Android一次性退出多个Activity的方法

package com.exit;
import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
public class ActivityManager
{
  private Context context;
  private static ActivityManager activityManager;
  public static ActivityManager getActivityManager(Context context)
  {
    if(activityManager == null)
    {
      activityManager = new ActivityManager(context);
    }
    return activityManager;
  }
  private ActivityManager(Context context)
  {
    this.context = context;
  }
  /**
   * task map，用于记录activity栈，方便退出程序（这里为了不影响系统回收activity，所以用软引用）
   */
  private final HashMap<String, SoftReference<Activity>> taskMap = new HashMap<String, SoftReference<Activity>>();
  /**
   * 往应用task map加入activity
   */
  public final void putActivity(Activity atv)
  {
    taskMap.put(atv.toString(), new SoftReference<Activity>(atv));
  }
  /**
   * 往应用task map加入activity
   */
  public final void removeActivity(Activity atv) {
    taskMap.remove(atv.toString());
  }
  /**
   * 清除应用的task栈，如果程序正常运行这会导致应用退回到桌面
   */
  public final void exit()
   {
    for (Iterator<Entry<String, SoftReference<Activity>>> iterator = taskMap.entrySet().iterator(); iterator.hasNext();)   {
      SoftReference<Activity> activityReference = iterator.next().getValue();
      Activity activity = activityReference.get();
      if (activity != null)
      {
        activity.finish();
      }
    }
    taskMap.clear();
  }
}

package com.exit;
import android.app.Activity;
import android.os.Bundle;
public class BaseActivity extends Activity {
  private ActivityManager manager = ActivityManager.getActivityManager(this);
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    manager.putActivity(this);
  }
  @Override
  protected void onDestroy() {
    super.onDestroy();
    manager.removeActivity(this);
  }
  public void exit(){
    manager.exit();
  }
}

package com.exit.activitys;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import com.exit.BaseActivity;
import com.exit.R;
public class ExitActivity extends BaseActivity implements OnClickListener{
  private Button start;
  private Button exit;
  private TextView tipTV;
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  start = (Button)findViewById(R.id.start_new_activity);
  exit = (Button)findViewById(R.id.exit_all_activity);
  tipTV = (TextView)findViewById(R.id.tip_tv);
  tipTV.setText("activity:"+this.toString());
  start.setOnClickListener(this);
  exit.setOnClickListener(this);
 }
  @Override
  public void onClick(View v) {
    if(v == start){
      Intent intent = new Intent(this , ExitActivity.class);
      startActivity(intent);
    }else if(v == exit){
      exit();
    }
  }
}