引子

• 随着项目的发展，activity的代码变得越来越庞杂，不易维护。这便出现了诸如MVP等模式来分层实现以达到给activity减负的效果，从而降低业务逻辑的耦合，提高可维护性。本文从另外一个角度出发，利用命令模式来实现给activity瘦身的目标。采用本文的方案，同样可以将业务逻辑抽离，并于后台执行，同时提供了不错的取消机制。

接口

• iCmd接口，主要api是exe方法，返回值是bundle对象；其他mTag，mCanceled用于取消相关

public abstract class iCmd {
    private boolean mCanceled = false;
    private Object mTag;

    public void cancel() {
        mCanceled = true;
    }

    public boolean isCanceled() {
        return mCanceled;
    }

    public Object getTag() {
        return mTag;
    }

    public iCmd setTag(Object tag) {
        mTag = tag;
        return this;
    }

    public abstract Bundle exe() throws Exception;
}

• iCmdListener 命令监听接口，onPreExecute负责命令开始的通知；onPostExecute负责命令结束的通知并带回返回结果

public interface iCmdListener {
    public void onPreExecute();

//  public void onProgressUpdate(int progress);

    public void onPostExecute(Bundle resultBundle);

}

• iCmdExecutor命令执行器，下列代码仅列出主要api，具体的实现文后的github地址

public class iCmdExecutor {
//用于取消和具体tag相关的cmd
    public static void cancelAll(final Object tag)

//异步执行该命令，并在主线程执行回调通知
    public static void exeAsync(final iCmd cmd, final iCmdListener listener,
            Object tag)

//同步执行该命令，并在当前线程执行回调通知
    public static void exeSync(iCmd cmd, iCmdListener listener, Object tag)

}

用法

• 实现具体cmd

public class CmdAdd extends iCmd {
    private static final String TAG = "test";
    private BigInteger a;
    private BigInteger b;

    public CmdAdd(BigInteger a, BigInteger b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public Bundle exe() throws InterruptedException {
        Log.i(TAG, this + ", exe, tid=" + Thread.currentThread().getId());
        Thread.sleep(5000);// demo for long operation
        Bundle bundle = new Bundle();
        bundle.putString("result", a.add(b).toString());
        return bundle;
    }

}

• 调用该命令

iCmdExecutor.exeAsync(new CmdAdd(new BigInteger("123"), new BigInteger(
                "12345678901234567890123456789012345678901234567890")),
                new iCmdListener() {

                    @Override
                    public void onPreExecute() {
                        Log.e(TAG, "onPreExecute, tid="
                                + Thread.currentThread().getId());
                    }

                    @Override
                    public void onPostExecute(Bundle resultBundle) {
                        Log.e(TAG, "onPostExecute, tid="
                                + Thread.currentThread().getId()
                                + ", resultBundle=" + resultBundle);
                        if (null != resultBundle) {
                            String res = resultBundle.getString("result");
                            tvAddResult.setText(res);
                        }
                    }
                }, this);

• 在activity退出时取消

iCmdExecutor.cancelAll(this);

链接

• https://github.com/cheyiliu/AsyncCmdForAndroid