我这边就草草了事了
                 if(alpha>=55){
                     view.findViewById(R.id.search_button).setBackgroundResource(R.drawable.search);
                     view.findViewById(R.id.refresh_button).setBackgroundResource(R.drawable.refresh);
                 }else{
                     view.findViewById(R.id.search_button).setBackgroundResource(R.drawable.skin_nav_icon_l_search_rev);
                     view.findViewById(R.id.refresh_button).setBackgroundResource(R.drawable.skin_nav_icon_r_refresh_rev);
                 }
                 Log.i(TAG, "search_button.alpha=>"+alpha);
             }
         }
         mAlpha = alpha;
     }

     public int getActionBarAlpha() {
         return mAlpha;
     }

     /**
      * When ActionBar's alpha is locked {@link #setActionBarAlpha(int)}
      * won't change drawable\'s alpha (but will change {@link #getActionBarAlpha()} level)
      *
      * @param lock
      */
     public void setActionBarAlphaLocked(boolean lock) {

         // Update alpha level on unlock
         if (isAlphaLocked != (isAlphaLocked = lock) && !isAlphaLocked) {
             setActionBarAlpha(mAlpha);
         }
     }

     public boolean isActionBarAlphaLocked() {
         return isAlphaLocked;
     }
 }

2.其他的组件类我这不copy了，有兴趣的朋友自行下载github上的项目吧o(∩_∩)o。

 public class NotifyingScrollView extends ScrollView {
     // Edge-effects don't mix well with the translucent action bar in Android 2.X
     private boolean mDisableEdgeEffects = true;

     /**
      * @author Cyril Mottier
      */
     public interface OnScrollChangedListener {
         void onScrollChanged(ScrollView who, int l, int t, int oldl, int oldt);
     }

     private OnScrollChangedListener mOnScrollChangedListener;

     public NotifyingScrollView(Context context) {
         super(context);
     }

     public NotifyingScrollView(Context context, AttributeSet attrs) {
         super(context, attrs);
     }

     public NotifyingScrollView(Context context, AttributeSet attrs, int defStyle) {
         super(context, attrs, defStyle);
     }

     @Override
     protected void onScrollChanged(int l, int t, int oldl, int oldt) {
         super.onScrollChanged(l, t, oldl, oldt);
         if (mOnScrollChangedListener != null) {
             mOnScrollChangedListener.onScrollChanged(this, l, t, oldl, oldt);
         }
     }

     public void setOnScrollChangedListener(OnScrollChangedListener listener) {
         mOnScrollChangedListener = listener;
     }

     @Override
     protected float getTopFadingEdgeStrength() {
         // http://stackoverflow.com/a/6894270/244576
         if (mDisableEdgeEffects && Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
             return 0.0f;
         }
         return super.getTopFadingEdgeStrength();
     }

     @Override
     protected float getBottomFadingEdgeStrength() {
         // http://stackoverflow.com/a/6894270/244576
         if (mDisableEdgeEffects && Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
             return 0.0f;
         }
         return super.getBottomFadingEdgeStrength();
     }
 }

3.对于普通的java程序员来说，你可以不知道怎么个原理，但是你一定要知道怎么运用它，如何运用到我们的实际项目中并且改造它，这是demo的主界面，用起来就几行代码，是不是很叼？

 public class MainActivity extends Activity {

     private FadingActionBarHelper mFadingActionBarHelper;
     private ActionBar mActionBar;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         mActionBar = getActionBar();
         //使用自定义的布局的ActionBar
         mActionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
         mActionBar.setCustomView(R.layout.my_actionbar);
         //定义白色为Actionbar的背景色
         mFadingActionBarHelper = new FadingActionBarHelper(getActionBar(),
                 getResources().getDrawable(R.drawable.actionbar_bg));

         if (savedInstanceState == null) {
             getFragmentManager().beginTransaction()
                     .add(R.id.container, new ListViewFragment())
                     .commit();
         }
     }


     @Override
     public boolean onCreateOptionsMenu(Menu menu) {

         // Inflate the menu; this adds items to the action bar if it is present.
         //菜单页面碍于效果，即被隐藏
 //        getMenuInflater().inflate(R.menu.main, menu);
         return true;
     }

     @Override
     public boolean onOptionsItemSelected(MenuItem item) {
         // Handle action bar item clicks here. The action bar will
         // automatically handle clicks on the Home/Up button, so long
         // as you specify a parent activity in AndroidManifest.xml.
         return super.onOptionsItemSelected(item);
     }

     //这段代码可不要忘了
     public FadingActionBarHelper getFadingActionBarHelper() {
         return mFadingActionBarHelper;
     }
 }

贴了主要的代码，其实这个实现方式还是有点复杂的，我想应该还有更简洁的方式吧，有的话请留言分享！分享代码是技术圈进步的一种有效方式哦！

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最后是Demo的下载链接，有兴趣的请自行下载：http://download.csdn.net/download/sunjundelove/8444749