畫面投影片是指在一個畫面之間轉換,也是 UI 常見的轉場效果
例如設定精靈或投影播放本課程將說明如何使用
支援資料庫提供的 ViewPager
。
ViewPager
物件可以為畫面投影片加入動畫
。這是畫面投影片的轉場效果
下一個畫面的內容:
ViewPager
為 AndroidX 的一部分若需更多資訊,請參閲
使用 AndroidX。
建立檢視畫面
建立稍後用於片段內容的版面配置檔案。您也需要 定義片段內容的字串。以下範例 包含文字檢視區塊,可顯示一些文字:
<!-- fragment_screen_slide_page.xml --> <ScrollView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/content" android:layout_width="match_parent" android:layout_height="match_parent" > <TextView style="?android:textAppearanceMedium" android:padding="16dp" android:lineSpacingMultiplier="1.2" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/lorem_ipsum" /> </ScrollView>
建立片段
建立 Fragment
類別,以傳回版面配置
您在 onCreateView()
中建立的
方法。這樣一來,每當您需要新網頁時,就可以在父項活動中建立這個片段的例項。
向使用者顯示:
Kotlin
import android.support.v4.app.Fragment class ScreenSlidePageFragment : Fragment() { override fun onCreateView( inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View = inflater.inflate(R.layout.fragment_screen_slide_page, container, false) }
Java
import android.support.v4.app.Fragment; ... public class ScreenSlidePageFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { ViewGroup rootView = (ViewGroup) inflater.inflate( R.layout.fragment_screen_slide_page, container, false); return rootView; } }
新增 ViewPager
ViewPager
物件內建可轉換的滑動手勢
而且預設會顯示螢幕投影片動畫,因此您不必建立
自製動畫ViewPager
使用
PagerAdapter
物件做為顯示新頁面的供應項目,因此 PagerAdapter
會使用
您稍早建立的片段類別。
首先,請建立包含 ViewPager
的版面配置:
<!-- activity_screen_slide.xml --> <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="match_parent" />
建立可執行下列操作的活動:
- 將內容檢視畫面設為使用
ViewPager
的版面配置。 - 建立擴充
FragmentStatePagerAdapter
抽象類別的類別並實作 要提供的getItem()
方法 將ScreenSlidePageFragment
視為新頁面。此外,Pager 轉接程式也規定,您必須實作getCount()
方法,會傳回轉接程式會建立的頁面數量 (本例中為五個方法)。 - 將
PagerAdapter
連結至ViewPager
。
Kotlin
import android.support.v4.app.Fragment import android.support.v4.app.FragmentManager ... /** * The number of pages (wizard steps) to show in this demo. */ private const val NUM_PAGES = 5 class ScreenSlidePagerActivity : FragmentActivity() { /** * The pager widget, which handles animation and allows swiping horizontally to access previous * and next wizard steps. */ private lateinit var mPager: ViewPager override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_screen_slide) // Instantiate a ViewPager and a PagerAdapter. mPager = findViewById(R.id.pager) // The pager adapter, which provides the pages to the view pager widget. val pagerAdapter = ScreenSlidePagerAdapter(supportFragmentManager) mPager.adapter = pagerAdapter } override fun onBackPressed() { if (mPager.currentItem == 0) { // If the user is currently looking at the first step, allow the system to handle the // Back button. This calls finish() on this activity and pops the back stack. super.onBackPressed() } else { // Otherwise, select the previous step. mPager.currentItem = mPager.currentItem - 1 } } /** * A simple pager adapter that represents 5 ScreenSlidePageFragment objects, in * sequence. */ private inner class ScreenSlidePagerAdapter(fm: FragmentManager) : FragmentStatePagerAdapter(fm) { override fun getCount(): Int = NUM_PAGES override fun getItem(position: Int): Fragment = ScreenSlidePageFragment() } }
Java
import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; ... public class ScreenSlidePagerActivity extends FragmentActivity { /** * The number of pages (wizard steps) to show in this demo. */ private static final int NUM_PAGES = 5; /** * The pager widget, which handles animation and allows swiping horizontally to access previous * and next wizard steps. */ private ViewPager mPager; /** * The pager adapter, which provides the pages to the view pager widget. */ private PagerAdapter pagerAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_screen_slide); // Instantiate a ViewPager and a PagerAdapter. mPager = (ViewPager) findViewById(R.id.pager); pagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager()); mPager.setAdapter(pagerAdapter); } @Override public void onBackPressed() { if (mPager.getCurrentItem() == 0) { // If the user is currently looking at the first step, allow the system to handle the // Back button. This calls finish() on this activity and pops the back stack. super.onBackPressed(); } else { // Otherwise, select the previous step. mPager.setCurrentItem(mPager.getCurrentItem() - 1); } } /** * A simple pager adapter that represents 5 ScreenSlidePageFragment objects, in * sequence. */ private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter { public ScreenSlidePagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int position) { return new ScreenSlidePageFragment(); } @Override public int getCount() { return NUM_PAGES; } } }
使用 PageTransformer 自訂動畫
如要顯示與預設畫面投影片動畫不同的動畫,請實作
ViewPager.PageTransformer
介面並提供給
介面公開單一方法 transformPage()
。畫面轉換的每個時間點,對每個可見頁面 (通常只有一個可見頁面) 以及位於畫面外的相鄰網頁呼叫一次此方法。
舉例來說,假設第 3 頁顯示後,使用者拖曳到第 4 頁,
已呼叫 transformPage()
。
實作 transformPage()
時,
然後建立自訂投影片動畫,並根據需要轉換的頁面
網頁的位置 (從 position
參數取得)
transformPage()
方法。
position
參數會指出指定網頁相對於畫面中央的位置。
這類動態屬性會隨著使用者捲動網頁而改變。網頁填滿螢幕時,網頁的排名值為 0
。
如果頁面偏離畫面右側,則頁面的位置值為 1
。如果使用者從第 1 頁和第 2 頁之間捲動網頁,第 1 頁的排名為 -0.5,而第 2 頁的排名為 0.5。您可以依螢幕上的位置建立自訂投影片動畫,方法是使用 setAlpha()
、setTranslationX()
或
setScaleY()
。
實作 PageTransformer
時,
透過以下方式致電setPageTransformer()
:
實作自訂動畫舉例來說
已命名PageTransformer
ZoomOutPageTransformer
,您可以設定自訂動畫
輸入:
Kotlin
val mPager: ViewPager = findViewById(R.id.pager) ... mPager.setPageTransformer(true, ZoomOutPageTransformer())
Java
ViewPager mPager = (ViewPager) findViewById(R.id.pager); ... mPager.setPageTransformer(true, new ZoomOutPageTransformer());
請參閱縮小頁面轉換器和深度頁面轉換器
提供 PageTransformer
的範例與影片。
縮小頁面轉換器
這個頁面轉換器在切換頁面時,會縮小及淡出頁面 相鄰的網頁。網頁越靠近中央, 確保其正常大小並淡入
Kotlin
private const val MIN_SCALE = 0.85f private const val MIN_ALPHA = 0.5f class ZoomOutPageTransformer : ViewPager.PageTransformer { override fun transformPage(view: View, position: Float) { view.apply { val pageWidth = width val pageHeight = height when { position < -1 -> { // [-Infinity,-1) // This page is way off-screen to the left. alpha = 0f } position <= 1 -> { // [-1,1] // Modify the default slide transition to shrink the page as well val scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position)) val vertMargin = pageHeight * (1 - scaleFactor) / 2 val horzMargin = pageWidth * (1 - scaleFactor) / 2 translationX = if (position < 0) { horzMargin - vertMargin / 2 } else { horzMargin + vertMargin / 2 } // Scale the page down (between MIN_SCALE and 1) scaleX = scaleFactor scaleY = scaleFactor // Fade the page relative to its size. alpha = (MIN_ALPHA + (((scaleFactor - MIN_SCALE) / (1 - MIN_SCALE)) * (1 - MIN_ALPHA))) } else -> { // (1,+Infinity] // This page is way off-screen to the right. alpha = 0f } } } } }
Java
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(0f); } 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(0f); } } }
深度頁面轉換工具
此頁面轉換器使用用於滑動頁面的預設投影片動畫 使用「深度」時將頁面滑動到 沒錯這種深度動畫會將頁面淡出,然後線性縮小。
播放深度動畫時,預設動畫 (畫面滑動) 仍會保持 因此,您必須以負數的 X 翻譯反對螢幕投影片。 例如:
Kotlin
view.translationX = -1 * view.width * position
Java
view.setTranslationX(-1 * view.getWidth() * position);
以下範例說明如何對應預設畫面投影片動畫 操作頁面轉換器中:
Kotlin
private const val MIN_SCALE = 0.75f class DepthPageTransformer : ViewPager.PageTransformer { override fun transformPage(view: View, position: Float) { view.apply { val pageWidth = width when { position < -1 -> { // [-Infinity,-1) // This page is way off-screen to the left. alpha = 0f } position <= 0 -> { // [-1,0] // Use the default slide transition when moving to the left page alpha = 1f translationX = 0f scaleX = 1f scaleY = 1f } position <= 1 -> { // (0,1] // Fade the page out. alpha = 1 - position // Counteract the default slide transition translationX = pageWidth * -position // Scale the page down (between MIN_SCALE and 1) val scaleFactor = (MIN_SCALE + (1 - MIN_SCALE) * (1 - Math.abs(position))) scaleX = scaleFactor scaleY = scaleFactor } else -> { // (1,+Infinity] // This page is way off-screen to the right. alpha = 0f } } } } }
Java
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(0f); } else if (position <= 0) { // [-1,0] // Use the default slide transition when moving to the left page view.setAlpha(1f); view.setTranslationX(0f); view.setScaleX(1f); view.setScaleY(1f); } 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(0f); } } }