[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 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，打开如意门