android 轻松搞定标题随scrollview滑动变色

来源：互联网发布：slack软件编辑：程序博客网时间：2024/04/30 03:57

要实现某个view的背景透明度跟随scrollview滑动而改变需要重新scrollview的onOverScrolled方法，该方法随着滑动变化（包括手指滑动、手指移开惯性滑动）而响应，所以最适合做变色处理。

step1:设定布局

由于我们要实现的是滑动时标题的背景透明度改变，固定顶部的标题view不能在srcollview里面跟随滑动，所以需要这样布局:

    <FrameLayout        android:layout_width="match_parent"        android:layout_height="match_parent">        <com.****.ScrollChangeScrollView            android:id="@+id/scrollView"            android:layout_width="match_parent"            android:layout_height="match_parent"            android:fillViewport="true">            <LinearLayout                android:layout_width="match_parent"                android:layout_height="match_parent"                android:orientation="vertical">                    <TextView                        android:layout_width="0dp"                        android:layout_height="wrap_content"                        android:layout_weight="1"                        android:drawablePadding="5dp"                        android:drawableTop="@drawable/dicovery_vintner_icon_wine"                        android:gravity="center"                        android:text="葡萄酒"                        android:textColor="@color/hometitlebg" />            </LinearLayout>        </com.***.ScrollChangeScrollView>        <Button            android:id="@+id/btn_back"            android:layout_width="match_parent"            android:layout_height="35dp"            android:layout_centerVertical="true"            android:background="@null"            android:drawableLeft="@drawable/icon_back"            android:padding="10dp" />    </FrameLayout>

step2:添加需要用到的方法

滑动时，某个view要变色，重新scrollview后，添加方法让其知道该view需要变色

    private View mTitleView;    /**     * 变色标题view     * @param view     */    public void setupTitleView (View view) {        this.mTitleView = view;    }

滑动时变色需要参考scrollview里面的某个子view的滑动高度，如果该子view上划完全划出屏幕，则标题view背景透明为0：

    private View mByWhichView;    /**     * 跟随的view     * @param view     */    public void setupByWhichView(View view) {        mByWhichView = view;    }

再添加一个设置，如果不要背景透明度渐变：

    private boolean shouldSlowlyChange;    public void setShouldSlowlyChange(boolean slowlyChange) {        this.shouldSlowlyChange = slowlyChange;    }

step3:代码实现

** * 滑动时标题变色view * Created by george.yang on 16/2/21. */public class ScrollChangeScrollView extends ScrollView {    private View mByWhichView;    private View mTitleView;    private boolean shouldSlowlyChange = true;    public ScrollChangeScrollView(Context context) {        super(context);    }    public ScrollChangeScrollView(Context context, AttributeSet attrs) {        super(context, attrs);    }    public ScrollChangeScrollView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);    }    @TargetApi(Build.VERSION_CODES.LOLLIPOP)    public ScrollChangeScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {        super(context, attrs, defStyleAttr, defStyleRes);    }    @Override    public void scrollTo(int x, int y) {        //这是为了修复noScrllListView嵌套在srcollview时就自动滑动到noscrolllistview的顶部的bug，不影响使用        if (x == 0 && y == 0 || y <= 0) {            super.scrollTo(x, y);        }    }    public void setListener(OnScrollListener listener){        this.mListener = listener;    }    public void setShouldSlowlyChange(boolean slowlyChange) {        this.shouldSlowlyChange = slowlyChange;    }    /**     * 设置透明度渐变的标题view     * @param view     */    public void setupTitleView (View view) {        this.mTitleView = view;    }    /**     * 跟随的view     * @param view     */    public void setupByWhichView(View view) {        mByWhichView = view;    }    @Override    protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX,                                  boolean clampedY) {        super.onOverScrolled(scrollX, scrollY, clampedX, clampedY);        if (scrollY >= mByWhichView.getTop() + mByWhichView.getMeasuredHeight()) {            mTitleView.setBackgroundColor(Color.BLACK);        } else if (scrollY>=0) {            if (!shouldSlowlyChange) {                mTitleView.setBackgroundColor(Color.TRANSPARENT);            } else {                float persent = scrollY * 1f / (mByWhichView.getTop() + mByWhichView.getMeasuredHeight());                int alpha = (int) (255 * persent);                int color = Color.argb(alpha,0,0,0);                mTitleView.setBackgroundColor(color);            }        }        if (mListener!=null) {            mListener.onScroll(scrollX, scrollY);        }    }}

效果如下:

滑动前

滑动变色中

参考的view超出屏幕后

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