通过案例快速学会Picasso图片缓存库

来源：互联网发布：网络版进销存软件编辑：程序博客网时间：2024/05/17 22:55

picasso是Square公司开源的一个Android图形缓存库，官网地址http://square.github.io/picasso/，可以实现图片下载和缓存功能。
下载地址：https://github.com/square/picasso

这里写图片描述

配置方法

MAVEN<dependency>  <groupId>com.squareup.picasso</groupId>  <artifactId>picasso</artifactId>  <version>(insert latest version)</version></dependency>

GRADLEcompile 'com.squareup.picasso:picasso:(insert latest version)'

基本使用

picasso仅需一行代码就能实现图片的异步加载

Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);

Picasso不仅实现了图片异步加载的功能，还解决了android中加载图片时需要解决的一些常见问题：

在adapter中需要取消已经不在视野范围的ImageView图片资源的加载，否则会导致图片错位，Picasso已经解决了这个问题。
使用复杂的图片压缩转换来尽可能的减少内存消耗
自带内存和硬盘二级缓存功能

Picasso特性

ADAPTER 中的下载：Adapter的重用会被自动检测到，Picasso会取消上次的加载

@Override public void getView(int position, View convertView, ViewGroup parent) {  SquaredImageView view = (SquaredImageView) convertView;  if (view == null) {    view = new SquaredImageView(context);  }  String url = getItem(position);  Picasso.with(context).load(url).into(view);}

图片转换：转换图片以适应布局大小并减少内存占用

Picasso.with(context)  .load(url)  .resize(50, 50)  .centerCrop()  .into(imageView)

你还可以自定义转换：

public class CropSquareTransformation implements Transformation {  @Override public Bitmap transform(Bitmap source) {    int size = Math.min(source.getWidth(), source.getHeight());    int x = (source.getWidth() - size) / 2;    int y = (source.getHeight() - size) / 2;    Bitmap result = Bitmap.createBitmap(source, x, y, size, size);    if (result != source) {      source.recycle();    }    return result;  }  @Override public String key() { return "square()"; }}

将CropSquareTransformation 的对象传递给transform 方法即可。

Place holders-空白或者错误占位图片
picasso提供了两种占位图片，未加载完成或者加载发生错误的时需要一张图片作为提示。

Picasso.with(context)    .load(url)    .placeholder(R.drawable.user_placeholder)//没有加载图片时显示的默认图像    .error(R.drawable.user_placeholder_error)// 图像加载错误时显示的图像    .into(imageView);// 被加载的控件

如果加载发生错误会重复三次请求，三次都失败才会显示erro Place holder。
资源文件的加载
除了加载网络图片以外，picasso还支持加载Resources, assets, files, content providers中的资源文件。

Picasso.with(context).load(R.drawable.landing_screen).into(imageView1);Picasso.with(context).load("file:///android_asset/DvpvklR.png").into(imageView2);Picasso.with(context).load(new File(...)).into(imageView3);

列表使用Picasso加载图片案例

这里写图片描述

首先在dependencies 中添加Picasso相关配置

compile ‘com.squareup.picasso:picasso:2.5.2’

然后上源码：

ListViewActivity.java

import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.widget.ListView;import java.util.ArrayList;import java.util.List;/** * Created by huangshuai on 2016/5/20. * Email：huangshuai@wooyun.org * 列表Activity */public class ListViewActivity extends AppCompatActivity {    private ListView lv_main;    private List<SunBean> listDatas;    private SunAdapter lAdapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.list_view);        lv_main = (ListView) findViewById(R.id.list_sun);        listDatas = new ArrayList<>();        initData();        lAdapter = new SunAdapter(listDatas, this);        lv_main.setAdapter(lAdapter);    }    /**     * 初始化数据     */    private void initData() {        SunBean sun1 = new SunBean();        sun1.setTitle("太阳的后裔一");        sun1.setPicUrl("http://img3.imgtn.bdimg.com/it/u=3746050745,4184822198&fm=11&gp=0.jpg");        listDatas.add(sun1);        SunBean sun2 = new SunBean();        sun2.setTitle("太阳的后裔二");        sun2.setPicUrl("http://cdn.duitang.com/uploads/item/201603/02/20160302223503_jmdXT.thumb.224_0.jpeg");        listDatas.add(sun2);        SunBean news3 = new SunBean();        news3.setTitle("太阳的后裔三");        news3.setPicUrl("http://img5.duitang.com/uploads/item/201602/23/20160223132131_RNSQ3.thumb.224_0.jpeg");        listDatas.add(news3);        SunBean sun4 = new SunBean();        sun4.setTitle("太阳的后裔四");        sun4.setPicUrl("http://img5.duitang.com/uploads/item/201603/03/20160303163634_iveUE.thumb.224_0.jpeg");        listDatas.add(sun4);        SunBean sun5 = new SunBean();        sun5.setTitle("太阳的后裔五");        sun5.setPicUrl("http://cdn.duitang.com/uploads/item/201603/07/20160307013640_FQCTc.thumb.224_0.jpeg");        listDatas.add(sun5);        SunBean sun6 = new SunBean();        sun6.setTitle("太阳的后裔六");        sun6.setPicUrl("http://img4.duitang.com/uploads/item/201603/03/20160303102359_vzwPC.thumb.224_0.jpeg");        listDatas.add(sun6);        SunBean news7 = new SunBean();        news7.setTitle("太阳的后裔七");        news7.setPicUrl("http://img4.duitang.com/uploads/item/201603/03/20160303101132_AMPRv.thumb.224_0.jpeg");        listDatas.add(news7);        SunBean sun8 = new SunBean();        sun8.setTitle("太阳的后裔八");        sun8.setPicUrl("http://img0.imgtn.bdimg.com/it/u=1043934750,464206674&fm=11&gp=0.jpg");        listDatas.add(sun8);    }}

SunAdapter.java

import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.TextView;import com.squareup.picasso.Picasso;import java.util.List;/** * Created by huangshuai on 2016/5/20. * Email：huangshuai@wooyun.org * 列表Adapter */public class SunAdapter extends BaseAdapter {    private List<SunBean> list_sun;    private LayoutInflater inflater;    private Context context;    public SunAdapter(List<SunBean> list_new, Context context) {        this.list_sun = list_new;        this.context = context;        this.inflater = LayoutInflater.from(context);    }    @Override    public int getCount() {        return list_sun.size();    }    @Override    public Object getItem(int position) {        return list_sun.get(position);    }    @Override    public long getItemId(int position) {        return position;    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        ItemViewHodler viewHolder;        if (convertView == null) {            viewHolder = new ItemViewHodler();            convertView = inflater.inflate(R.layout.list_item, null);            viewHolder.title = (TextView) convertView.findViewById(R.id.item_title);            viewHolder.pic = (ImageView) convertView.findViewById(R.id.item_pic);            convertView.setTag(viewHolder);        } else {            viewHolder = (ItemViewHodler) convertView.getTag();        }        viewHolder.title.setText(list_sun.get(position).getTitle());        Picasso.with(context).load(list_sun.get(position).getPicUrl()).fit()                .placeholder(R.mipmap.alibg)                .error(R.mipmap.ic_launcher)                .into(viewHolder.pic);        return convertView;    }    class ItemViewHodler {        TextView title;        ImageView pic;    }}

SunBean.java

/** * Created by huangshuai on 2016/5/20. * Email：huangshuai@wooyun.org * 列表图片Bean */public class SunBean {    private String title;    private String picUrl;    public SunBean(String title, String picUrl) {        this.title = title;        this.picUrl = picUrl;    }    public SunBean() {    }    public String getTitle() {        return title;    }    public void setTitle(String title) {        this.title = title;    }    public String getPicUrl() {        return picUrl;    }    public void setPicUrl(String picUrl) {        this.picUrl = picUrl;    }}

list_itmxml

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent">    <TextView        android:id="@+id/item_title"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_centerHorizontal="true"        android:text="太阳的后裔" />    <ImageView        android:id="@+id/item_pic"        android:layout_width="160dp"        android:layout_height="240dp"        android:layout_centerHorizontal="true"        android:layout_below="@id/item_title"        android:src="@mipmap/alibg" /></RelativeLayout>

list_view.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent">    <ListView        android:id="@+id/list_sun"        android:layout_width="match_parent"        android:layout_height="match_parent"></ListView></RelativeLayout>

最后不要忘了增加网络权限

<uses-permission android:name="android.permission.INTERNET" />

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