新手--從網絡加載圖檔并存儲在本地,斷開網絡後依然可以顯示圖檔

MainActivity代碼:

package com.demo.save;

import android.graphics.Bitmap;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView;

import butterknife.ButterKnife;
import butterknife.InjectView;

public class MainActivity extends AppCompatActivity {

    @InjectView(R.id.imageview)
    ImageView imageview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.inject(this);

        if (Task.getDiskBitmap(Task.imagePath) == null) {
            loadImg(Task.path);
        } else {
            imageview.setImageBitmap(Task.getDiskBitmap(Task.imagePath));
        }
    }

    private void loadImg(String url) {
        Task task = new Task(new Task.ImageCallBack() {
            @Override
            public void callBitmap(Bitmap bitmap) {
                if (bitmap != null) {
                    imageview.setImageBitmap(bitmap);
                }
            }
        });
        //執行圖檔請求
        task.execute(url);
    }
}


Task 網絡擷取資料類:

       
package com.demo.save;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.Toast;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Created by yafr1hz1 on 2017/9/7.
 */

public class Task extends AsyncTask<String, Void, Bitmap> {
    public static String path = "http://139.224.104.4:8085/iknow/upload/product/1/2017/8/18/1014148680.jpg";
    private String fileName;
    public static String imagePath;

    /**
     * 定義一個圖檔的接口回調
     */
    public interface ImageCallBack {
        void callBitmap(Bitmap bitmap);
    }

    //定義變量記住調用者所傳遞進來的回調監聽對象
    private ImageCallBack imageCallBack;

    //構造方法
    public Task(ImageCallBack imageCallBack) {
        this.imageCallBack = imageCallBack;
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        try {
            String path = params[0];
            URL url = new URL(path);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(5 * 1000);
            connection.setReadTimeout(2 * 1000);
            //伺服器響應
            int code = connection.getResponseCode();
            if (code == HttpURLConnection.HTTP_OK) {
                //判斷伺服器是否連接配接成功并相應 //
                InputStream is = connection.getInputStream();
                loadImageFromNetwork(MyApplication.getContext(), path);
                //将圖檔流轉化成Bitmap位圖，傳回
                return BitmapFactory.decodeStream(is);
            }
        } catch (Exception e) {
            Log.d("網絡錯誤----", e.toString());
        }
        return null;
    }

    public void loadImageFromNetwork(Context context, String imageUrl) {
        // 擷取url中圖檔的檔案名與字尾
        if (imageUrl != null && imageUrl.length() != 0) {
            fileName = imageUrl.substring(imageUrl.lastIndexOf("/") + 1);
        }
        // 圖檔在手機本地的存放路徑,  注意：fileName為空的情況
        imagePath = context.getCacheDir() + "/" + fileName;

        File file = new File(context.getCacheDir(), fileName);
        // 儲存檔案
        if (!file.exists() && !file.isDirectory()) {
            try {
                // 可以在這裡通過檔案名來判斷，是否本地有此圖檔
                FileOutputStream fos = new FileOutputStream(file);
                InputStream is = new URL(imageUrl).openStream();
                int data = is.read();
                while (data != -1) {
                    fos.write(data);
                    data = is.read();
                }
                fos.close();
                is.close();
            } catch (IOException e) {
                Log.d("test", e.getMessage());
            }
        } else {
            Log.d("test", "file.exists()檔案存在，本地擷取");
        }
        Log.d("檔案路徑-----", imagePath);
    }

    //讀取本地圖檔 參數: 檔案路徑
    public static Bitmap getDiskBitmap(String pathString) {
        Bitmap bitmap = null;
        try {
            bitmap = BitmapFactory.decodeFile(pathString);
        } catch (Exception e) {
        }
        return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        super.onPostExecute(bitmap);
        if (fileName == null) {
            Toast.makeText(MyApplication.getContext(),"請檢查網絡狀态後重試",Toast.LENGTH_LONG).show();
        }
        if (bitmap != null) {
            //設定圖檔 回調回去
            imageCallBack.callBitmap(bitmap);
        }
    }
}      
        


Application :

       
package com.demo.save;

import android.app.Application;
import android.content.Context;

/**
 * Created by yafr1hz1 on 2017/9/7.
 */

public class MyApplication extends Application {
    private static Context context;

    @Override
    public void onCreate() {
        super.onCreate();
        context = getApplicationContext();
    }

    /**
     * 擷取全局上下文
     */
    public static Context getContext() {
        return context;
    }
}      
        
注:在manifest檔案中<application>節點下配置        
android:name="MyApplication"      
   
        
添加網絡通路權限


布局檔案: (喜歡的話可以自己添加一個button,點選button後加載圖檔,這裡是在Activity建立之後直接加載圖檔的)
       
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.demo.save.MainActivity"
    >

    <ImageView
        android:id="@+id/imageview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        />
</RelativeLayout>      
    
好了,到這裡結束了.第一篇部落格!