文章概览
- 1 Android动画概述
- 1.1 动画的分类
- 1.2 视图动画与属性动画的区别
- 2 视图动画View Animation
- 2.1 补间动画Tween Animation
- 2.1.1 XML中用标签实现补间动画
- 2.1.2 代码实现补间动画
- 2.2 逐帧动画Frame Animation
- 2.2.1 XML实现逐帧动画
- 2.2.2 代码实现逐帧动画
本系列将介绍以下内容：
1 Android动画概述
1.1 动画的分类
Android中共有两种类型的动画，View Animation(视图动画)和Property Animation(属性动画)。
其中View Animation包括Tween Animation(补间动画)和Frame Animation(逐帧动画)，Property Animation包括ValueAnimator和ObjectAnimator。
在API Level 12（Android 3.1）时又引入了ViewPropertyAnimator来完善属性动画。
1.2 视图动画与属性动画的区别
1、引入时间不同
View Animation是在API Level 1（Android 1.0）时引入的；
Property Animation是在API Level 11（Android 3.0）时引入的；
ViewPropertyAnimator是在API Level 12（Android 3.1）时引入的。
因此，Property Animation是用来弥补View Animation的不足。
2、所在的包不同
View Animation中Tween Animation的相关API位于包android.view.animation中，Frame Animation的相关API位于包android.graphics.drawable中；
Property Animation相关API位于包android.animation中；
ViewPropertyAnimator类位于包android.view中。
3、动画类的命名不同
View Animation中的补间动画类都命名为XxxAnimation，逐帧动画由AnimationDrawable类单独完成；
Property Animation中的动画类都命名为XxxAnimator；
ViewPropertyAnimator使得view控件可以直接调用相关动画API，如textView.animate().alpha(0f)。
4、动画原理不同
视图动画中的补间动画主要是实现控件的渐入渐出、移动、旋转、缩放等效果，且并没有改变控件的相关属性的值，而逐帧动画主要是用来实现“动画”的。
视图动画只能对派生自View类的控件起作用，而属性动画是作用于控件属性，通过改变控件某一属性值来做动画的。
2 视图动画View Animation
视图动画是在API Level 1（Android 1.0）时引入的，包括补间动画和逐帧动画，它们有两种实现方式，一是在XML中用标签实现，二是用代码实现。
2.1 补间动画Tween Animation
补间动画位于包android.view.animation中，主要由抽象类Animation及其五个具体类来实现，其UML图（类图Class Diagram）如图所示：
抽象类Animation包含一个接口AnimationListener和两个具体类NoImagePreloadHolder、Description，详见源码。
补间动画有两种实现方式，一是使用标签，二是代码实现，其对应关系如下：
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抽象类Animation及其全部5个子类：
package java.lang;
/**
* Cloneable是一个空接口，什么都没有
*/
public interface Cloneable {
}
package android.view.animation;
public abstract class Animation implements Cloneable {
...
private static class NoImagePreloadHolder {
public static final boolean USE_CLOSEGUARD
= SystemProperties.getBoolean("log.closeguard.Animation", false);
}
boolean mInitialized = false;
Interpolator mInterpolator;
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 117519981)
private AnimationListener mListener;
@Override
protected Animation clone() throws CloneNotSupportedException {
final Animation animation = (Animation) super.clone();
animation.mPreviousRegion = new RectF();
animation.mRegion = new RectF();
animation.mTransformation = new Transformation();
animation.mPreviousTransformation = new Transformation();
return animation;
}
public void reset() {
mPreviousRegion.setEmpty();
mPreviousTransformation.clear();
mInitialized = false;
mCycleFlip = false;
mRepeated = 0;
mMore = true;
mOneMoreTime = true;
mListenerHandler = null;
}
public void cancel() {
if (mStarted && !mEnded) {
fireAnimationEnd();
mEnded = true;
guard.close();
}
// Make sure we move the animation to the end
mStartTime = Long.MIN_VALUE;
mMore = mOneMoreTime = false;
}
public boolean isInitialized() {
return mInitialized;
}
public void initialize(int width, int height, int parentWidth, int parentHeight) {
reset();
mInitialized = true;
}
public void setAnimationListener(AnimationListener listener) {
mListener = listener;
}
public void setInterpolator(Context context, @AnimRes @InterpolatorRes int resID) {
setInterpolator(AnimationUtils.loadInterpolator(context, resID));
}
public void setInterpolator(Interpolator i) {
mInterpolator = i;
}
public void setDuration(long durationMillis) {
if (durationMillis < 0) {
throw new IllegalArgumentException("Animation duration cannot be negative");
}
mDuration = durationMillis;
}
public void setRepeatMode(int repeatMode) {
mRepeatMode = repeatMode;
}
public void setRepeatCount(int repeatCount) {
if (repeatCount < 0) {
repeatCount = INFINITE;
}
mRepeatCount = repeatCount;
}
public Interpolator getInterpolator() {
return mInterpolator;
}
...
protected static class Description {
...
}
public static interface AnimationListener {
void onAnimationStart(Animation animation);
void onAnimationEnd(Animation animation);
void onAnimationRepeat(Animation animation);
}
}
package android.view.animation;
public class AlphaAnimation extends Animation {
...
}
package android.view.animation;
public class ScaleAnimation extends Animation {
...
}
package android.view.animation;
public class TranslateAnimation extends Animation {
...
}
package android.view.animation;
public class RotateAnimation extends Animation {
...
}
package android.view.animation;
public class AnimationSet extends Animation {
...
public void addAnimation(Animation a) {
...
}
...
}
2.1.1 XML中用标签实现补间动画
标签文件应放在res/anim目录下，使用R.anim.xxx访问；也可以放在res/drawable目录下，使用R.drawable.xxx访问。
应用举例，定义几个动画标签文件：
<?xml version="1.0" encoding="utf-8"?>
<alpha xmlns:android="http://schemas.android.com/apk/res/android"
android:duration="3000"
android:fillBefore="true"
android:fromAlpha="1.0"
android:toAlpha="0.1">
</alpha>
<?xml version="1.0" encoding="utf-8"?>
<rotate xmlns:android="http://schemas.android.com/apk/res/android"
android:duration="3000"
android:fillAfter="true"
android:fromDegrees="0"
android:pivotX="100%"
android:pivotY="100%"
android:toDegrees="-650">
</rotate>
<?xml version="1.0" encoding="utf-8"?>
<scale xmlns:android="http://schemas.android.com/apk/res/android"
android:duration="700"
android:fillBefore="true"
android:fromXScale="1.0"
android:fromYScale="1.2"
android:pivotX="50%"
android:pivotY="50%"
android:repeatCount="1"
android:repeatMode="reverse"
android:toXScale="0.4"
android:toYScale="0.6" />
<?xml version="1.0" encoding="utf-8"?>
<translate xmlns:android="http://schemas.android.com/apk/res/android"
android:duration="2000"
android:fromXDelta="0"
android:fromYDelta="0"
android:toXDelta="-80"
android:toYDelta="-80">
</translate>
<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
android:duration="3000"
android:fillAfter="true">
<alpha
android:fromAlpha="0.0"
android:toAlpha="1.0" />
<scale
android:fromXScale="0.0"
android:fromYScale="0.0"
android:pivotX="50%"
android:pivotY="50%"
android:toXScale="1.4"
android:toYScale="1.4" />
<rotate
android:fromDegrees="0"
android:pivotX="50%"
android:pivotY="50%"
android:toDegrees="720" />
<translate
android:duration="2000"
android:fromXDelta="0"
android:fromYDelta="0"
android:toXDelta="-80"
android:toYDelta="-80" />
</set>
布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<Button
android:id="@+id/anim_xml_activity"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="XML生成动画"
android:textAllCaps="false"
android:textSize="18sp" />
<Button
android:id="@+id/anim_java_activity"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="代码生成动画"
android:textAllCaps="false"
android:textSize="18sp" />
</LinearLayout>
和
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<Button
android:id="@+id/btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="Start Anim"
android:textAllCaps="false"
android:textSize="18sp" />
<TextView
android:id="@+id/tv"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_gravity="center_horizontal"
android:background="@android:color/darker_gray"
android:gravity="center"
android:text="Hello World"
android:textSize="18sp" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>
点击按钮时给TextView应用动画
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.TextView;
public class AnimationXMLActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.animation_xml_activity);
final TextView tv = (TextView) findViewById(R.id.tv);
findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// 缩放动画
Animation scaleAnim = AnimationUtils.loadAnimation(AnimationXMLActivity.this, R.anim.scaleAnim);
// 透明度动画
Animation alphaAnim = AnimationUtils.loadAnimation(AnimationXMLActivity.this, R.anim.alphaAnim);
// 旋转动画
Animation rotateAnim = AnimationUtils.loadAnimation(AnimationXMLActivity.this, R.anim.rotateAnim);
// 平移动画
Animation translateAnim = AnimationUtils.loadAnimation(AnimationXMLActivity.this, R.anim.translateAnim);
// 动画集合
Animation setAnim = AnimationUtils.loadAnimation(AnimationXMLActivity.this, R.anim.setAnim);
// 开启动画
tv.startAnimation(scaleAnim);
// tv.startAnimation(alphaAnim);
// tv.startAnimation(rotateAnim);
// tv.startAnimation(translateAnim);
// tv.startAnimation(setAnim);
}
});
}
}
标签使用较简单，效果图：
用法要点1，使用AnimationUtils.loadAnimation(Context context, @AnimRes int id)加载动画标签，详见源码。
注意：
Property Animation(属性动画)用XML形式实现动画的方式是调用类方法AnimatorInflater.loadAnimator(xxx)，该方法返回值是Animator。
package android.view.animation
public class AnimationUtils {
...
public static Animation loadAnimation(Context context, @AnimRes int id)
throws NotFoundException {
XmlResourceParser parser = null;
try {
parser = context.getResources().getAnimation(id);
return createAnimationFromXml(context, parser);
} catch (XmlPullParserException | IOException ex) {
throw new NotFoundException(
"Can't load animation resource ID #0x" + Integer.toHexString(id), ex);
} finally {
if (parser != null) parser.close();
}
}
...
}
用法要点2，使用View的startAnimation(Animation animation)开启动画，源码：
package android.view;
@UiThread
public class View implements Drawable.Callback, KeyEvent.Callback,
AccessibilityEventSource {
...
protected Animation mCurrentAnimation = null;
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023)
private ViewPropertyAnimator mAnimator = null;
public void startAnimation(Animation animation) {
animation.setStartTime(Animation.START_ON_FIRST_FRAME);
setAnimation(animation);
invalidateParentCaches();
invalidate(true);
}
public ViewPropertyAnimator animate() {
if (mAnimator == null) {
mAnimator = new ViewPropertyAnimator(this);
}
return mAnimator;
}
...
}
2.1.2 代码实现补间动画
标签中定义的效果可以用代码实现，例如前例中的alpha标签用代码实现就是：
final TextView tv = (TextView) findViewById(R.id.tv);
findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
AlphaAnimation alphaAnim = new AlphaAnimation(1.0f, 0.1f);
alphaAnim.setDuration(3000);
alphaAnim.setFillBefore(true);
tv.startAnimation(alphaAnim);
}
其余标签的代码实现方法类似，参考下述代码：
import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.view.View;
import android.view.animation.*;
import android.widget.TextView;
public class AnimationJAVAActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.animation_java_activity);
final TextView tv = (TextView) findViewById(R.id.tv);
findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// ScaleAnimation
ScaleAnimation scaleAnim = new ScaleAnimation(
0.0f,
1.4f,
0.0f,
1.4f,
Animation.RELATIVE_TO_SELF,
0.5f,
Animation.RELATIVE_TO_SELF,
0.5f
);
scaleAnim.setDuration(700);
// AlphaAnimation
AlphaAnimation alphaAnim = new AlphaAnimation(1.0f, 0.1f);
alphaAnim.setDuration(3000);
alphaAnim.setFillBefore(true);
// RotateAnimation
RotateAnimation rotateAnim = new RotateAnimation(
0,
-650,
Animation.RELATIVE_TO_SELF,
0.5f,
Animation.RELATIVE_TO_SELF,
0.5f
);
rotateAnim.setDuration(3000);
rotateAnim.setFillAfter(true);
// TranslateAnimation
TranslateAnimation translateAnim = new TranslateAnimation(
Animation.ABSOLUTE,
0,
Animation.ABSOLUTE,
-80,
Animation.ABSOLUTE,
0,
Animation.ABSOLUTE,
-80
);
translateAnim.setDuration(2000);
translateAnim.setFillBefore(true);
// AnimationSet的用法
Animation alpha_Anim = new AlphaAnimation(1.0f, 0.1f);
Animation scale_Anim = new ScaleAnimation(
0.0f,
1.4f,
0.0f,
1.4f,
Animation.RELATIVE_TO_SELF,
0.5f,
Animation.RELATIVE_TO_SELF,
0.5f
);
Animation rotate_Anim = new RotateAnimation(
0,
720,
Animation.RELATIVE_TO_SELF,
0.5f,
Animation.RELATIVE_TO_SELF,
0.5f
);
AnimationSet setAnim = new AnimationSet(true);
// AnimationSet的addAnimation(Animation a)添加动画
setAnim.addAnimation(alpha_Anim);
setAnim.addAnimation(scale_Anim);
setAnim.addAnimation(rotate_Anim);
setAnim.setDuration(3000);
setAnim.setFillAfter(true);
// tv.startAnimation(scaleAnim);
// tv.startAnimation(alphaAnim);
// tv.startAnimation(rotateAnim);
// tv.startAnimation(translateAnim);
tv.startAnimation(setAnim);
}
});
}
}
Animation有动画监听方法，其用法是：
private void animListener(final TextView tv) {
final RotateAnimation rotateAnim = new RotateAnimation(
0,
-650,
Animation.RELATIVE_TO_SELF,
0.5f,
Animation.RELATIVE_TO_SELF,
0.5f
);
rotateAnim.setDuration(3000);
rotateAnim.setFillAfter(true);
ScaleAnimation scaleAnim = new ScaleAnimation(
0.0f,
1.4f,
0.0f,
1.4f,
Animation.RELATIVE_TO_SELF,
0.5f,
Animation.RELATIVE_TO_SELF,
0.5f
);
scaleAnim.setDuration(700);
scaleAnim.setAnimationListener(new Animation.AnimationListener() {
public void onAnimationStart(Animation animation) {
}
public void onAnimationEnd(Animation animation) {
tv.startAnimation(rotateAnim);
}
public void onAnimationRepeat(Animation animation) {
}
});
tv.startAnimation(scaleAnim);
}
效果图参考上图示例。
2.2 逐帧动画Frame Animation
逐帧动画就是一帧一帧的播放动画，就像放电影一样。
逐帧动画既可以通过XML实现，也可以用代码实现，且这两种实现方式均由AnimationDrawable类完成。它位于包android.graphics.drawable中，是Drawable抽象类的间接子类，它主要用来创建一个逐帧动画，并对帧进行拉伸，把它设置为View的背景，即可使用AnimationDrawable.start()播放动画，其类图如图所示：
Drawable内部定义了一个接口Callback和一个抽象类ConstantState；
DrawableContainer内部定义了一个抽象类DrawableContainerState（继承自ConstantState）和具体类BlockInvalidateCallback；
AnimationDrawable内部定义了具体类AnimationState（继承自DrawableContainerState），其源码见下文。
Animatable接口、Drawable抽象类、DrawableContainer类、AnimationDrawable类均位于包android.graphics.drawable中。
2.2.1 XML实现逐帧动画
逐帧动画也可以用XML方式实现，它使用< animation-list />标签，其具体用法是：
1、将一帧一帧的动画图片存放在res.drawable或res.mipmap目录下
2、在res.anim或res.drawable中新建xml文件，如playing_ani.xml，引用存放的那几帧图片，如
<?xml version="1.0" encoding="UTF-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
android:oneshot="false">
<item
android:drawable="@drawable/list_icon_gif_playing1"
android:duration="60" />
<item
android:drawable="@drawable/list_icon_gif_playing2"
android:duration="60" />
<item
android:drawable="@drawable/list_icon_gif_playing3"
android:duration="60" />
</animation-list>
3、在布局文件中定义ImageView（继承自View），并在其属性android:src或android:background中引用动画帧。
使用android:src时，用ImageView.getDrawable()获取资源。
使用android:background时，用View.getBackground()获取资源。
上述两种获取资源的方法都返回一个Drawable，区别是该Drawable是定义在View中还是ImageView中。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center_horizontal"
android:orientation="vertical">
<ImageView
android:id="@+id/frame_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:src="@drawable/playing_ani" />
<ImageView
android:id="@+id/frame_image2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:background="@drawable/playing_ani" />
</LinearLayout>
ImageView继承自View，且都与Drawable关联。
package android.graphics.drawable;
public abstract class Drawable {
...
public interface Callback {
void invalidateDrawable(@NonNull Drawable who);
void scheduleDrawable(@NonNull Drawable who, @NonNull Runnable what, long when);
void unscheduleDrawable(@NonNull Drawable who, @NonNull Runnable what);
}
public static abstract class ConstantState {
...
}
...
}
package android.graphics.drawable;
public class BitmapDrawable extends Drawable {
...
final static class BitmapState extends ConstantState {
...
}
}
package android.view;
@UiThread
public class View implements Drawable.Callback, KeyEvent.Callback,
AccessibilityEventSource {
...
@ViewDebug.ExportedProperty(deepExport = true, prefix = "bg_")
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
private Drawable mBackground;
@InspectableProperty
public Drawable getBackground() {
return mBackground;
}
...
}
package android.widget;
@RemoteView
public class ImageView extends View {
...
@UnsupportedAppUsage
private Drawable mDrawable = null;
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
private BitmapDrawable mRecycleableBitmapDrawable = null;
/**
* Gets the current Drawable, or null if no Drawable has been
* assigned.
*
* @return the view's drawable, or null if no drawable has been
* assigned.
*/
@InspectableProperty(name = "src")
public Drawable getDrawable() {
if (mDrawable == mRecycleableBitmapDrawable) {
// Consider our cached version dirty since app code now has a reference to it
mRecycleableBitmapDrawable = null;
}
return mDrawable;
}
...
}
4、使用AnimationDrawable开始动画
ImageView imgView = findViewById(R.id.frame_image);
// 此处要强转为AnimationDrawable
AnimationDrawable animDrawable = (AnimationDrawable) imgView.getDrawable();
//AnimationDrawable animDrawable = (AnimationDrawable) imgView.getBackground();
animDrawable.start();
与AnimationDrawable有关的源码如下所示：
package android.graphics.drawable;
/**
* Interface that drawables supporting animations should implement.
*/
public interface Animatable {
void start();
void stop();
boolean isRunning();
}
package java.lang;
@FunctionalInterface
public interface Runnable {
public abstract void run();
}
package android.graphics.drawable;
public class DrawableContainer extends Drawable implements Drawable.Callback {
...
public abstract static class DrawableContainerState extends ConstantState {
public final int addChild(Drawable dr) {
...
}
...
}
private static class BlockInvalidateCallback implements Drawable.Callback {
...
}
}
package android.graphics.drawable;
public class AnimationDrawable extends DrawableContainer implements Runnable, Animatable {
private AnimationState mAnimationState;
@UnsupportedAppUsage
private int mCurFrame = 0;
private boolean mRunning;
private boolean mAnimating;
@Override
public void start() {
mAnimating = true;
if (!isRunning()) {
// Start from 0th frame.
setFrame(0, false, mAnimationState.getChildCount() > 1
|| !mAnimationState.mOneShot);
}
}
@Override
public void stop() {
mAnimating = false;
if (isRunning()) {
mCurFrame = 0;
unscheduleSelf(this);
}
}
@Override
public boolean isRunning() {
return mRunning;
}
public void setOneShot(boolean oneShot) {
mAnimationState.mOneShot = oneShot;
}
public void addFrame(@NonNull Drawable frame, int duration) {
mAnimationState.addFrame(frame, duration);
if (!mRunning) {
setFrame(0, true, false);
}
}
private void setFrame(int frame, boolean unschedule, boolean animate) {
if (frame >= mAnimationState.getChildCount()) {
return;
}
mAnimating = animate;
mCurFrame = frame;
selectDrawable(frame);
if (unschedule || animate) {
unscheduleSelf(this);
}
if (animate) {
// Unscheduling may have clobbered these values; restore them
mCurFrame = frame;
mRunning = true;
scheduleSelf(this, SystemClock.uptimeMillis() + mAnimationState.mDurations[frame]);
}
}
...
private final static class AnimationState extends DrawableContainerState {
private int[] mDurations;
private boolean mOneShot = false;
public void addFrame(Drawable dr, int dur) {
int pos = super.addChild(dr);
mDurations[pos] = dur;
}
...
}
...
}
一个完整的XML实现的Demo:
布局文件main_activity
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<Button
android:id="@+id/xml_create"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="XML生成动画"
android:textAllCaps="false"
android:textSize="18sp" />
<Button
android:id="@+id/java_create"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="代码生成动画"
android:textAllCaps="false"
android:textSize="18sp" />
</LinearLayout>
布局文件frame_anim_xml_activity.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal">
<Button
android:id="@+id/start_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="start"
android:textAllCaps="false"
android:textSize="18sp" />
<Button
android:id="@+id/stop_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="150dp"
android:text="stop"
android:textAllCaps="false"
android:textSize="18sp" />
<ImageView
android:id="@+id/frame_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dp"
android:background="@drawable/playing_ani" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>
实现代码
package com.example.FrameAnim;
import android.app.Activity;
import android.graphics.drawable.AnimationDrawable;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
public class FrameAnimXMLActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.frame_anim_xml_activity);
ImageView image = (ImageView) findViewById(R.id.frame_image);
final AnimationDrawable anim = (AnimationDrawable) image.getBackground();
findViewById(R.id.start_btn).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
anim.start();
}
});
findViewById(R.id.stop_btn).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
anim.stop();
}
});
}
}
效果图：
2.2.2 代码实现逐帧动画
代码实现方式主要是由AnimationDrawable.addFrame(xxx)完成，它可以添加动画帧并设置持续时间。
布局文件与XML实现方式一样，需要有一个ImageView但不需要设置其src或background属性。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center_horizontal"
android:orientation="vertical">
<ImageView
android:id="@+id/frame_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp" />
</LinearLayout>
主要是实现代码与XML方式有所区别，该方式不需要在xml中引用帧图，全部在代码中添加：
package com.example.FrameAnim;
import android.app.Activity;
import android.graphics.drawable.AnimationDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.widget.ImageView;
public class FrameAnimJAVAActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.frame_anim_java_activity);
ImageView image = findViewById(R.id.frame_image);
final AnimationDrawable anim = new AnimationDrawable();
// 添加14帧图片
for (int i = 1; i <= 14; i++) {
// 难点：通过文件名拿到对应资源的ID（请看getIdentifier(xxx)源码）
int id = getResources().getIdentifier("list_icon_gif_playing" + i, "drawable", getPackageName());
Drawable drawable = getResources().getDrawable(id);
anim.addFrame(drawable, 60);
}
anim.setOneShot(false);
image.setBackgroundDrawable(anim);
anim.start();
}
}
效果图见上图示例。
至此，逐帧动画的代码实现方式也由AnimationDrawable完成了。
参考文献：
[1] UML中的类图及类图之间的关系
[2] 启舰.Android自定义控件开发入门与实战[M].北京:电子工业出版社，2018
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