Question

我想知道使用Handler.Callback。我在网上找不到任何详细信息。在以下资源中： http://files.dcarl.me/books/First_Collection_Programming_Books/Asynchronous%20Android%20%5BeBook%5D.pdf 据说：

我们可以通过传递一个实例来优先考虑组合而不是继承处理程序构造期间的Handler.Callback。

资源上的示例如下：

public static class SpeakHandler extends Handler {
    public static final int SAY_HELLO = 0;
    public static final int SAY_BYE = 1;
    public SpeakHandler(Callback callback) {
        super(callback);
    }
    @Override
    public void handleMessage(Message msg) {
        switch(msg.what) {
            case SAY_HELLO:
                sayWord("hello"); break;
            case SAY_BYE:
                sayWord("goodbye"); break;
            default:
                super.handleMessage(msg);
        }
    }
    private void sayWord(String word) { … }
}
public static class Speaker implements Handler.Callback {
    public static final int SAY_WORD = 2;
    @Override
    public boolean handleMessage(Message msg) {
        if (msg.what == SAY_WORD) {
            sayWord((String)msg.obj);
            return true;
        }
        return false;
    }
    private void sayWord(String word) { … }
}
Handler h = new SpeakHandler(new Speaker());
h.sendMessage(Message.obtain(handler, Speaker.SAY_WORD, "!?"));

为什么我需要上面代码中的Handler.Callback？我可以做同样的事情：

    public static class SpeakHandler extends Handler {
    public static final int SAY_HELLO = 0;
    public static final int SAY_BYE = 1;
    public static final int SAY_WORD = 2;
    @Override
    public void handleMessage(Message msg) {
        switch(msg.what) {
            case SAY_HELLO:
                sayWord("hello"); break;
            case SAY_BYE:
                sayWord("goodbye"); break;
            case SAY_WORD:
                sayWord((String)msg.obj); break;
            default:
                super.handleMessage(msg);
        }
    }
    private void sayWord(String word) { … }
}

什么是Handler.Callback？在官方文件中，据说

您可以在实例化Handler时使用回调接口来避免必须实现自己的Handler子类。我不明白这意味着什么......

Handler.Callback - 在从Handler实例化时更喜欢组合而不是继承

0 个答案: