源码:
import android.annotation.SuppressLint; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Rect; import android.graphics.drawable.BitmapDrawable; import android.graphics.drawable.Drawable; import android.support.v4.view.ViewPager; import android.util.AttributeSet; import android.util.Log; @SuppressLint("NewApi") public class ParallaxViewPager extends ViewPager { public static final int FIT_WIDTH = 0; public static final int FIT_HEIGHT = 1; public static final float OVERLAP_FULL = 1f; public static final float OVERLAP_HALF = 0.5f; public static final float OVERLAP_QUARTER = 0.25f; private static final float CORRECTION_PERCENTAGE = 0.01f; public Bitmap bitmap; private Rect source, destination; private int scaleType; private int chunkWidth; private int projectedWidth; private float overlap; private OnPageChangeListener secondOnPageChangeListener; public ParallaxViewPager(Context context) { super(context); init(); } public ParallaxViewPager(Context context, AttributeSet attrs) { super(context, attrs); init(); } private void init() { source = new Rect(); destination = new Rect(); scaleType = FIT_HEIGHT; overlap = OVERLAP_HALF; setOnPageChangeListener(new OnPageChangeListener() { @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { if (bitmap != null) { source.left = (int) Math.floor((position + positionOffset - CORRECTION_PERCENTAGE) * chunkWidth); source.right = (int) Math.ceil((position + positionOffset + CORRECTION_PERCENTAGE) * chunkWidth + projectedWidth); destination.left = (int) Math.floor((position + positionOffset - CORRECTION_PERCENTAGE) * getWidth()); destination.right = (int) Math.ceil((position + positionOffset + 1 + CORRECTION_PERCENTAGE) * getWidth()); invalidate(); } if (secondOnPageChangeListener != null) { secondOnPageChangeListener.onPageScrolled(position, positionOffset, positionOffsetPixels); } } @Override public void onPageSelected(int position) { if (secondOnPageChangeListener != null) { secondOnPageChangeListener.onPageSelected(position); } } @Override public void onPageScrollStateChanged(int state) { if (secondOnPageChangeListener != null) { secondOnPageChangeListener.onPageScrollStateChanged(state); } } }); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); destination.top = 0; destination.bottom = h; if (getAdapter() != null && bitmap != null) calculateParallaxParameters(); } private void calculateParallaxParameters() { if (bitmap.getWidth() < getWidth() && bitmap.getWidth() < bitmap.getHeight() && scaleType == FIT_HEIGHT) { Log.w(ParallaxViewPager.class.getName(), "Invalid bitmap bounds for the current device, parallax effect will not work."); } final float ratio = (float) getHeight() / bitmap.getHeight(); if (ratio != 1) { switch (scaleType) { case FIT_WIDTH: source.top = (int) ((bitmap.getHeight() - bitmap.getHeight() / ratio) / 2); source.bottom = bitmap.getHeight() - source.top; chunkWidth = (int) Math.ceil((float) bitmap.getWidth() / (float) getAdapter().getCount()); projectedWidth = chunkWidth; break; case FIT_HEIGHT: default: source.top = 0; source.bottom = bitmap.getHeight(); projectedWidth = (int) Math.ceil(getWidth() / ratio); chunkWidth = (int) Math.ceil((bitmap.getWidth() - projectedWidth) / (float) getAdapter().getCount() * overlap); break; } } } /** * Sets the background from a resource file. * * @param resid */ @Override public void setBackgroundResource(int resid) { bitmap = BitmapFactory.decodeResource(getResources(), resid); } /** * Sets the background from a Drawable. * * @param background */ @Override public void setBackground(Drawable background) { bitmap = ((BitmapDrawable) background).getBitmap(); } /** * Deprecated. * Sets the background from a Drawable. * * @param background */ @Override public void setBackgroundDrawable(Drawable background) { bitmap = ((BitmapDrawable) background).getBitmap(); } /** * Sets the background from a bitmap. * * @param bitmap * @return The ParallaxViewPager object itself. */ public ParallaxViewPager setBackground(Bitmap bitmap) { this.bitmap = bitmap; return this; } /** * Sets how the view should scale the background. The available choices are: * <ul> * <li>FIT_HEIGHT - the height of the image is resized to matched the height of the View, also stretching the width to keep the aspect ratio. The non-visible part of the bitmap is divided into equal parts, each of them sliding in at the proper position.</li> * <li>FIT_WIDTH - the width of the background image is divided into equal chunks, each taking up the whole width of the screen.</li> * </ul> * * @param scaleType * @return */ public ParallaxViewPager setScaleType(final int scaleType) { if (scaleType != FIT_WIDTH && scaleType != FIT_HEIGHT) throw new IllegalArgumentException("Illegal argument: scaleType must be FIT_WIDTH or FIT_HEIGHT"); this.scaleType = scaleType; return this; } /** * Sets the amount of overlapping with the setOverlapPercentage(final float percentage) method. This is a number between 0 and 1, the smaller it is, the slower is the background scrolling. * * @param percentage * @return The ParallaxViewPager object itself. */ public ParallaxViewPager setOverlapPercentage(final float percentage) { if (percentage <= 0 || percentage >= 1) throw new IllegalArgumentException("Illegal argument: percentage must be between 0 and 1"); overlap = percentage; return this; } /** * Recalculates the parameters of the parallax effect, useful after changes in runtime. * * @return The ParallaxViewPager object itself. */ public ParallaxViewPager invalidateParallaxParameters() { calculateParallaxParameters(); return this; } @Override protected void onDraw(Canvas canvas) { if (bitmap != null) canvas.drawBitmap(bitmap, source, destination, null); } public void addOnPageChangeListener(OnPageChangeListener listener) { secondOnPageChangeListener = listener; } }
使用:
在layout xml或者程序中创建了ParallaxViewPager之后,可以使用下面的方法来设置背景,或者也可以xml设置:
setBackgroundResource(int resid) setBackground(Drawable background) or setBackgroundDrawable(Drawable background) setBackground(Bitmap bitmap)
这就好了,你现在可以使用ParallaxViewPager的全部功能了。你可以修改背景的滚动效果来优化用户体验。你也可以使用setScaleType(final int scaleType)方法来配置视图的图像缩放方式。这个方法只能和FIT_HEIGHT搭配使用,从下面的参数中进行选择:
FIT_HEIGHT
表示缩放图像的高度以便适配视图的高度,同时缩放图像的宽度以便保持宽高比。bitmap的不可见部分被划分成相同的区域,每个区域插入到合适的位置。FIT_HEIGHT是默认值。
FIT_WIDTH
表示背景图像的宽度被划分成相同的块,每一块占满整个屏幕的宽度。这个模式不适用于视差效果,因为背景和视图的滚动速度一样。
你也可以使用setOverlapPercentage(final float percentage) 方法来设置重叠的程度。重叠程度值介于0到1之间,这个值越小背景就滚动地越慢,默认值是50%。
setContentView(R.layout.activity_main); final ParallaxViewPager parallaxViewPager = ((ParallaxViewPager) findViewById(R.id.parallaxviewpager)); parallaxViewPager .setOverlapPercentage(0.25f) .setAdapter(new PagerAdapter() //...
<com.andraskindler.parallaxviewpager.ParallaxViewPager xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/parallaxviewpager" android:layout_width="match_parent" android:background="@drawable/background" android:layout_height="match_parent" />
https://github.com/andraskindler/parallaxviewpager
滑动Viewpager时背景颜色动态过渡变化效果
http://www.itlanbao.com/code/20150816/10000/100462.html