Android 线程异步之：AsyncTask

﹏ヽ暗。殇╰゛Y 2023-06-18 09:54 25阅读 0赞

package littest.ghq.com.test;
    
    import android.app.DownloadManager;
    import android.app.ProgressDialog;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.media.Image;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.os.Message;
    import android.support.v7.app.AppCompatActivity;
    import android.util.Log;
    import android.view.View;
    import android.view.textclassifier.ConversationActions;
    import android.widget.Button;
    import android.widget.ImageView;
    
    import java.io.ByteArrayOutputStream;
    import java.io.InputStream;
    import java.net.URLConnection;
    import java.util.logging.Handler;
    import java.util.logging.LogRecord;
    
    
    public class MainActivity extends AppCompatActivity {
    
        //param s是异步任务所需的参数类型，也是doInbackground(params)方法的参数类型。（异步任务的输入参数例如URL）
        //progress是进度的参数类型，也就是onpostExecute的参数（例进度条）
        //Result是任务返回的参数类型
        //AsyncTask的实例只能在UI线程中创建启动（调用execute方法），不能手写的几个方法一定要记住
    
        private static final String sImageUrl = "http://localhost:8080/res/mipmap-hdpi/ic_launcher.png";
        private Button mLoadButton;
        private ProgressDialog mprogress;
        private ImageView mImage;
        protected void onCreate(Bundle savedInstanceState){
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            Log.d("异步下载图片",">>onCreate");
            mprogress = new ProgressDialog(this);
    
            mImage =(ImageView)this.findViewById(R.id.image);
            mLoadButton = (Button)this.findViewById(R.id.Load);
            mLoadButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    new DownloadImageTask().execute(sImageUrl);
                }
            });
    
    
        }
        private class DownloadImageTask extends AsyncTask<String ,Integer,Bitmap>{
    
            @Override
            protected void onPreExecute(){
                super.onPreExecute();
                mprogress.setMessage("图片正在下载，请稍后");
                mprogress.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                mprogress.setMax(100);
                mprogress.setProgress(0);
                mprogress.show();
            }//展示出进度条
    
            @Override
            protected Bitmap doInBackground(String... urls) {
                Bitmap bitmap= null;
                URLConnection connection;
                InputStream is;
                ByteArrayOutputStream bos;
                int len;
                float count=0,total=100;
                try{
                    connection =(URLConnection)new java.net.URL(urls[0]).openConnection();
                    total = (int)connection.getContentLength();
                    is = connection.getInputStream();
                    bos=new ByteArrayOutputStream();
                    byte[] data = new byte[1024];
                    while((len=is.read(data))!=-1){
                        count+=len;
                        bos.write(data,0,len);
                        publishProgress((int)(count/total*100));
                    }
                    bitmap = BitmapFactory.decodeByteArray(bos.toByteArray(),0,bos.toByteArray().length);
                    is.close();
                    bos.close();
    
                }catch (Exception e){
                    e.printStackTrace();
                }
                return bitmap;
            }
    
            @Override
            protected  void onProgressUpdate(Integer...values){
                super.onProgressUpdate();
                mprogress.setProgress(values[0]);
            }
    
            @Override
            protected void onPostExecute(Bitmap result){
                if(result!=null){
                    mprogress.setProgress(100);
                    mprogress.setMessage("图片下载完成");
                    mprogress.dismiss();
                    mImage.setImageBitmap(result);
                }else{
                    mprogress.setMessage("图片下载失败");
                }
            }
        }
    }