优雅地实现Android主流图片加载框架封装,可无侵入切换框架
项目开发中,往往会随着需求的改变而切换到其它图片加载框架上去。如果最初代码设计的耦合度太高,那么恭喜你,成功入坑了。至今无法忘却整个项目一行行去复制粘贴被支配的恐惧。:)
那么是否存在一种方式 能够一劳永逸地解决这个痛点呢?下面我们来分析一下图片加载框架面对的现状和解决思路。
私信【Android有福利领取】
问题现状
一个优秀的框架一般在代码设计的时候已经封装很不错了,对于开发者而言框架的使用也是很方便,但是为什么说我们往往还要去做这方面的框架封装呢?原因很简单,实际项目开发中,我们不得不面对着日新月异的需求变化,想要在这个变化中最大程度的实现代码的可扩展性和变通性(当然还可以偷懒),不能因为牵一发而动全身,同时要将框架适配到实际项目,框架的再封装设计显得尤为重要。
不多废话,我们可以开始今天的图片封装之路了。
设计思路
图片框架的封装主要需要满足以下三点:
-
低耦合,方便将来的代码扩展。至少要支持目前市场上使用率最高的图片框架Fresco、Glide、Picasso三者之间的切换
-
满足项目中各种需求
-
调用方便
谈到图片封装,最先想到的是把一些常用的功能点作为参数传入到方法内,然后调用图片加载框架实现我们图片的加载工作。比如说像下面这样
public interface ImageLoader {
void loadImage(ImageView view, String path, int placeholderId, int errorId,boolean skipMemory);
void loadImage(ImageView view, File file, int placeholderId, int errorId, boolean skipMemory);
}
然后分别写对应的ImageLoader实现类FrescoImageLoader、GlideImageLoader、PicassoImageLoader,最后采用策略的设计模式实现代码的切换。那么这种方式实际效果如何呢?实际开发中很明显的一个 问题就是,对于每一个需要的参数都需要进行对应的封装,就不止上面所提到的两个方法,我们需要封装大量的方法去满足实际的项目需要,而且每个框架的很多属性不一致,如果切换图片框架的话,还是需要大量的切换成本的。
于是我们想到了下面的这种思路
public interface ILoaderStrategy {
void loadImage(LoaderOptions options);
/**
* 清理内存缓存
*/
void clearMemoryCache();
/**
* 清理磁盘缓存
*/
void clearDiskCache();
}
提取各个框架通用的View,path/file文件路径,通过LoaderOptions解决大量不同参数传入的问题。这里需要说明的是,LoaderOptions中采用控件View,而不是ImageView,主要考虑到Fresco图片框架采用了DraweeView,这里保留了设计的扩展性。而图片参数类LoaderOptions采用了Builder设计模式:
public class LoaderOptions {
public int placeholderResId;
public int errorResId;
public boolean isCenterCrop;
public boolean isCenterInside;
public boolean skipLocalCache; //是否缓存到本地
public boolean skipNetCache;
public Bitmap.Config config = Bitmap.Config.RGB_565;
public int targetWidth;
public int targetHeight;
public float bitmapAngle; //圆角角度
public float degrees; //旋转角度.注意:picasso针对三星等本地图片,默认旋转回0度,即正常位置。此时不需要自己rotate
public Drawable placeholder;
public View targetView;//targetView展示图片
public BitmapCallBack callBack;
public String url;
public File file;
public int drawableResId;
public Uri uri;
public LoaderOptions(String url) {
this.url = url;
}
public LoaderOptions(File file) {
this.file = file;
}
public LoaderOptions(int drawableResId) {
this.drawableResId = drawableResId;
}
public LoaderOptions(Uri uri) {
this.uri = uri;
}
public void into(View targetView) {
this.targetView = targetView;
ImageLoader.getInstance().loadOptions(this);
}
public void bitmap(BitmapCallBack callBack) {
this.callBack = callBack;
ImageLoader.getInstance().loadOptions(this);
}
public LoaderOptions placeholder(@DrawableRes int placeholderResId) {
this.placeholderResId = placeholderResId;
return this;
}
public LoaderOptions placeholder(Drawable placeholder) {
this.placeholder = placeholder;
return this;
}
public LoaderOptions error(@DrawableRes int errorResId) {
this.errorResId = errorResId;
return this;
}
public LoaderOptions centerCrop() {
isCenterCrop = true;
return this;
}
public LoaderOptions centerInside() {
isCenterInside = true;
return this;
}
public LoaderOptions config(Bitmap.Config config) {
this.config = config;
return this;
}
public LoaderOptions resize(int targetWidth, int targetHeight) {
this.targetWidth = targetWidth;
this.targetHeight = targetHeight;
return this;
}
/**
* 圆角
* @param bitmapAngle 度数
* @return
*/
public LoaderOptions angle(float bitmapAngle) {
this.bitmapAngle = bitmapAngle;
return this;
}
public LoaderOptions skipLocalCache(boolean skipLocalCache) {
this.skipLocalCache = skipLocalCache;
return this;
}
public LoaderOptions skipNetCache(boolean skipNetCache) {
this.skipNetCache = skipNetCache;
return this;
}
public LoaderOptions rotate(float degrees) {
this.degrees = degrees;
return this;
}
}
当然了,如果觉得有项目中需要可以以LoderOptions为基类继续扩展LoderOptions,不过现在这样在LoaderOptions上自行扩展基本上可以满足所有日常需要了。现在解决了代码设计的方向,那么接下来 我们要采取策略的方式实现图片框架的解耦。
import android.view.View;
import com.squareup.picasso.Callback;
import java.io.File;
/**
* 图片管理类,提供对外接口。
* 静态代理模式,开发者只需要关心ImageLoader + LoaderOptions
* Created by MhListener on 2017/6/27.
*/
public class ImageLoader{
private static ILoaderStrategy sLoader;
private static volatile ImageLoader sInstance;
private ImageLoader() {
}
//单例模式
public static ImageLoader getInstance() {
if (sInstance == null) {
synchronized (ImageLoader.class) {
if (sInstance == null) {
//若切换其它图片加载框架,可以实现一键替换
sInstance = new ImageLoader();
}
}
}
return sInstance;
}
//提供实时替换图片加载框架的接口
public void setImageLoader(ILoaderStrategy loader) {
if (loader != null) {
sLoader = loader;
}
}
public LoaderOptions load(String path) {
return new LoaderOptions(path);
}
public LoaderOptions load(int drawable) {
return new LoaderOptions(drawable);
}
public LoaderOptions load(File file) {
return new LoaderOptions(file);
}
public LoaderOptions load(Uri uri) {
return new LoaderOptions(uri);
}
public void loadOptions(LoaderOptions options) {
sLoader.loadImage(options);
}
public void clearMemoryCache() {
sLoader.clearMemoryCache();
}
public void clearDiskCache() {
sLoader.clearDiskCache();
}
}
最后我们开始图片加载框架的具体实现方式,这里我实现了Picasso图片加载,开发者可以根据此例自行扩展GlideLoader或者FrescoLoader。
public class PicassoLoader implements ILoaderStrategy {
private volatile static Picasso sPicassoSingleton;
private final String PICASSO_CACHE = "picasso-cache";
private static LruCache sLruCache = new LruCache(App.gApp);
private static Picasso getPicasso() {
if (sPicassoSingleton == null) {
synchronized (PicassoLoader.class) {
if (sPicassoSingleton == null) {
sPicassoSingleton = new Picasso.Builder(App.gApp).memoryCache(sLruCache).build();
}
}
}
return sPicassoSingleton;
}
@Override
public void clearMemoryCache() {
sLruCache.clear();
}
@Override
public void clearDiskCache() {
File diskFile = new File(App.gApp.getCacheDir(), PICASSO_CACHE);
if (diskFile.exists()) {
//这边自行写删除代码
// FileUtil.deleteFile(diskFile);
}
}
@Override
public void loadImage(LoaderOptions options) {
RequestCreator requestCreator = null;
if (options.url != null) {
requestCreator = getPicasso().load(options.url);
} else if (options.file != null) {
requestCreator = getPicasso().load(options.file);
}else if (options.drawableResId != 0) {
requestCreator = getPicasso().load(options.drawableResId);
} else if (options.uri != null){
requestCreator = getPicasso().load(options.uri);
}
if (requestCreator == null) {
throw new NullPointerException("requestCreator must not be null");
}
if (options.targetHeight > 0 && options.targetWidth > 0) {
requestCreator.resize(options.targetWidth, options.targetHeight);
}
if (options.isCenterInside) {
requestCreator.centerInside();
} else if (options.isCenterCrop) {
requestCreator.centerCrop();
}
if (options.config != null) {
requestCreator.config(options.config);
}
if (options.errorResId != 0) {
requestCreator.error(options.errorResId);
}
if (options.placeholderResId != 0) {
requestCreator.placeholder(options.placeholderResId);
}
if (options.bitmapAngle != 0) {
requestCreator.transform(new PicassoTransformation(options.bitmapAngle));
}
if (options.skipLocalCache) {
requestCreator.memoryPolicy(MemoryPolicy.NO_CACHE, MemoryPolicy.NO_STORE);
}
if (options.skipNetCache) {
requestCreator.networkPolicy(NetworkPolicy.NO_CACHE, NetworkPolicy.NO_STORE);
}
if (options.degrees != 0) {
requestCreator.rotate(options.degrees);
}
if (options.targetView instanceof ImageView) {
requestCreator.into(((ImageView)options.targetView));
} else if (options.callBack != null){
requestCreator.into(new PicassoTarget(options.callBack));
}
}
class PicassoTarget implements Target {
BitmapCallBack callBack;
protected PicassoTarget(BitmapCallBack callBack) {
this.callBack = callBack;
}
@Override
public void onBitmapLoaded(Bitmap bitmap, Picasso.LoadedFrom from) {
if (this.callBack != null) {
this.callBack.onBitmapLoaded(bitmap);
}
}
@Override
public void onBitmapFailed(Exception e, Drawable errorDrawable) {
if (this.callBack != null) {
this.callBack.onBitmapFailed(e);
}
}
@Override
public void onPrepareLoad(Drawable placeHolderDrawable) {
}
}
class PicassoTransformation implements Transformation {
private float bitmapAngle;
protected PicassoTransformation(float corner){
this.bitmapAngle = corner;
}
@Override
public Bitmap transform(Bitmap source) {
float roundPx = bitmapAngle;//圆角的横向半径和纵向半径
Bitmap output = Bitmap.createBitmap(source.getWidth(),
source.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(output);
final int color = 0xff424242;
final Paint paint = new Paint();
final Rect rect = new Rect(0, 0, source.getWidth(),source.getHeight());
final RectF rectF = new RectF(rect);
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(source, rect, rect, paint);
source.recycle();
return output;
}
@Override
public String key() {
return "bitmapAngle()";
}
}
}
好了,到了这里,关于图片框架的封装已经全部完成。而且该图片框架的封装已经成功应用到公司项目上,目前反馈良好。如有问题,欢迎交流指教!
如果有考虑引用该封装的话,可以采用下面的方式:
//根目录下build.gradle配置
allprojects {
repositories {
...
maven { url 'https://jitpack.io' }
}
}
//项目build.gradle依赖
dependencies {
compile 'com.github.mhlistener:ImageLoader:1.0.5'
}
//使用方式
1.Application中全局设置
ImageLoader.getInstance().setGlobalImageLoader(new PicassoLoader());
2.界面中使用封装
ImageView imageView = findViewById(R.id.imageview);
String url = "http://ww2.sinaimg.cn/large/7a8aed7bgw1eutsd0pgiwj20go0p0djn.jpg";
ImageLoader.getInstance()
.load(url)
.angle(80)
.resize(400, 600)
.centerCrop()
.config(Bitmap.Config.RGB_565)
.placeholder(R.mipmap.test)
.error(R.mipmap.test)
.skipLocalCache(true)
.into(imageView);