Android入門之在子執行緒中呼叫Handler詳解

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <EditText
        android:id="@+id/inputNum"
        android:inputType="number"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="請輸入計算範圍"/>
    <Button
        android:id="@+id/buttonCalc"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="開始計算"/>
</LinearLayout>

package org.mk.android.demo;
 
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
 
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
 
import java.util.ArrayList;
import java.util.List;
 
public class MainActivity extends AppCompatActivity {
 
    private static final String INPUT_NUM = "inputNum";
    private EditText inputNum;
    private Button buttonCal;
    CalThread calThread;
 
    class CalThread extends Thread
    {
        public Handler mHandler;
 
        public void run()
        {
            Looper.prepare();
            mHandler = new Handler(new Handler.Callback() {
                @Override
                public boolean handleMessage(@NonNull Message msg) {
                    if(msg.what == 101)
                    {
                        int inputNum = msg.getData().getInt(INPUT_NUM);
                        List<Integer> nums = new ArrayList<Integer>();
                        // 計算從2開始、到upper的所有質數
                        outer:
                        for (int i = 2 ; i <= inputNum ; i++)
                        {
                            // 用i處於從2開始、到i的平方根的所有數
                            for (int j = 2 ; j <= Math.sqrt(i) ; j++)
                            {
                                // 如果可以整除，表明這個數不是質數
                                if(i != 2 && i % j == 0)
                                {
                                    continue outer;
                                }
                            }
                            nums.add(i);
                        }
                        // 使用Toast顯示統計出來的所有質數
                        Toast.makeText(MainActivity.this , nums.toString()
                                , Toast.LENGTH_LONG).show();
                    }
                    return false;
                }
            });
 
            Looper.loop();
        }
    }
    public void cal(View source)
    {
        // 建立訊息
        Message msg = new Message();
        msg.what = 101;
        Bundle bundle = new Bundle();
        bundle.putInt(INPUT_NUM ,
                Integer.parseInt(inputNum.getText().toString()));
        msg.setData(bundle);
        // 向新執行緒中的Handler傳送訊息
        calThread.mHandler.sendMessage(msg);
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        buttonCal=(Button)findViewById(R.id.buttonCalc);
        inputNum=(EditText)findViewById(R.id.inputNum);
        buttonCal.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                cal(view);
            }
        });
        calThread=new CalThread();
        calThread.start();
    }
}