滚动时的Imageview视差

Question

我在滚动或列表视图视差时看到了许多示例性视差背景,但我无法找到一个清晰的示例,当您在活动中滚动时如何对图像实现视差效果.

可以在Airbnb应用程序中找到示例实现.当您向下滚动时,您可以看到更多图像的底部,当您向上滚动时,您可以看到更多图像的顶部.

关于如何创造这种效果的任何提示和技巧？

Answer 1

有几个库可以产生视差效果,如果它们对您的特定情况有用,则取决于您的应用,例如:

• ParallaxScroll
• Paralloid

谷歌是你的朋友朋友;)如果这些都不适合你的需求那么你必须创建一个自定义,ScrollView但这是一个更长的故事,首先尝试并发布你的结果.

编辑

如果这些都不符合您的要求那么这就是您必须做的事情:

首先,创建一个自定义,ScrollView以便您可以收听滚动更改.

public class ObservableScrollView extends ScrollView {

    public interface OnScrollChangedListener {
        public void onScrollChanged(int deltaX, int deltaY);
    }

    private OnScrollChangedListener mOnScrollChangedListener;

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

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

    public ObservableScrollView(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(l - oldl, t - oldt);
        }
    }

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

显然你需要在你的布局中使用它而不是默认值ScrollView:

<your.app.package.ObservableScrollView
        android:id="@+id/scroll_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

此外,您需要将ImageView包装在容器中以使视差工作:

<FrameLayout
    android:id="@+id/img_container"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <ImageView
        android:id="@+id/img"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop" />
</FrameLayout>

最后设置你Activity作为全新的倾听者ObservableScrollView,让视差开始:

public class MyActivity extends Activity implements ObservableScrollView.OnScrollChangedListener {
    private ObservableScrollView mScrollView;
    private View imgContainer;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        // Init your layout and set your listener
        mScrollView = (ObservableScrollView)findViewById(R.id.scroll_view);
        mScrollView.setOnScrollChangedListener(this);
        // Store the reference of your image container
        imgContainer = findViewById(R.id.img_container);
    }

     @Override
    public void onScrollChanged(int deltaX, int deltaY) {
        int scrollY = mScrollView.getScrollY();
        // Add parallax effect
        imgContainer.setTranslationY(scrollY * 0.5f);
    }
}

您可以根据所需的视差量修改0.5值.

编辑

如果您的ImageView位于活动的顶部,则上述答案可以正常工作.我在下面发布一些代码来添加功能,让ImageView在我成功运作的活动布局中的任何地方.这些是通用计算(可能有一些错误),稍加调整就可以让它适用于您自己的情况.

对于此示例,我具有图像容器200dp和图像240dp的固定高度.主要目的是当图像容器位于屏幕中间时没有视差效果,并且当用户向上或向下滚动以应用效果时.因此,当图像容器越来越接近屏幕的顶部或越接近屏幕的底部时,将应用越多的视差效果.通过阅读它们有点难以理解以下计算,因此尝试用纸上的实数做一个例子.

public class MyActivity extends Activity implements ObservableScrollView.OnScrollChangedListener {
    private ObservableScrollView mScrollView;
    private View imgContainer;
    private ImageView mImageView;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        // Init your layout and set your listener
        mScrollView = (ObservableScrollView)findViewById(R.id.scroll_view);
        mScrollView.setOnScrollChangedListener(this);
        // Store the reference of your image container
        imgContainer = findViewById(R.id.img_container);
        // Store the reference of your image
        mImageView =  findViewById(R.id.img);
    }

     @Override
    public void onScrollChanged(int deltaX, int deltaY) {
        // Get scroll view screen bound
        Rect scrollBounds = new Rect();
        mScrollView.getHitRect(scrollBounds);

        // Check if image container is visible in the screen
        // so to apply the translation only when the container is visible to the user
        if (imgContainer.getLocalVisibleRect(scrollBounds)) {
            Display display = getWindowManager().getDefaultDisplay();
            DisplayMetrics outMetrics = new DisplayMetrics ();
            display.getMetrics(outMetrics);
            // Get screen density
            float density  = getResources().getDisplayMetrics().density;

            // Get screen height in pixels            
            float dpHeight = outMetrics.heightPixels / density;
            int screen_height_pixels = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dpHeight, getResources().getDisplayMetrics());
            int half_screen_height = screen_height_pixels/2;

            // Get image container height in pixels
            int container_height_pixels = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 200, getResources().getDisplayMetrics());

            // Get the location that consider a vertical center for the image (where the translation should be zero)
            int center = half_screen_height - (container_height_pixels/2);

            // get the location (x,y) of the image container in pixels
            int[] loc_screen = {0,0};
            imgContainer.getLocationOnScreen(loc_screen);

            // trying to transform the current image container location into percentage
            // so when the image container is exaclty in the middle of the screen percentage should be zero
            // and as the image container getting closer to the edges of the screen should increase to 100%
            int final_loc = ((loc_screen[1]-center)*100)/half_screen_height;

            // translate the inner image taking consideration also the density of the screen
            mImageView.setTranslationY(-final_loc * 0.4f * density);
        }
    }
}

我希望它可以帮助那些正在寻找类似功能的人.