帧动画实现
Android的动画分为三大类：帧动画，补间动画，属性动画。帧动画是实现原理最简单，是在短时间连续播放多张照片，模拟动态画面的效果。
帧动画由动画图形AnimationDrawable生成。
常用方法
| 方法 | 解释 |
|---|---|
| addFrame | 添加一幅图片帧，并指定时间 |
| setOneShot | 设置是否只播放一次 |
| start | 开始播放 |
| stop | 结束播放 |
| isRunning | 是否正在播放 |
使用
public class FrameAnimationActivity extends AppCompatActivity implements View.OnClickListener {
private ImageView ivFrameAnim;
private AnimationDrawable ad_frame;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_frame_animation);
ivFrameAnim = findViewById(R.id.iv_frame_anim);
ivFrameAnim.setOnClickListener(this);
showFrameAnimByCode();
}
private void showFrameAnimByCode() {
// 创建一个帧动画
ad_frame = new AnimationDrawable();
// 下面把每帧图片加入到帧动画的队列中
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p1), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p2), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p3), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p4), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p5), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p6), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p7), 50);
ad_frame.addFrame(getResources().getDrawable(R.drawable.flow_p8), 50);
// 设置帧动画是否只播放一次。为true表示只播放一次，为false表示循环播放
ad_frame.setOneShot(false);
// 设置图像视图的图形为帧动画
ivFrameAnim.setImageDrawable(ad_frame);
ad_frame.start(); // 开始播放帧动画
}
@Override
public void onClick(View view) {
if (view.getId() == R.id.iv_frame_anim) {
if (ad_frame.isRunning()) {
// 判断帧动画是否正在播放
ad_frame.stop(); // 停止播放帧动画
} else {
ad_frame.start(); // 开始播放帧动画
}
}
}
}
除了在代码中添加帧图片，还可以用xml来定义。
frame_anim
<?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/flow_p1"
android:duration="50" />
<item
android:drawable="@drawable/flow_p2"
android:duration="50" />
<item
android:drawable="@drawable/flow_p3"
android:duration="50" />
<item
android:drawable="@drawable/flow_p4"
android:duration="50" />
<item
android:drawable="@drawable/flow_p5"
android:duration="50" />
<item
android:drawable="@drawable/flow_p6"
android:duration="50" />
<item
android:drawable="@drawable/flow_p7"
android:duration="50" />
<item
android:drawable="@drawable/flow_p8"
android:duration="50" />
</animation-list>
public class FrameAnimationActivity extends AppCompatActivity implements View.OnClickListener {
private ImageView ivFrameAnim;
private AnimationDrawable ad_frame;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_frame_animation);
ivFrameAnim = findViewById(R.id.iv_frame_anim);
ivFrameAnim.setOnClickListener(this);
showFrameAnimByXml();
}
// 从xml文件中获取帧动画并进行播放
private void showFrameAnimByXml() {
// 设置图像视图的图像来源为帧动画的XML定义文件
ivFrameAnim.setImageResource(R.drawable.frame_anim);
// 从图像视图对象中获取帧动画
ad_frame = (AnimationDrawable) ivFrameAnim.getDrawable();
ad_frame.start(); // 开始播放帧动画
}
@Override
public void onClick(View view) {
if (view.getId() == R.id.iv_fra--me_anim) {
if (ad_frame.isRunning()) {
// 判断帧动画是否正在播放
ad_frame.stop(); /-/ 停止播放帧动画
} else {
ad_frame-.sta0rt(); // 开始播放帧动画
}
}
}
}
GIF动画实现
Android并不能直接播放GIF动图，要想GIF动图，可以借助帧动画技术。
在Android9.0之前实现方式可以通过开源框架来实现，9.0之后出现了图像解码器ImageDecoder，搭配Animatable可以轻松实现播放GIF动图。
GifImage
public class GifImage {
public static final int STATUS_OK = 0;
public static final int STATUS_FORMAT_ERROR = 1;
private static final int STATUS_OPEN_ERROR = 2;
private int status;
private InputStream in;
private int width;
private int height;
private boolean gctFlag;
private int gctSize;
private int[] gct;
private int[] lct;
private int[] act;
private int bgIndex;
private int bgColor;
private int lastBgColor;
private boolean interlace;
private int ix, iy, iw, ih;
private int lrx, lry, lrw, lrh;
private Bitmap image;
private Bitmap lastImage;
private byte[] block = new byte[256];
private int blockSize = 0;
private int dispose = 0;
private int lastDispose = 0;
private boolean transparency = false;
private int delay = 0;
private int transIndex;
private static final int MaxStackSize = 4096;
private short[] prefix;
private byte[] suffix;
private byte[] pixelStack;
private byte[] pixels;
private Vector<GifFrame> frames;
private int frameCount;
public static class GifFrame {
public Bitmap image;
public int delay;
GifFrame(Bitmap im, int del) {
image = im;
delay = del;
}
}
public GifFrame[] getFrames() {
if (null != frames)
return frames.toArray(new GifFrame[0]);
return null;
}
public int read(InputStream is) {
init();
if (is != null) {
in = is;
readHeader();
if (!err()) {
readContents();
if (frameCount < 0) {
status = STATUS_FORMAT_ERROR;
}
}
} else {
status = STATUS_OPEN_ERROR;
}
try {
assert is != null;
is.close();
} catch (Exception e) {
e.printStackTrace();
}
return status;
}
private void setPixels() {
int[] dest = new int[width * height];
if (lastDispose > 0) {
if (lastDispose == 3) {
int n = frameCount - 2;
if (n > 0) {
lastImage = getFrame(n - 1);
} else {
lastImage = null;
}
}
if (lastImage != null) {
lastImage.getPixels(dest, 0, width, 0, 0, width, height);
if (lastDispose == 2) {
int c = 0;
if (!transparency) {
c = lastBgColor;
}
for (int i = 0; i < lrh; i++) {
int n1 = (lry + i) * width + lrx;
int n2 = n1 + lrw;
for (int k = n1; k < n2; k++) {
dest[k] = c;
}
}
}
}
}
int pass = 1;
int inc = 8;
int iline = 0;
for (int i = 0; i < ih; i++) {
int line = i;
if (interlace) {
if (iline >= ih) {
pass++;
switch (pass) {
case 2:
iline = 4;
break;
case 3:
iline = 2;
inc = 4;
break;
case 4:
iline = 1;
inc = 2;
}
}
line = iline;
iline += inc;
}
line += iy;
if (line < height) {
int k = line * width;
int dx = k + ix;
int dlim = dx + iw;
if ((k + width) < dlim) {
dlim = k + width;
}
int sx = i * iw;
while (dx < dlim) {
int index = ((int) pixels[sx++]) & 0xff;
int c = act[index];
if (c != 0) {
dest[dx] = c;
}
dx++;
}
}
}
image = Bitmap.createBitmap(dest, width, height, Config.RGB_565);
}
private Bitmap getFrame(int n) {
Bitmap im = null;
if ((n >= 0) && (n < frameCount)) {
im = frames.elementAt(n).image;
}
return im;
}
private void decodeImageData() {
int NullCode = -1;
int npix = iw * ih;
int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, count, i, datum, data_size, first, top, bi, pi;
if ((pixels == null) || (pixels.length < npix)) {
pixels = new byte[npix]; // allocate new pixel array
}
if (prefix == null) {
prefix = new short[MaxStackSize];
}
if (suffix == null) {
suffix = new byte[MaxStackSize];
}
if (pixelStack == null) {
pixelStack = new byte[MaxStackSize + 1];
}
// Initialize GIF data stream decoder.
data_size = read();
clear = 1 << data_size;
end_of_information = clear + 1;
available = clear + 2;
old_code = NullCode;
code_size = data_size + 1;
code_mask = (1 << code_size) - 1;
for (code = 0; code < clear; code++) {
prefix[code] = 0;
suffix[code] = (byte) code;
}
// Decode GIF pixel stream.
datum = bits = count = first = top = pi = bi = 0;
for (i = 0; i < npix; ) {
if (top == 0) {
if (bits < code_size) {
// Load bytes until there are enough bits for a code.
if (count == 0) {
// Read a new data block.
count = readBlock();
if (count <= 0) {
break;
}
bi = 0;
}
datum += (((int) block[bi]) & 0xff) << bits;
bits += 8;
bi++;
count--;
continue;
}
// Get the next code.
code = datum & code_mask;
datum >>= code_size;
bits -= code_size;
// Interpret the code
if ((code > available) || (code == end_of_information)) {
break;
}
if (code == clear) {
// Reset decoder.
code_size = data_size + 1;
code_mask = (1 << code_size) - 1;
available = clear + 2;
old_code = NullCode;
continue;
}
if (old_code == NullCode) {
pixelStack[top++] = suffix[code];
old_code = code;
first = code;
continue;
}
in_code = code;
if (code == available) {
pixelStack[top++] = (byte) first;
code = old_code;
}
while (code > clear) {
pixelStack[top++] = suffix[code];
code = prefix[code];
}
first = ((int) suffix[code]) & 0xff;
// Add a new string to the string table,
if (available >= MaxStackSize) {
break;
}
pixelStack[top++] = (byte) first;
prefix[available] = (short) old_code;
suffix[available] = (byte) first;
available++;
if (((available & code_mask) == 0)
&& (available < MaxStackSize)) {
code_size++;
code_mask += available;
}
old_code = in_code;
}
// Pop a pixel off the pixel stack.
top--;
pixels[pi++] = pixelStack[top];
i++;
}
for (i = pi; i < npix; i++) {
pixels[i] = 0; // clear missing pixels
}
}
private boolean err() {
return status != STATUS_OK;
}
private void init() {
status = STATUS_OK;
frameCount = 0;
frames = new Vector<>();
gct = null;
lct = null;
}
private int read() {
int curByte = 0;
try {
curByte = in.read();
} catch (Exception e) {
status = STATUS_FORMAT_ERROR;
}
return curByte;
}
private int readBlock() {
blockSize = read();
int n = 0;
if (blockSize > 0) {
try {
int count;
while (n < blockSize) {
count = in.read(block, n, blockSize - n);
if (count == -1) {
break;
}
n += count;
}
} catch (Exception e) {
e.printStackTrace();
}
if (n < blockSize) {
status = STATUS_FORMAT_ERROR;
}
}
return n;
}
private int[] readColorTable(int ncolors) {
int nbytes = 3 * ncolors;
int[] tab = null;
byte[] c = new byte[nbytes];
int n = 0;
try {
n = in.read(c);
} catch (Exception e) {
e.printStackTrace();
}
if (n < nbytes) {
status = STATUS_FORMAT_ERROR;
} else {
tab = new int[256];
int i = 0;
int j = 0;
while (i < ncolors) {
int r = ((int) c[j++]) & 0xff;
int g = ((int) c[j++]) & 0xff;
int b = ((int) c[j++]) & 0xff;
tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
}
}
return tab;
}
private void readContents() {
boolean done = false;
while (!(done || err())) {
int code = read();
switch (code) {
case 0x2C:
readImage();
break;
case 0x21:
code = read();
switch (code) {
case 0xf9:
readGraphicControlExt();
break;
case 0xff:
readBlock();
StringBuilder app = new StringBuilder();
for (int i = 0; i < 11; i++) {
app.append((char) block[i]);
}
if (app.toString().equals("NETSCAPE2.0")) {
readNetscapeExt();
} else {
skip();
}
break;
default:
skip();
}
break;
case 0x3b:
done = true;
break;
case 0x00:
break;
default:
status = STATUS_FORMAT_ERROR;
}
}
}
private void readGraphicControlExt() {
read();
int packed = read();
dispose = (packed & 0x1c) >> 2;
if (dispose == 0) {
dispose = 1;
}
transparency = (packed & 1) != 0;
delay = readShort() * 10;
transIndex = read();
read();
}
private void readHeader() {
StringBuilder id = new StringBuilder();
for (int i = 0; i < 6; i++) {
id.append((char) read());
}
if (!id.toString().toUpperCase().startsWith("GIF")) {
status = STATUS_FORMAT_ERROR;
return;
}
readLSD();
if (gctFlag && !err()) {
gct = readColorTable(gctSize);
bgColor = gct[bgIndex];
}
}
private void readImage() {
ix = readShort();
iy = readShort();
iw = readShort();
ih = readShort();
int packed = read();
boolean lctFlag = (packed & 0x80) != 0;
interlace = (packed & 0x40) != 0;
int lctSize = 2 << (packed & 7);
if (lctFlag) {
lct = readColorTable(lctSize);
act = lct;
} else {
act = gct;
if (bgIndex == transIndex) {
bgColor = 0;
}
}
int save = 0;
if (transparency) {
save = act[transIndex];
act[transIndex] = 0;
}
if (act == null) {
status = STATUS_FORMAT_ERROR;
}
if (err()) {
return;
}
decodeImageData();
skip();
if (err()) {
return;
}
frameCount++;
image = Bitmap.createBitmap(width, height, Config.RGB_565);
setPixels();
frames.addElement(new GifFrame(image, delay));
if (transparency) {
act[transIndex] = save;
}
resetFrame();
}
private void readLSD() {
width = readShort();
height = readShort();
int packed = read();
gctFlag = (packed & 0x80) != 0;
gctSize = 2 << (packed & 7);
bgIndex = read();
}
private void readNetscapeExt() {
do {
readBlock();
} while ((blockSize > 0) && !err());
}
private int readShort() {
return read() | (read() << 8);
}
private void resetFrame() {
lastDispose = dispose;
lrx = ix;
lry = iy;
lrw = iw;
lrh = ih;
lastImage = image;
lastBgColor = bgColor;
dispose = 0;
transparency = false;
delay = 0;
lct = null;
}
private void skip() {
do {
readBlock();
} while ((blockSize > 0) && !err());
}
}
public class GifActivity extends AppCompatActivity {
private ImageView iv_gif;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_gif);
// 从布局文件中获取名叫iv_gif的图像视图
iv_gif = findViewById(R.id.iv_gif);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
// 利用Android9.0新增的AnimatedImageDrawable显示GIF动画
showGifAnimationNew();
} else {
// 显示GIF动画
showGifAnimationOld();
}
}
@TargetApi(Build.VERSION_CODES.P)
private void showGifAnimationNew() {
try {
// 利用Android9.0新增的ImageDecoder读取gif图片
ImageDecoder.Source source = ImageDecoder.createSource(
getResources(), R.drawable.welcome);
// 从数据源中解码得到gif图形数据
Drawable gifDrawable = ImageDecoder.decodeDrawable(source);
// 设置图像视图的图形为gif图片
iv_gif.setImageDrawable(gifDrawable);
// 如果是动画图形，则开始播放动画
if (gifDrawable instanceof Animatable) {
((Animatable) iv_gif.getDrawable()).start();
}
} catch (Exception e) {
e.printStackTrace();
}
}
// 显示GIF动画
private void showGifAnimationOld() {
// 从资源文件welcome.gif中获取输入流对象
InputStream is = getResources().openRawResource(R.raw.welcome);
// 创建一个GIF图像对象
GifImage gifImage = new GifImage();
// 从输入流中读取gif数据
int code = gifImage.read(is);
if (code == GifImage.STATUS_OK) {
// 读取成功
GifImage.GifFrame[] frameList = gifImage.getFrames();
// 创建一个帧动画
AnimationDrawable ad_gif = new AnimationDrawable();
for (GifImage.GifFrame frame : frameList) {
// 把Bitmap位图对象转换为Drawable图形格式
BitmapDrawable bitmapDrawable = new BitmapDrawable(getResources(), frame.image);
// 给帧动画添加指定图形，以及该帧的播放延迟
ad_gif.addFrame(bitmapDrawable, frame.delay);
}
// 设置帧动画是否只播放一次。为true表示只播放一次，为false表示循环播放
ad_gif.setOneShot(false);
// 设置图像视图的图形为帧动画
iv_gif.setImageDrawable(ad_gif);
ad_gif.start(); // 开始播放帧动画
} else if (code == GifImage.STATUS_FORMAT_ERROR) {
Toast.makeText(this, "该图片不是gif格式", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(this, "gif图片读取失败:" + code, Toast.LENGTH_LONG).show();
}
}
}