安卓自定义View实现加载gif图片

拓拔德馨
2023-12-01

     开题:加载GIF的场景在安卓开发中还比较常见,网上也有一些三方法的框架会支持对gif的加载,在上篇博客为大家推荐的图片加载库Glide也支持gif的加载Glide工具类的简单封装,今天给大家分享通过自定义View的方式加载GIf,通过此方式,避免了在java代码中对资源图片的操作,降低了代码的关注度,只需要把被加载的Gif资源文件在xml中声明即可。

我采用的实现方式是Android自带的类 android.graphics.Movie 来加载播放Gif动画也就是把Gif资源当成Movie来处理,按来源分别可以从Gif文件的输入流,文件路径,字节数组中得到Movie的实列,然后我们可以通过操作Movie对象来操作Gif文件。


一、实现分析:

1.以Movie的形式引入Gif资源文件

引入Movie资源的方法签名:

1.Movie decodeStream(InputStream is)
2.Movie decodeFile(String pathName)
3.Movie decodeByteArray(byte[] data, int offset,int length)


1.)我使用的是字节流的方式读入声明在xml引入的gif资源:操作如下

final TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.GifView);
        mGifId = array.getResourceId(R.styleable.GifView_gif, -1);
        mPaused = array.getBoolean(R.styleable.GifView_paused, false);
        array.recycle();
        if (mGifId != -1) {
            byte[] bytes = getGiftBytes();
            mMovie = Movie.decodeByteArray(bytes, 0, bytes.length);
        }


2.) 以java代码的方式引入

    /**
     * 设置gif图资源
     *
     * @param giftResId
     */
    public void setMovieResource(int giftResId) {
        this.mGifId = giftResId;
        byte[] bytes = getGiftBytes();
        mMovie = Movie.decodeByteArray(bytes, 0, bytes.length);
        requestLayout();
    }

上述两种方式中把Gif转成byte的方法如下:

 /**
     * 将gif图片转换成byte[]
     *
     * @return byte[]
     */
    private byte[] getGiftBytes() {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        InputStream is = getResources().openRawResource(mGifId);
        byte[] b = new byte[1024];
        int len;
        try {
            while ((len = is.read(b, 0, 1024)) != -1) {
                baos.write(b, 0, len);
            }
            baos.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return baos.toByteArray();
    }

2.下面就是通过onDraw方法中不断的去通知更新Movie的当前帧,然后重绘界面

@Override
    protected void onDraw(Canvas canvas) {
        if (mMovie != null) {
            if (!mPaused) {
                updateAnimationTime();
                drawMovieFrame(canvas);
                invalidateView();
            } else {
                drawMovieFrame(canvas);
            }
        }
    }

附:这里简单提下,movie对象给我们封装了一个int 类型的duration()方法,调用该方法我们可以获得动画的总时长,

/**
     * 更新当前显示进度
     */
    private void updateAnimationTime() {
        long now = android.os.SystemClock.uptimeMillis();
        // 如果第一帧,记录起始时间
        if (mMovieStart == 0) {
            mMovieStart = now;
        }
        // 取出动画的时长
        int dur = mMovie.duration();
        if (dur == 0) {
            dur = DEFAULT_MOVIE_DURATION;
        }
        // 算出需要显示第几帧
        mCurrentAnimationTime = (int) ((now - mMovieStart) % dur);
    }

3.总结:通过以上核心实现分析,我们大概明白其实利用Movie加载GIf的流程为:

              引入Gif资源===》把gif转成byte===》利用Movie对象提供的方法计算出gif的时长===》通过onDraw不断的把更新之后的当前帧绘制出来。


二、完整实例

     1.java代码部分

/**
 * desc:利用Movie加载gif
 * author:xiedong
 * date:2017/11/21
 */
public class GifView extends View {

    /**
     * gif动态效果总时长,在未设置时长时默认为1秒
     */
    private static final int DEFAULT_MOVIE_DURATION = 1000;
    /**
     * gif图片资源ID
     */
    private int mGifId;
    /**
     * Movie实例,用来显示gift图片
     */
    private Movie mMovie;
    /**
     * 显示gift图片的动态效果的开始时间
     */
    private long mMovieStart;
    /**
     * 动态图当前显示第几帧
     */
    private int mCurrentAnimationTime = 0;
    /**
     * 图片离屏幕左边的距离
     */
    private float mLeft;
    /**
     * 图片离屏幕上边的距离
     */
    private float mTop;
    /**
     * 图片的缩放比例
     */
    private float mScale;
    /**
     * 图片在屏幕上显示的宽度
     */
    private int mMeasuredMovieWidth;
    /**
     * 图片在屏幕上显示的高度
     */
    private int mMeasuredMovieHeight;
    /**
     * 是否显示动画,为true表示显示,false表示不显示
     */
    private boolean mVisible = true;
    /**
     * 动画效果是否被暂停
     */
    private volatile boolean mPaused = false;

    public GifView(Context context) {
        this(context, null);
    }

    public GifView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public GifView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setViewAttributes(context, attrs, defStyleAttr);
    }

    /**
     * @param context  上下文
     * @param attrs    自定义属性
     * @param defStyle 默认风格
     */
    @SuppressLint("NewApi")
    private void setViewAttributes(Context context, AttributeSet attrs,
                                   int defStyle) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        }

        final TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.GifView);
        mGifId = array.getResourceId(R.styleable.GifView_gif, -1);
        mPaused = array.getBoolean(R.styleable.GifView_paused, false);
        array.recycle();
        if (mGifId != -1) {
            byte[] bytes = getGiftBytes();
            mMovie = Movie.decodeByteArray(bytes, 0, bytes.length);
        }
    }

    /**
     * 设置gif图资源
     *
     * @param giftResId
     */
    public void setMovieResource(int giftResId) {
        this.mGifId = giftResId;
        byte[] bytes = getGiftBytes();
        mMovie = Movie.decodeByteArray(bytes, 0, bytes.length);
        requestLayout();
    }

    /**
     * 手动设置 Movie对象
     *
     * @param movie Movie
     */
    public void setMovie(Movie movie) {
        this.mMovie = movie;
        requestLayout();
    }

    /**
     * 得到Movie对象
     *
     * @return Movie
     */
    public Movie getMovie() {
        return mMovie;
    }

    /**
     * 设置要显示第几帧动画
     *
     * @param time
     */
    public void setMovieTime(int time) {
        mCurrentAnimationTime = time;
        invalidate();
    }

    /**
     * 设置暂停
     *
     * @param paused
     */
    public void setPaused(boolean paused) {
        this.mPaused = paused;
        if (!paused) {
            mMovieStart = android.os.SystemClock.uptimeMillis()
                    - mCurrentAnimationTime;
        }
        invalidate();
    }

    /**
     * 判断gif图是否停止了
     *
     * @return
     */
    public boolean isPaused() {
        return this.mPaused;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (mMovie != null) {
            int movieWidth = mMovie.width();
            int movieHeight = mMovie.height();
            int maximumWidth = MeasureSpec.getSize(widthMeasureSpec);
            float scaleW = (float) movieWidth / (float) maximumWidth;
            mScale = 1f / scaleW;
            mMeasuredMovieWidth = maximumWidth;
            mMeasuredMovieHeight = (int) (movieHeight * mScale);
            setMeasuredDimension(mMeasuredMovieWidth, mMeasuredMovieHeight);
        } else {
            setMeasuredDimension(getSuggestedMinimumWidth(),
                    getSuggestedMinimumHeight());
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        mLeft = (getWidth() - mMeasuredMovieWidth) / 2f;
        mTop = (getHeight() - mMeasuredMovieHeight) / 2f;
        mVisible = getVisibility() == View.VISIBLE;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (mMovie != null) {
            if (!mPaused) {
                updateAnimationTime();
                drawMovieFrame(canvas);
                invalidateView();
            } else {
                drawMovieFrame(canvas);
            }
        }
    }

    /**
     * 重绘
     */
    @SuppressLint("NewApi")
    private void invalidateView() {
        if (mVisible) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                postInvalidateOnAnimation();
            } else {
                invalidate();
            }
        }
    }

    /**
     * 更新当前显示进度
     */
    private void updateAnimationTime() {
        long now = android.os.SystemClock.uptimeMillis();
        // 如果第一帧,记录起始时间
        if (mMovieStart == 0) {
            mMovieStart = now;
        }
        // 取出动画的时长
        int dur = mMovie.duration();
        if (dur == 0) {
            dur = DEFAULT_MOVIE_DURATION;
        }
        // 算出需要显示第几帧
        mCurrentAnimationTime = (int) ((now - mMovieStart) % dur);
    }

    /**
     * 绘制图片
     *
     * @param canvas 画布
     */
    private void drawMovieFrame(Canvas canvas) {
        // 设置要显示的帧,绘制即可
        mMovie.setTime(mCurrentAnimationTime);
        canvas.save(Canvas.MATRIX_SAVE_FLAG);
        canvas.scale(mScale, mScale);
        mMovie.draw(canvas, mLeft / mScale, mTop / mScale);
        canvas.restore();
    }

    @SuppressLint("NewApi")
    @Override
    public void onScreenStateChanged(int screenState) {
        super.onScreenStateChanged(screenState);
        mVisible = screenState == SCREEN_STATE_ON;
        invalidateView();
    }

    @SuppressLint("NewApi")
    @Override
    protected void onVisibilityChanged(View changedView, int visibility) {
        super.onVisibilityChanged(changedView, visibility);
        mVisible = visibility == View.VISIBLE;
        invalidateView();
    }

    @Override
    protected void onWindowVisibilityChanged(int visibility) {
        super.onWindowVisibilityChanged(visibility);
        mVisible = visibility == View.VISIBLE;
        invalidateView();
    }

    /**
     * 将gif图片转换成byte[]
     *
     * @return byte[]
     */
    private byte[] getGiftBytes() {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        InputStream is = getResources().openRawResource(mGifId);
        byte[] b = new byte[1024];
        int len;
        try {
            while ((len = is.read(b, 0, 1024)) != -1) {
                baos.write(b, 0, len);
            }
            baos.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return baos.toByteArray();
    }
}


2.xml中声明使用:

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.zhuandian.gif.MainActivity">

    <com.zhuandian.gifview.GifView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:gif="@mipmap/leaf" />

</android.support.constraint.ConstraintLayout>


最后附上我为大家抽成library的github引用传送门,方便大家直接以gradle的方式引入到项目中:安卓自定义View实现Gif加载

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