安卓開發-加載圖片

加載網絡上的圖片需要在manifest中配置訪問網絡的權限，如下：

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

如果不配置這個權限的話，會報錯：unknown host exception。

package com.example.loadimgfromweb;

import java.io.InputStream;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.widget.ImageView;

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		ImageView v = (ImageView) findViewById(R.id.imageView1);
		String url = "http://minimg.hexun.com/i1.hexunimg.cn/2011-11-07/134970028_200x150.jpg";
		new DownLoadImage(v).execute(url);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}

	public class DownLoadImage extends AsyncTask<String, Void, Bitmap> {
		ImageView imageView;

		public DownLoadImage(ImageView imageView) {
			this.imageView = imageView;
		}

		@Override
		protected Bitmap doInBackground(String... urls) {
			String url = urls[0];
			Bitmap tmpBitmap = null;
			try {
				InputStream is = new java.net.URL(url).openStream();
				tmpBitmap = BitmapFactory.decodeStream(is);
			} catch (Exception e) {
				e.printStackTrace();
			}
			return tmpBitmap;
		}

		@Override
		protected void onPostExecute(Bitmap result) {
			imageView.setImageBitmap(result);
		}
	}
}

上面的例子中使用了AsyncTask來與前端用戶界面進行交互。避免加載時間過長，影響界面的交互性。

如果是加載本地圖片的話，直接來：

ImageView v = (ImageView) findViewById(R.id.imageView1);
		v.setImageResource(R.drawable.apic);

------------------------

在使用AsyncTask加載圖片的時候可以順便把圖片保存在本地：

 

@Override
		protected Bitmap doInBackground(String... urls) {
			String url = urls[0];
			Bitmap tmpBitmap = null;
			try {
				InputStream is = new java.net.URL(url).openStream();
				URL u = new URL(url);
				HttpURLConnection conn = (HttpURLConnection) u.openConnection();
				Bitmap bitmap = BitmapFactory.decodeStream(is);
				// 判斷是否有內存卡
				if (Environment.getExternalStorageState().equals(
						Environment.MEDIA_MOUNTED)) {

					// 保存圖片到本地
					File sdCardDir = Environment.getExternalStorageDirectory();
					String fileName = "a.jpg";
					String filePath = sdCardDir + "/" + fileName;
					FileOutputStream fos = new FileOutputStream(filePath);
					bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);

				}
				// 關閉流
				is.close();
				conn.disconnect();

				return bitmap;
			} catch (Exception e) {
				e.printStackTrace();
			}
			return tmpBitmap;
		}