Android核心技術-day04-01-網路圖片檢視器(安卓訊息迴圈機制)
阿新 • • 發佈：2018-11-07
package com.gaozewen.netimageviewer; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.ImageView; import android.widget.Toast; import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.InputStream; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; import java.util.ArrayList; import java.util.List; public class MainActivity extends AppCompatActivity { private static final int LOAD_IMAGE = 1; private static final int LOAD_ERROR = 2; private ImageView iv; private List<String> paths; private int currentPosition = 0; // UIThread 主執行緒 ↓ private Handler mHandler = new Handler(new Handler.Callback() { @Override public boolean handleMessage(Message msg) { switch (msg.what){ case LOAD_IMAGE: Bitmap bitmap = (Bitmap) msg.obj; iv.setImageBitmap(bitmap); Toast.makeText(MainActivity.this,"載入圖片成功", Toast.LENGTH_SHORT).show(); break; case LOAD_ERROR: Toast.makeText(MainActivity.this,"載入圖片失敗", Toast.LENGTH_SHORT).show(); break; } return true; } }); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); iv = (ImageView) findViewById(R.id.iv); // 1.連結伺服器，獲取所有的圖片連結資訊 loadAllImagePath(); } // 獲取全部圖片資源路徑 private void loadAllImagePath() { new Thread() { @Override public void run() { // 獲取伺服器資料 try { URL url = new URL("http://192.168.1.102:8080/img/gaga.html"); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); // 注意 GET 請求必須大寫 int code = conn.getResponseCode(); if (code == 200) { // 返回成功 InputStream is = conn.getInputStream(); File file = new File(getCacheDir(), "info.txt"); FileOutputStream fos = new FileOutputStream(file); byte[] buffer = new byte[1024]; int len = 0; while ((len = is.read(buffer)) != -1) { fos.write(buffer, 0, len); } fos.flush(); fos.close(); is.close(); beginLoadImage(); } else if (code == 404) { Message msg = Message.obtain(); msg.what = LOAD_ERROR; msg.obj = "獲取html失敗，返回碼：" + code; mHandler.sendMessage(msg); }else { Message msg = Message.obtain(); msg.what = LOAD_ERROR; msg.obj = "伺服器異常，返回碼：" + code; mHandler.sendMessage(msg); } } catch (Exception e) { e.printStackTrace(); } } }.start(); } // 開始載入圖片，在從伺服器獲取完畢圖片資源路徑之後執行 private void beginLoadImage() { try { paths = new ArrayList<>(); File file = new File(getCacheDir(), "info.txt"); FileInputStream fis = new FileInputStream(file); BufferedReader br = new BufferedReader(new InputStreamReader(fis)); String line; while ((line = br.readLine()) != null) { paths.add(line); } br.close(); fis.close(); loadImageByPath(paths.get(currentPosition)); } catch (Exception e) { e.printStackTrace(); } } // private void loadImageByPath(final String path) { new Thread() { @Override public void run() { try { File file = new File(getCacheDir(), path.replace("/", "") + ".jpg"); if (file.exists() && file.length() > 0){ // 快取中有檔案 System.out.println("通過快取把圖片獲取出來..."); Message msg = Message.obtain(); msg.what = LOAD_IMAGE; msg.obj = BitmapFactory.decodeFile(file.getAbsolutePath()); mHandler.sendMessage(msg); // 安卓訊息迴圈機制 // Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath()); // iv.setImageBitmap(bitmap); /** * 建立子執行緒 訊息迴圈！！！！ */ // UIThread 被建立之後就自帶了一個 Looper， // 這個 Looper 管理自身的 MessageQueue , // 其他創建出來的子執行緒 預設沒有 Looper， // 只能呼叫 Looper.prepare 和 Looper.loop 方法來進行訊息迴圈 // 並且要 new 一個 Handler 物件來處理取出的 Message 物件 /*Looper.prepare(); mHandler = new Handler(){ @Override public void handleMessage(Message msg) { Toast.makeText(MainActivity.this,"載入圖片完成" + msg.what, Toast.LENGTH_SHORT).show(); } }; Message msg = Message.obtain(); msg.what = 100; mHandler.sendMessage(msg); Looper.loop();*/ }else { // 快取中沒檔案 System.out.println("通過訪問網路把圖片資源獲取出來..."); URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); int code = conn.getResponseCode(); if(code == 200){ InputStream is = conn.getInputStream(); // 暫存在記憶體裡的 圖片 Bitmap bitmap = BitmapFactory.decodeStream(is); // 將這個圖片寫入到 cache 資料夾中 FileOutputStream fos = new FileOutputStream(file); bitmap.compress(Bitmap.CompressFormat.JPEG,100,fos); fos.close(); is.close(); Message msg = Message.obtain(); msg.what = LOAD_IMAGE; msg.obj = BitmapFactory.decodeFile(file.getAbsolutePath()); mHandler.sendMessage(msg); }else { /*Looper.prepare(); mHandler = new Handler(){ @Override public void handleMessage(Message msg) { Toast.makeText(MainActivity.this,"獲取失敗", Toast.LENGTH_SHORT).show(); } }; Looper.loop();*/ Message msg = Message.obtain(); msg.what = LOAD_ERROR; msg.obj = "獲取圖片失敗，返回碼：" + code; mHandler.sendMessage(msg); } } } catch (Exception e) { e.printStackTrace(); Message msg = Message.obtain(); msg.what = LOAD_ERROR; msg.obj = "獲取圖片失敗,拋異常！！" ; mHandler.sendMessage(msg); } } }.start(); } public void pre(View view) { currentPosition--; if (currentPosition < 0){ currentPosition = paths.size() -1; } loadImageByPath(paths.get(currentPosition)); } public void next(View view) { currentPosition++; if (currentPosition >= paths.size()){ currentPosition = 0; } loadImageByPath(paths.get(currentPosition)); } }