image.png
AsynTask 异步任务
Android机制，不允许子线程更新UI界面，耗时操作需要开辟新的Thread执行；
Android为解决新线程不能更新UI组件问题，提供如下解决方案：
Handler线程之间通讯；
-
子线程中再次调用主线程；
runOnUiThread(new Runnable() { @Override public void run() { } }); AsynTask 异步任务
AsynTask 异步任务分析
代码运行示意效果图：
02.png-25kB
代码分析
01 初始化代码OnCreate：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
image = (ImageView) findViewById(R.id.imageView);
show = (TextView) findViewById(R.id.textView);
Button asynTask = (Button) findViewById(R.id.btn_Asyn);
asynTask.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
DownTask task = new DownTask();
try {
task.execute(new URL("http://img2.imgtn.bdimg.com/it/u=1698945203,1066999821&fm=11&gp=0.jpg"));
} catch (MalformedURLException e) {
e.printStackTrace();
}
}
});
}
02 AsyncTASK 异步任务实现代码
private class DownTask extends AsyncTask<URL, Integer, Bitmap> {
ProgressDialog progressDialog;
Bitmap bitmap;
int curDownSize;
@Override
//Asyn异步任务后台执行前初始化操作
protected void onPreExecute() {
Log.d(TAG, "onPreExecute01: ");
super.onPreExecute();
progressDialog = new ProgressDialog(MainActivity.this);
Log.d(TAG, "onPreExecute: 01");
//设置对话框标题
progressDialog.setTitle("下载任务对话框");
Log.d(TAG, "onPreExecute: 02");
//设置对话框内容
progressDialog.setMessage("下载任务正在执行中...");
Log.d(TAG, "onPreExecute: 03");
//设置对话框按钮取消
progressDialog.setCancelable(false);
Log.d(TAG, "onPreExecute: 04");
//设置对话框进度条最大值
progressDialog.setMax(100);
Log.d(TAG, "onPreExecute: 05");
//设置对话框进度条风格
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
Log.d(TAG, "onPreExecute: 06");
//设置对话框的进度条是否显示进度
progressDialog.setIndeterminate(false);
Log.d(TAG, "onPreExecute: 07");
progressDialog.show();
Log.d(TAG, "onPreExecute: 08");
KLog.d();
}
@Override
//Asyn异步任务后台开辟新线程执行任务，不能更新UI界面，需通过publishProgress（）
//函数将更新界面的值传递给onProgressUpdate函数
protected Bitmap doInBackground(URL... params) {
Log.d(TAG, "doInBackground02: ");
URL url = params[0];
int total = 0;
URLConnection connection = null;
BufferedInputStream bufferedInputStream = null;
try {
//上报链接请求
connection = params[0].openConnection();
//字节输入流
InputStream inputStream = connection.getInputStream();
//字节缓冲输入流
bufferedInputStream = new BufferedInputStream(inputStream);
//计算文件的总大小
total = connection.getContentLength();
Log.d(TAG, "doInBackground: total =" + total);
byte[] bytes = new byte[1024];
int hasRead = 0;
//数组cache输出流
ByteArrayOutputStream bos = new ByteArrayOutputStream();
Log.d(TAG, "doInBackground:inputStream.read(bytes)= ");
while ((hasRead = bufferedInputStream.read(bytes)) != -1) {
//curDownSize 实时读取文件大小
curDownSize += hasRead;
Log.d(TAG, "doInBackground: curDownSize=" + curDownSize);
//发送文件下载的百分比
publishProgress((int) curDownSize * 100 / total);
Log.d(TAG, "doInBackground: " + (int) curDownSize * 100 / total);
//读取一个缓冲流，就实时写入一个缓冲流
bos.write(bytes, 0, hasRead);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//数据流转换为bitmap ByteArrayOutputStream.toByteArray（）方法
bitmap = BitmapFactory.decodeByteArray(bos.toByteArray(), 0, bos.toByteArray().length);
//关闭打开的数据流，先打开的后关闭，后打开的先关闭
fis.close();
bos.close();
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
@Override
//接收doInBackground传递过来的数据，实时更新UI
protected void onProgressUpdate(Integer... values) {
Log.d(TAG, "onProgressUpdate03: ");
super.onProgressUpdate(values);
progressDialog.setProgress(values[0]);
show.setText(String.valueOf(values[0]));
}
@Override
//最后执行的函数
protected void onPostExecute(Bitmap bitmap) {
Log.d(TAG, "onPostExecute04: ");
super.onPostExecute(bitmap);
progressDialog.dismiss();
image.setImageBitmap(bitmap);
}
}
