Android 打造不一样的新手引导页面（二），Android 程序员的春天
public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.85f;
private static final float MIN_ALPHA = 0.5f;
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
int pageHeight = view.getHeight();
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 1) { // [-1,1]
// Modify the default slide transition to shrink the page as well
float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
float vertMargin = pageHeight * (1 - scaleFactor) / 2;
float horzMargin = pageWidth * (1 - scaleFactor) / 2;
if (position < 0) {
view.setTranslationX(horzMargin - vertMargin / 2);
} else {
view.setTranslationX(-horzMargin + vertMargin / 2);
}
// Scale the page down (between MIN_SCALE and 1)
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
// Fade the page relative to its size.
view.setAlpha(MIN_ALPHA +
(scaleFactor - MIN_SCALE) /
(1 - MIN_SCALE) * (1 - MIN_ALPHA));
} else { // (1,+Infinity]
// This page is way off-screen to the right.
view.setAlpha(0);
}
}
}
运行到上述的代码，效果图如下
从上述效果图可以看到，页面切换的时候，主要是页面大小的 变化，水平移动距离的变化以及透明度的变化，这些也可以从代码中体现回来,我们主要关心[-1,1]的时候就 OK，因为在[-Infinity,-1)和(1,+Infinity]的时候是不可见的。
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
page.setAlpha(0);
} else if (position <= 1) { // [-1,1]
// Modify the default slide transition to shrink the page as well
float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
float vertMargin = pageHeight * (1 - scaleFactor) / 2;
float horzMargin = pageWidth * (1 - scaleFactor) / 2;
if (position < 0) {
page.setTranslationX(horzMargin - vertMargin / 2);
} else {
page.setTranslationX(-horzMargin + vertMargin / 2);
}
// Scale the page down (between MIN_SCALE and 1)
page.setScaleX(scaleFactor);
page.setScaleY(scaleFactor);
// Fade the page relative to its size.
page.setAlpha(MIN_ALPHA +
(scaleFactor - MIN_SCALE) /
(1 - MIN_SCALE) * (1 - MIN_ALPHA));
} else { // (1,+Infinity]
// This page is way off-screen to the right.
page.setAlpha(0);
}
DepthPageTransformer
public class DepthPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.75f;
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 0) { // [-1,0]
// Use the default slide transition when moving to the left page
view.setAlpha(1);
view.setTranslationX(0);
view.setScaleX(1);
view.setScaleY(1);
} else if (position <= 1) { // (0,1]
// Fade the page out.
view.setAlpha(1 - position);
// Counteract the default slide transition
view.setTranslationX(pageWidth * -position);
// Scale the page down (between MIN_SCALE and 1)
float scaleFactor = MIN_SCALE
(1 - MIN_SCALE) * (1 - Math.abs(position));
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
} else { // (1,+Infinity]
// This page is way off-screen to the right.
view.setAlpha(0);
}
}
}
运行上述代码以后，可以看到的变化是
下面来看一下我们自己实现的两个例子
看到上述图以后，仔细分析可以看到在我们滑动的时候主要是旋转角度的 变化，并且 Y 轴旋转中心是页面的中心点，当 position<0 的时候，X 轴的中心是 view.getWidth,当 position>0 的时候，x 轴的中心是 0，代码如下。
public class CubeOutTransformer extends BaseTransformer {
@Override
protected void onTransform(View view, float position) {
view.setPivotX(position < 0f ? view.getWidth() : 0f);
view.setPivotY(view.getHeight() * 0.5f);
view.setRotationY(90f * position);
}
@Override
public boolean isPagingEnabled() {
return true;
}
}
TableTransformer
public class TableTransformer extends BaseTransformer {
private static final Matrix OFFSET_MATRIX = new Matrix();
private static final Camera OFFSET_CAMERA = new Camera();
private static final float[] OFFSET_TEMP_FLOAT = new float[2];
private static final float minScale=0.6f;
@Override
protected void onTransform(View view, float position) {
final float rotation = (position < 0 ? 30f : -30f) * Math.abs(position);
view.setTranslationX(getOffsetXForRotation(rotation, view.getWidth(), view.getHeight()));
view.setPivotX(view.getWidth() * 0.5f);
view.setPivotY(0);
view.setRotationY(rotation);
float scaleX=Math.max(1-Math.abs(position),minScale);
view.setScaleX(scaleX);
}
protected static final float getOffsetXForRotation(float degrees, int width, int height) {
OFFSET_MATRIX.reset();
OFFSET_CAMERA.save();
OFFSET_CAMERA.rotateY(Math.abs(degrees));
OFFSET_CAMERA.getMatrix(OFFSET_MATRIX);
OFFSET_CAMERA.restore();
OFFSET_MATRIX.preTranslate(-width * 0.5f, -height * 0.5f);
OFFSET_MATRIX.postTranslate(width * 0.5f, height * 0.5f);
OFFSET_TEMP_FLOAT[0] = width;
OFFSET_TEMP_FLOAT[1] = height;
OFFSET_MATRIX.mapPoints(OFFSET_TEMP_FLOAT);
return (width - OFFSET_TEMP_FLOAT[0]) * (degrees > 0.0f ? 1.0f : -1.0f);
}
}
到此我们的源码分析为止
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