从(列表)适配器回调到活动 [英] Callback from (List)Adapter to Activity

问题描述

我有一个带有ListView的Actvivity，我设置了一个适配器

I have an Actvivity with a ListView, I set an adapter

MyAdapter extends BaseAdapter

该适配器具有回调接口

OnPdfClickedListener callback; 

public interface OnPdfClickedListener {
    public void onPdfClicked();

}

和活动"中

MyActvivity implements MyAdapter.OnPdfClickedListener

和

@Override
    public void onPdfClicked() {

    Log.d("TEST", "PDF CLICKED in ACTVIIVTY");

}

这与此处所述相同，喜欢碎片的魅力.从适配器尝试相同操作时，回调对象为null.

This is pretty much the same as described here, which works like charm for fragments. When trying the same from the adapter the callback object is null.

我也尝试实例化

OnPdfClickedListener callback = new OnPdfClickedListener() {

    @Override
    public void onPdfClicked() {
        // TODO Auto-generated method stub

    }
};

那时我没有错误，但是从未调用Activity中的相应方法.

I have no errors then but the respective method in the Activity is never called.

我的问题是1.为什么在片段中使用回调对象时，它为什么不为空，却从未实例化

My question is 1. why isn't the callback object null when used in a fragment, it's never instantiated

和2.如何从适配器回调到活动?

and 2. how can I callback to an Activity from an adapter?

推荐答案

1. 为什么在片段中使用回调对象时，它不为null，所以永远不会实例化

您创建的 callback 变量很可能未将您的 Activity 注册为侦听器(与 Activity ) OnPdfClickedListener 的实例，并且(可能)在事件发生时使用了该实例.

Your Activity most likely isn't registered as a listener, with the callback variable you created(which has nothing to do with the Activity) an instance of OnPdfClickedListener and (probably) used that when the event happened.

如何从适配器回调到活动?

how can I callback to an Activity from an adapter?

将对 Activity 的引用传递到您的 MyAdapter 类，将其强制转换为 OnPdfClickedListener ，然后使用该调用来调用 onPdfClicked 而不是当前的 callback 变量.

Pass a reference to the Activity to your MyAdapter class, cast it to OnPdfClickedListener and use that to call onPdfClicked instead of the current callback variable.

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