Android开发之利用Movie类显示GIF动画
在应用程序开发中，人机交互很重要，往往在应用中加入一个小动画，就能够让你的应用程序显得更加生动而不乏味。现在我们来列举一个实例，如何在安卓手机中显示GIF动画图片。
这个实例主要用的是android中的android.，这是android提供给我们的一个非常方便的工具。
首先，重写控件View,自定义一个展示gif图的GifView，代码如下：
[java]
package net.myprojexc.gif.view;
import net.myprojexc.gif.R;
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Movie;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;
public class GifView extends View {
/**
* 默认为1秒
*/
private static final int DEFAULT_MOVIE_DURATION = 1000;
private int mMovieResourceId;
private Movie mMovie;
private long mMovieStart;
private int mCurrentAnimationTime = 0;
private float mLeft;
private float mTop;
private float mScale;
private int mMeasuredMovieWidth;
private int mMeasuredMovieHeight;
private boolean mVisible = true;
private volatile boolean mPaused = false;
public GifView(Context context) {
this(context, null);
}
public GifView(Context context, AttributeSet attrs) {
this(context, attrs, R.styleable.CustomTheme_gifViewStyle);
}
public GifView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setViewAttributes(context, attrs, defStyle);
}
@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);
}
// 从描述文件中读出gif的值，创建出Movie实例
final TypedArray array = context.obtainStyledAttributes(attrs,
R.styleable.GifView, defStyle, R.style.Widget_GifView);
mMovieResourceId = array.getResourceId(R.styleable.GifView_gif, -1);
mPaused = array.getBoolean(R.styleable.GifView_paused, false);
array.recycle();
if (mMovieResourceId != -1) {
mMovie = Movie.decodeStream(getResources().openRawResource(
mMovieResourceId));
}
}
/**
* 设置gif图资源
*
* @param movieResId
*/
public void setMovieResource(int movieResId) {
this.mMovieResourceId = movieResId;
mMovie = Movie.decodeStream(getResources().openRawResource(
mMovieResourceId));
requestLayout();
}
public void setMovie(Movie movie) {
this.mMovie = movie;
requestLayout();
}
public Movie getMovie() {
return mMovie;
}
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);
}
}
}
@SuppressLint("NewApi")
private void invalidateView() {
if (mVisible) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
postInvalidateOnAnimation();
} else {
invalidate();
}
}
}
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);
}
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();
}
}
Movie其实管理着GIF动画中的多个帧，只需要通过 setTime() 一下就可以让它在draw()的时候绘出相应的那帧图
像。通过当前时间与duration之间的换算关系，是很容易实现GIF动起来的效果。
其次，在xml布局文件中，把这个view定义进去，代码如下：
[html]
<?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:orientation="vertical" >
<net.myprojexc.gif.view.GifView
android:id="@+id/gif1"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_gravity="center_horizontal"
android:enabled="false" />
<net.myprojexc.gif.view.GifView
android:id="@+id/gif2"
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_gravity="center_horizontal"
android:enabled="false" />
</LinearLayout>
最后，在MainActivity中的使用，代码如下：
[java]
package net.myprojexc.gif;
import net.myprojexc.gif.view.GifView;
import android.app.Activity;
import android.os.Bundle;
public class Gif extends Activity {
private GifView gif1, gif2;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
gif1 = (GifView) findViewById(R.id.gif1);
// 设置背景gif图片资源
gif1.setMovieResource(R.raw.kitty);
gif2 = (GifView) findViewById(R.id.gif2);
gif2.setMovieResource(R.raw.b);
// 设置暂停
// gif2.setPaused(true);
}
}
注意：与ImageView和其他View唯一的区别在于加了一个gif属性。
[html]
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="GifView">
<attr name="gif" format="reference" />
<attr name="paused" format="boolean" />
</declare-styleable>
<declare-styleable name="CustomTheme">
<attr name="gifViewStyle" format="reference" /> </declare-styleable>
</resources>