Android 阴影学习

前言

Material Design 规范指导里面特别提出了阴影的重要性和如何正确使用的方法（点击传送），那我们就更加不能忽视这一点了，本篇文章就要教大家如何设置阴影，做出一个有层次感的界面。

设置方法：

android:elevation

分别设置不同数值的elevation效果如下：

layout：

 <LinearLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:orientation="horizontal">
      <TextView android:layout_width="100dp"
                android:layout_margin="2dp"
                android:layout_height="100dp"
                android:text="test"
                android:background="@android:color/white"
                android:gravity="center"
                android:elevation="1dip"
              />
      <TextView android:layout_width="100dp"
                android:layout_margin="2dp"
                android:layout_height="100dp"
                android:text="test"
                android:background="@android:color/white"
                android:gravity="center"
                android:elevation="4dip"/>
      <TextView android:layout_width="100dp"
                android:layout_margin="2dp"
                android:layout_height="100dp"
                android:text="test"
                android:background="@android:color/white"
                android:gravity="center"
                android:elevation="8dip"
              />
  </LinearLayout>

View的z值由两部分组成，elevation和translationZ.

eleavation是静态的成员，translationZ是用来做动画。

Z = elevation + translationZ

在布局中使用 android:elevation属性去定义 

在代码中使用 View.setElevation 方法去定义 

设置视图的translation，可以使用View.setTranslationZ方法 

新的ViewPropertyAnimator.z和ViewPropertyAnimator.translationZ方法可以设置视图的elevation值

在5.0 的API Demos中 Graphics-》Shadow Card Drag 和 Shadow Card stack 这两个例子就很好的使用translationZ和eleavation

Shadow Card Drag 源码：

 /*
  * Copyright (C) 2014 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package com.example.android.apis.graphics;

 import android.animation.ObjectAnimator;
 import android.app.Activity;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Outline;
 import android.graphics.Paint;
 import android.graphics.Path;
 import android.graphics.PorterDuff;
 import android.graphics.drawable.ShapeDrawable;
 import android.graphics.drawable.shapes.OvalShape;
 import android.graphics.drawable.shapes.RectShape;
 import android.graphics.drawable.shapes.RoundRectShape;
 import android.graphics.drawable.shapes.Shape;
 import android.os.Bundle;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.animation.AccelerateInterpolator;
 import android.view.animation.DecelerateInterpolator;
 import android.widget.Button;
 import android.widget.CheckBox;
 import android.widget.CompoundButton;
 import com.example.android.apis.R;

 import java.util.ArrayList;

 public class ShadowCardDrag extends Activity {
     private static final float MAX_Z_DP = 10;
     private static final float MOMENTUM_SCALE = 10;
     private static final int MAX_ANGLE = 10;

     private class CardDragState {
         long lastEventTime;
         float lastX;
         float lastY;

         float momentumX;
         float momentumY;

         public void onDown(long eventTime, float x, float y) {
             lastEventTime = eventTime;
             lastX = x;
             lastY = y;

             momentumX = 0;
             momentumY = 0;
         }

         public void onMove(long eventTime, float x, float y) {
             final long deltaT = eventTime - lastEventTime;

             if (deltaT != 0) {
                 float newMomentumX = (x - lastX) / (mDensity * deltaT);
                 float newMomentumY = (y - lastY) / (mDensity * deltaT);

                 momentumX = 0.9f * momentumX + 0.1f * (newMomentumX * MOMENTUM_SCALE);
                 momentumY = 0.9f * momentumY + 0.1f * (newMomentumY * MOMENTUM_SCALE);

                 momentumX = Math.max(Math.min((momentumX), MAX_ANGLE), -MAX_ANGLE);
                 momentumY = Math.max(Math.min((momentumY), MAX_ANGLE), -MAX_ANGLE);

                 //noinspection SuspiciousNameCombination
                 mCard.setRotationX(-momentumY);
                 //noinspection SuspiciousNameCombination
                 mCard.setRotationY(momentumX);

                 if (mShadingEnabled) {
                     float alphaDarkening = (momentumX * momentumX + momentumY * momentumY) / (90 * 90);
                     alphaDarkening /= 2;

                     int alphaByte = 0xff - ((int)(alphaDarkening * 255) & 0xff);
                     int color = Color.rgb(alphaByte, alphaByte, alphaByte);
                     mCardBackground.setColorFilter(color, PorterDuff.Mode.MULTIPLY);
                 }
             }

             lastX = x;
             lastY = y;
             lastEventTime = eventTime;
         }

         public void onUp() {
             ObjectAnimator flattenX = ObjectAnimator.ofFloat(mCard, "rotationX", 0);
             flattenX.setDuration(100);
             flattenX.setInterpolator(new AccelerateInterpolator());
             flattenX.start();

             ObjectAnimator flattenY = ObjectAnimator.ofFloat(mCard, "rotationY", 0);
             flattenY.setDuration(100);
             flattenY.setInterpolator(new AccelerateInterpolator());
             flattenY.start();
             mCardBackground.setColorFilter(null);
         }
     }

     /**
      * Simple shape example that generates a shadow casting outline.
      */
     private static class TriangleShape extends Shape {
         private final Path mPath = new Path();

         @Override
         protected void onResize(float width, float height) {
             mPath.reset();
             mPath.moveTo(0, 0);
             mPath.lineTo(width, 0);
             mPath.lineTo(width / 2, height);
             mPath.lineTo(0, 0);
             mPath.close();
         }

         @Override
         public void draw(Canvas canvas, Paint paint) {
             canvas.drawPath(mPath, paint);
         }

         @Override
         public void getOutline(Outline outline) {
             outline.setConvexPath(mPath);
         }
     }

     private final ShapeDrawable mCardBackground = new ShapeDrawable();
     private final ArrayList<Shape> mShapes = new ArrayList<Shape>();
     private float mDensity;
     private View mCard;

     private final CardDragState mDragState = new CardDragState();
     private boolean mTiltEnabled;
     private boolean mShadingEnabled;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.shadow_card_drag);

         mDensity = getResources().getDisplayMetrics().density;
         mShapes.add(new RectShape());
         mShapes.add(new OvalShape());
         float r = 10 * mDensity;
         float radii[] = new float[] {r, r, r, r, r, r, r, r};
         mShapes.add(new RoundRectShape(radii, null, null));
         mShapes.add(new TriangleShape());

         mCardBackground.getPaint().setColor(Color.WHITE);
         mCardBackground.setShape(mShapes.get(0));
         final View cardParent = findViewById(R.id.card_parent);
         mCard = findViewById(R.id.card);
         mCard.setBackground(mCardBackground);

         final CheckBox tiltCheck = (CheckBox) findViewById(R.id.tilt_check);
         tiltCheck.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
             public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                 mTiltEnabled = isChecked;
                 if (!mTiltEnabled) {
                     mDragState.onUp();
                 }
             }
         });

         final CheckBox shadingCheck = (CheckBox) findViewById(R.id.shading_check);
         shadingCheck.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
             public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                 mShadingEnabled = isChecked;
                 if (!mShadingEnabled) {
                     mCardBackground.setColorFilter(null);
                 }
             }
         });

         final Button shapeButton = (Button) findViewById(R.id.shape_select);
         shapeButton.setOnClickListener(new View.OnClickListener() {
             int index = 0;
             @Override
             public void onClick(View v) {
                 index = (index + 1) % mShapes.size();
                 mCardBackground.setShape(mShapes.get(index));
             }
         });

         /**
          * Enable any touch on the parent to drag the card. Note that this doesn't do a proper hit
          * test, so any drag (including off of the card) will work.
          *
          * This enables the user to see the effect more clearly for the purpose of this demo.
          */
         cardParent.setOnTouchListener(new View.OnTouchListener() {
             float downX;
             float downY;
             long downTime;

             @Override
             public boolean onTouch(View v, MotionEvent event) {
                 switch (event.getAction()) {
                     case MotionEvent.ACTION_DOWN:
                         downX = event.getX() - mCard.getTranslationX();
                         downY = event.getY() - mCard.getTranslationY();
                         downTime = event.getDownTime();
                         ObjectAnimator upAnim = ObjectAnimator.ofFloat(mCard, "translationZ",
                                 MAX_Z_DP * mDensity);
                         upAnim.setDuration(100);
                         upAnim.setInterpolator(new DecelerateInterpolator());
                         upAnim.start();
                         if (mTiltEnabled) {
                             mDragState.onDown(event.getDownTime(), event.getX(), event.getY());
                         }
                         break;
                     case MotionEvent.ACTION_MOVE:
                         mCard.setTranslationX(event.getX() - downX);
                         mCard.setTranslationY(event.getY() - downY);
                         if (mTiltEnabled) {
                             mDragState.onMove(event.getEventTime(), event.getX(), event.getY());
                         }
                         break;
                     case MotionEvent.ACTION_UP:
                         ObjectAnimator downAnim = ObjectAnimator.ofFloat(mCard, "translationZ", 0);
                         downAnim.setDuration(100);
                         downAnim.setInterpolator(new AccelerateInterpolator());
                         downAnim.start();
                         if (mTiltEnabled) {
                             mDragState.onUp();
                         }
                         break;
                 }
                 return true;
             }
         });
     }
 }

layout:

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright (C) 2014 The Android Open Source Project

      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

           http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
 -->
 <FrameLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/card_parent"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:clipChildren="false"
     android:clipToPadding="false"
     android:orientation="horizontal" >
     <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:orientation="horizontal">
         <CheckBox
             android:id="@+id/tilt_check"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:checked="false"
             android:text="@string/enable_tilt"/>
         <CheckBox
             android:id="@+id/shading_check"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:checked="false"
             android:text="@string/enable_shading"/>
         <Button
             android:id="@+id/shape_select"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="@string/select_shape"/>
         </LinearLayout>

     <TextView
         android:id="@+id/card"
         android:layout_width="150dp"
         android:layout_height="150dp"
         android:background="@drawable/round_rect"
         android:clipToPadding="false"
         android:gravity="center"
         android:padding="20dp"
         android:text="@string/draggable_card"
         android:textSize="20sp"
         android:elevation="2dp"/>
 </FrameLayout>

Shadow Card stack 源码：

 /*
  * Copyright (C) 2014 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package com.example.android.apis.graphics;

 import android.animation.Animator;
 import android.animation.AnimatorSet;
 import android.animation.ObjectAnimator;
 import android.app.Activity;
 import android.os.Bundle;
 import android.view.ViewGroup;
 import android.widget.TextView;

 import com.example.android.apis.R;

 import java.util.ArrayList;

 public class ShadowCardStack extends Activity {

     private static final float X_SHIFT_DP = 1000;
     private static final float Y_SHIFT_DP = 50;
     private static final float Z_LIFT_DP = 8;
     private static final float ROTATE_DEGREES = 15;

     public AnimatorSet createSet(ArrayList<Animator> items, long startDelay) {
         AnimatorSet set = new AnimatorSet();
         set.playTogether(items);
         set.setStartDelay(startDelay);
         return set;
     }

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.shadow_card_stack);

         float density = getResources().getDisplayMetrics().density;

         final ViewGroup cardParent = (ViewGroup) findViewById(R.id.card_parent);

         final float X = X_SHIFT_DP * density;
         final float Y = Y_SHIFT_DP * density;
         final float Z = Z_LIFT_DP * density;

         ArrayList<Animator> towardAnimators = new ArrayList<Animator>();
         ArrayList<Animator> expandAnimators = new ArrayList<Animator>();
         ArrayList<Animator> moveAwayAnimators = new ArrayList<Animator>();
         ArrayList<Animator> moveBackAnimators = new ArrayList<Animator>();
         ArrayList<Animator> awayAnimators = new ArrayList<Animator>();
         ArrayList<Animator> collapseAnimators = new ArrayList<Animator>();

         final int max = cardParent.getChildCount();
         for (int i = 0; i < max; i++) {
             TextView card = (TextView) cardParent.getChildAt(i);
             card.setText("Card number " + i);

             float targetY = (i - (max-1) / 2.0f) * Y;
             Animator expand = ObjectAnimator.ofFloat(card, "translationY", targetY);
             expandAnimators.add(expand);

             Animator toward = ObjectAnimator.ofFloat(card, "translationZ", i * Z);
             toward.setStartDelay(200 * ((max) - i));
             towardAnimators.add(toward);

             card.setPivotX(X_SHIFT_DP);
             Animator rotateAway = ObjectAnimator.ofFloat(card, "rotationY",
                     i == 0 ? 0 : ROTATE_DEGREES);
             rotateAway.setStartDelay(200 * ((max) - i));
             rotateAway.setDuration(100);
             moveAwayAnimators.add(rotateAway);
             Animator slideAway = ObjectAnimator.ofFloat(card, "translationX",
                     i == 0 ? 0 : X);
             slideAway.setStartDelay(200 * ((max) - i));
             slideAway.setDuration(100);
             moveAwayAnimators.add(slideAway);

             Animator rotateBack = ObjectAnimator.ofFloat(card, "rotationY", 0);
             rotateBack.setStartDelay(200 * i);
             moveBackAnimators.add(rotateBack);
             Animator slideBack = ObjectAnimator.ofFloat(card, "translationX", 0);
             slideBack.setStartDelay(200 * i);
             moveBackAnimators.add(slideBack);

             Animator away = ObjectAnimator.ofFloat(card, "translationZ", 0);
             away.setStartDelay(200 * i);
             awayAnimators.add(away);

             Animator collapse = ObjectAnimator.ofFloat(card, "translationY", 0);
             collapseAnimators.add(collapse);
         }

         AnimatorSet totalSet = new AnimatorSet();
         totalSet.playSequentially(
                 createSet(expandAnimators, 250),
                 createSet(towardAnimators, 0),

                 createSet(moveAwayAnimators, 250),
                 createSet(moveBackAnimators, 0),

                 createSet(awayAnimators, 250),
                 createSet(collapseAnimators, 0));
         totalSet.start();
         totalSet.addListener(new RepeatListener(totalSet));
     }

     public static class RepeatListener implements Animator.AnimatorListener {
         final Animator mRepeatAnimator;
         public RepeatListener(Animator repeatAnimator) {
             mRepeatAnimator = repeatAnimator;
         }

         @Override
         public void onAnimationStart(Animator animation) {}

         @Override
         public void onAnimationEnd(Animator animation) {
             if (animation == mRepeatAnimator) {
                 mRepeatAnimator.start();
             }
         }

         @Override
         public void onAnimationCancel(Animator animation) {}

         @Override
         public void onAnimationRepeat(Animator animation) {}
     }
 }

layout:

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright (C) 2014 The Android Open Source Project

      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

           http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
 -->
 <RelativeLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/card_parent"
     android:orientation="vertical"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:clipChildren="false"
     android:clipToPadding="false"
     android:gravity="center">
     <TextView
         android:layout_width="250dp"
         android:layout_height="150dp"
         android:background="@drawable/round_rect"
         android:padding="20dp"
         android:textSize="20sp" />
     <TextView
         android:layout_width="250dp"
         android:layout_height="150dp"
         android:background="@drawable/round_rect"
         android:padding="20dp"
         android:textSize="20sp" />
     <TextView
         android:layout_width="250dp"
         android:layout_height="150dp"
         android:background="@drawable/round_rect"
         android:padding="20dp"
         android:textSize="20sp" />
     <TextView
         android:layout_width="250dp"
         android:layout_height="150dp"
         android:background="@drawable/round_rect"
         android:padding="20dp"
         android:textSize="20sp" />
     <TextView
         android:layout_width="250dp"
         android:layout_height="150dp"
         android:background="@drawable/round_rect"
         android:padding="20dp"
         android:textSize="20sp" />