安卓中實作異步任務（2）——使用AsyncTask實作

問題背景

實作demo

（1）實作我們的AsyncTask子類

import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MyAsyncTask extends AsyncTask<Integer,Integer,Integer> {
    private final String TAG = "AsyncTask";
    private TextView textView;
    private ProgressBar progressBar;
    private Context context;
    public MyAsyncTask(TextView textView, ProgressBar progressBar, Context context) {
        this.textView = textView;
        this.progressBar = progressBar;
        this.context = context;
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        Log.d(TAG,"onPreExecute(): " + Thread.currentThread().getName());
    }
    @Override
    protected Integer doInBackground(Integer... ints) {
        Integer count = ints[0];
        while (count < 10 && !isCancelled()){
            // isCancelled()表示判斷目前任務是否被取消，防止在取消異步任務的時候循環不能及時停下
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            count++;
            Log.d(TAG,"doInBackground(): "+ Thread.currentThread().getName() +" "+count);
            publishProgress(count);
        }
        return count;
    }
    @Override
    protected void onPostExecute(Integer i) {
        Log.d(TAG,"onPostExecute(): "+ Thread.currentThread().getName());
        textView.setText(i + "");
    }
    @Override
    protected void onProgressUpdate(Integer... values) {
        Log.d(TAG,"onProgressUpdate(): " + Thread.currentThread().getName());
        textView.setText(values[0]+"");
        progressBar.setProgress(values[0]);
    }
    @Override
    protected void onCancelled() {
        Log.d(TAG,"nCancelled(): "+Thread.currentThread().getName());
        super.onCancelled();
        Toast.makeText(context,"任務取消成功", Toast.LENGTH_LONG).show();
    }
}

           

（2）建立我們的activity，對應layout布局如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".thread.AsyncTaskActivity">
    <TextView
        android:id="@+id/textView"
        android:hint="0"
        android:layout_gravity="center_horizontal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <ProgressBar
        style="@android:style/Widget.ProgressBar.Horizontal"
        android:id="@+id/progressBar"
        android:progress="0"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <Button
            android:text="啟動任務"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:onClick="doTaskClick" />
        <Button
            android:text="取消任務"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentEnd="true"
            android:onClick="cancelTaskClick" />
    </RelativeLayout>

</LinearLayout>
           

（3）對應我們activity的代碼如下：

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;

public class AsyncTaskActivity extends AppCompatActivity {
    private TextView textView;
    private ProgressBar progressBar;
    private MyAsyncTask myAsyncTask;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_async_task);
        textView= findViewById(R.id.textView);
        progressBar= findViewById(R.id.progressBar);
    }

    public void doTaskClick(View view){
        myAsyncTask = new MyAsyncTask(textView, progressBar,this);
        // 執行異步任務，傳入初始參數
        myAsyncTask.execute(1);
    }

    public void cancelTaskClick(View view){
        // 取消異步任務
        myAsyncTask.cancel(true);
    }
}
           

執行結果如下：

關鍵代碼分析