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【慕课网】AsyncTask的使用


package com.example.liuan.asynctask;

import android.os.AsyncTask;
import android.util.Log;


public class MyAsyncTask extends AsyncTask<Void,Void,Void>{

private static final String TAG="MyAsyncTask";
//doInBackGround:必须重写 异步执行后台线程将要完成的任务
//onPreExecute:执行后台耗时操作前被调用,通常用户完成一些初始化操作
//onPostExecute 当doInBackGround()完成后 系统会自动调用onPostExecute()方法,并将doInBackground 方法返回的值传给该方法
//onProgressUpdata:在doInBackGround()方法中调用publishProgress()方法更新任务的执行进度后,就会触发该方法
// 注意事项 必须在Ui线程 中创建和调用
// 2 是调用的 不要调用多次 否则抛出运行时异常
// 3 doInBackGround 是运行在主线程 其他运行在ui线程
// 4 四个方法都是习哦他能够调用的 不应该手动调用

// https://www.imooc.com//static/img/index/logo.png
@Override
protected Void doInBackground(Void... voids) {
Log.e(TAG, "doInBackground: ");
publishProgress();
return null;
}

@Override
protected void onPreExecute() {
Log.e(TAG, "onPreExecute: ");
}

@Override
protected void onPostExecute(Void aVoid) {
Log.e(TAG, "onPostExecute: " );

}

@Override
protected void onProgressUpdate(Void... values) {
Log.e(TAG, "onProgressUpdate: " );
}
}

//通过async更新图片

package com.example.liuan.asynctask;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLConnection;
import java.net.URL;

public class ImageTestActivity extends AppCompatActivity {

private static String URL = "https://www.imooc.com//static/img/index/logo.png";
private ImageView mIv;
private ProgressBar mPb;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_image_test);
initView();
initData();
}

private void initData() {
new MyAsyncTask().execute(URL);

}

private void initView() {
mIv = (ImageView) findViewById(R.id.iv);
mPb = (ProgressBar) findViewById(R.id.pb);
}

// 三个参数分别对应传入 参数类型 返回类型 和结果类型
class MyAsyncTask extends AsyncTask<String, Void, Bitmap> {
@Override
protected void onPreExecute() {
mPb.setVisibility(View.VISIBLE);

}

@Override
protected void onPostExecute(Bitmap bitmap) {
mPb.setVisibility(View.GONE);
mIv.setImageBitmap(bitmap);
}

@Override
protected Bitmap doInBackground(String... strings) {
// 获取传递进来的参数
String url = strings[0];
Bitmap bitmap = null;
URLConnection urlConnection;
InputStream is;
try {
urlConnection = new URL(url).openConnection();
// 获取输入流
is = urlConnection.getInputStream();
BufferedInputStream bis = new BufferedInputStream(is);
Thread.sleep(3000);
//通过decodeStream方法 解析输入流
bitmap = BitmapFactory.decodeStream(bis);
is.close();
bis.close();
} catch (IOException e) {


} catch (InterruptedException e) {

}
//将bitmap作为返回值
return bitmap;
}


}
}

//通过sayncTask更新进度条

package com.example.liuan.asynctask;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ProgressBar;

/**
* Created by liuan on 2018/3/18.
*/

public class ProgerssBarTestActivity extends AppCompatActivity {
private ProgressBar mPb;
private AsyncTask<Void, Integer, Void> mTask;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// TODO:OnCreate Method has been created, run FindViewById again to generate code
setContentView(R.layout.progressbar);
initView();
mTask = new MyAsyncTask().execute();
}

public void initView() {
mPb = (ProgressBar) findViewById(R.id.pb);
}


class MyAsyncTask extends AsyncTask<Void,Integer,Void>{

@Override
protected Void doInBackground(Void... voids) {
for (int i = 0; i < 100; i++) {
if(isCancelled()){
break;
}
publishProgress(i);
try {
Thread.sleep(300);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return null;

}

@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
if(isCancelled()){
return;
}
mPb.setProgress(values[0]);
}

@Override
protected void onCancelled() {
super.onCancelled();
}

@Override
protected void onCancelled(Void aVoid) {
super.onCancelled(aVoid);
}
}

@Override
protected void onDestroy() {
super.onDestroy();
if (mTask != null&&mTask.getStatus()==AsyncTask.Status.RUNNING) {
// 只是将对应asyncTask标记了为cancel状态 并不是真正的取消线程的执行。
//而且java无法粗暴的停止线程
mTask.cancel(true);

}

}

@Override
protected void onPause() {
super.onPause();

}
}




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