Android AsyncTask

AsyncTaskActivity

package org.wp.activity;

import java.io.InputStream;
import java.text.DecimalFormat;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Bitmap.Config;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class AsyncTaskActivity extends Activity {
	/** Context对象 **/
	private Context mContext;
	/** 开始加载图片 **/
	private Button myButton;
	/** 显示加载进度 **/
	private TextView myTextView;
	/** 加载图片开始时间 **/
	private Long mLoadStartTime = 0L;
	/** 加载图片结束时间 **/
	private Long mLoadEndTime = 0L;
	/** 格式化对象 **/
	private DecimalFormat decf;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.asynctask);
		mContext = this;
		decf = new DecimalFormat("0.00");

		myTextView = (TextView) this.findViewById(R.id.myTextView);
		myButton = (Button) this.findViewById(R.id.myButton);
		myButton.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				loadImage();
			}
		});
	}

	private void loadImage() {
		/**
		 * AsyncTask 定义了三种泛型类型 Params，Progress和Result。
		 * Params 启动任务执行的输入参数，比如HTTP请求的URL。 
		 * Progress 后台任务执行的百分比。 
		 * Result 后台执行任务最终返回的结果，比如String。
		 */
		new AsyncTask<Void, Double, Long>() {
			@Override
			protected void onPreExecute() {
				myTextView.setText("开始加载图片");
			}

			@Override
			protected Long doInBackground(Void... params) {
				mLoadStartTime = System.currentTimeMillis();

				for (int i = 0; i < 2000; i++) {
					readBitmap(mContext, R.drawable.one_piece);
					double percent = (double) (i + 1) * 100 / 2000;
					publishProgress(percent); // 更新百分比
				}

				mLoadEndTime = System.currentTimeMillis();
				return mLoadEndTime - mLoadStartTime;
			}

			@Override
			protected void onProgressUpdate(Double... values) {
				myTextView.setText("当前加载进度" + decf.format(values[0]) + "%");
			}

			@Override
			protected void onPostExecute(Long result) {
				myTextView.setText("读取2000张图片一共耗时" + result + "毫秒");
			}
		}.execute();
	}

	/**
	 * 读取图片
	 * 
	 * @param context
	 * @param resId
	 * @return Bitmap
	 */
	public Bitmap readBitmap(Context context, int resId) {
		BitmapFactory.Options opts = new BitmapFactory.Options();
		opts.inPreferredConfig = Config.RGB_565;
		opts.inPurgeable = true;
		opts.inInputShareable = true;
		InputStream is = context.getResources().openRawResource(resId);
		return BitmapFactory.decodeStream(is, null, opts);
	}
}

 

asynctask.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:layout_width="fill_parent" 
	android:layout_height="fill_parent"
	android:orientation="vertical">
	<Button android:layout_width="fill_parent"
		android:layout_height="wrap_content" 
		android:text="AsyncTask循环加载2000张图片"
		android:id="@+id/myButton" />
	<TextView android:layout_width="fill_parent"
		android:layout_height="wrap_content" 
		android:gravity="center"
		android:text="点击按钮开始加载图片" 
		android:id="@+id/myTextView" />
</LinearLayout>