android - 从 fragment 到 Activity 的通信数据不起作用

我已经有一段时间了，经过几次失败的尝试，我已经很接近实现自己的目标了。我已经从该站点挖掘出各种答案，最有帮助的是：

Passing data between a fragment and its container activity

我已经将Harlo的所有代码段都实现到了程序中，但是仍然有一个问题。

当我运行该应用程序时，我点击列表项以加载“ Core”片段，当崩溃时，我得到了可怕的“不幸的是应用程序已停止”。

我的片段代码在下面，并且我突出显示了有问题的行，还包括了logcat的相关部分。

任何帮助将不胜感激。

谢谢

加里

import android.app.Activity;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.os.Bundle;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.view.View.OnClickListener;


public class CoreFragment extends Fragment{

int index;
Button Button1,Button2,Button3;
String Str;
OnDataPass dataPasser;

@Override
public void onAttach(Activity a) {
    super.onAttach(a);
        dataPasser = (OnDataPass) a;
}


public static CoreFragment newInstance(int index) {
    CoreFragment coreFragment = new CoreFragment();
    coreFragment.index = index;
    return coreFragment;
}


public interface OnDataPass {
    public void onDataPass(String data);
}

public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    if (container == null) {
        // We have different layouts, and in one of them this
        // fragment's containing frame doesn't exist. The fragment
        // may still be created from its saved state, but there is
        // no reason to try to create its view hierarchy because it
        // won't be displayed. Note this is not needed -- we could
        // just run the code below, where we would create and return
        // the view hierarchy; it would just never be used.
        return null;
    }
    RelativeLayout mRelativeLayout = (RelativeLayout) inflater.inflate(R.layout.corefragment,
            container, false);

    Button Button1 = (Button) mRelativeLayout.findViewById(R.id.Button1);
    Button1.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
        Str = "I ";
        passData(Str);
            }

       public void passData(String data) {
            data = Str;
            dataPasser.onDataPass(data);
        }

    });
    return mRelativeLayout;
}
}//end

LogCat

01-18 12:19:18.430: W/dalvikvm(1601): threadid=1: thread exiting with uncaught exception (group=0x40acf228)
01-18 12:19:18.440: E/AndroidRuntime(1601): FATAL EXCEPTION: main
01-18 12:19:18.440: E/AndroidRuntime(1601): java.lang.ClassCastException: com.epsilonitsystems.fragger.MainActivity cannot be cast to com.epsilonitsystems.fragger.CoreFragment$OnDataPass
01-18 12:19:18.440: E/AndroidRuntime(1601):     at com.epsilonitsystems.fragger.CoreFragment.onAttach(CoreFragment.java:25)

嗨，TNR，
谢谢你，因为我对片段说的很新，它们证明确实很痛苦！我已经添加了您建议的行，现在我崩溃了！ LogCat在下面。谢谢您到目前为止的帮助，我很高兴能解决这个问题！！

01-23 15:30:40.659: W/dalvikvm(3098): threadid=1: thread exiting with uncaught exception (group=0x40acf228)
01-23 15:30:40.749: E/AndroidRuntime(3098): FATAL EXCEPTION: main
01-23 15:30:40.749: E/AndroidRuntime(3098): java.lang.NullPointerException
01-23 15:30:40.749: E/AndroidRuntime(3098):     at com.epsilonitsystems.fragger.MainActivity.onDataPass(MainActivity.java:33)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at com.epsilonitsystems.fragger.CoreFragment$1.passData(CoreFragment.java:69)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at com.epsilonitsystems.fragger.CoreFragment$1.onClick(CoreFragment.java:62)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at android.view.View.performClick(View.java:3549)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at android.view.View$PerformClick.run(View.java:14393)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at android.os.Handler.handleCallback(Handler.java:605)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at android.os.Looper.loop(Looper.java:154)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at android.app.ActivityThread.main(ActivityThread.java:4945)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at java.lang.reflect.Method.invokeNative(Native Method)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at java.lang.reflect.Method.invoke(Method.java:511)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
01-23 15:30:40.749: E/AndroidRuntime(3098):     at dalvik.system.NativeStart.main(Native Method)

再次感谢。

最佳答案

您正在尝试将接口的活动类型化。因此，您正在得到ClassCastException。检查您的MainActivity是否正在实现onDataPass接口。如果它实现了onDataPass接口，那么您的问题就可以解决。希望它能工作。

更新的答案：

如下更改您的onClick()。您已经编写了passData()，但从未调用过将数据传递给onDataPass()的方法，这将100％确定您的问题。

@Override
public void onClick(View v) {
 Str = "I ";
 passData(Str);
}