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

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 unlockif (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.Xprivate 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);}@Overrideprotected 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;}@Overrideprotected float getTopFadingEdgeStrength() {// if (mDisableEdgeEffects && Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {return 0.0f;}return super.getTopFadingEdgeStrength();}@Overrideprotected float getBottomFadingEdgeStrength() {// if (mDisableEdgeEffects && Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {return 0.0f;}return super.getBottomFadingEdgeStrength();}}都属于昨天。哪怕那山再青，那水再秀，