Question

我有一个MainActivity，它包含两个片段（Frag1和Frag2）

我要做的是：每当我点击Frag1中的按钮时，“单击按钮”字符串应该显示在Frag2的EditText中。

我正在使用ViewPager，因此我没有片段ID 我设置了一个通信器界面和一个片段标签但我不知道我是否正确设置了碎片标记。

这是我的代码：

Communicator界面

public interface Communicator {
    public void respond(String data);

}

Frag1

public class Frag1 extends Fragment implements OnClickListener { 

Button button1;
Communicator comm;

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

    return inflater.inflate(R.layout.frag1, container, false);
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    comm = (Communicator)getActivity();

    button1 = (Button) getActivity().findViewById(R.id.button1);
    button1.setOnClickListener(this);
}

@Override
public void onClick(View view) {
    comm.respond("The button was clicked");     


}

}

MainActivity

public class MainActivity extends FragmentActivity implements Communicator {

ViewPager viewPager = null; 

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    viewPager = (ViewPager)findViewById(R.id.pager);    
    FragmentManager fragmentManager = getSupportFragmentManager();
    viewPager.setAdapter(new MyAdapter(fragmentManager));
    viewPager.setOffscreenPageLimit(2);
}

public class MyAdapter extends FragmentStatePagerAdapter {  

    public MyAdapter (FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int i) {
        Fragment fragment = null;

        if (i == 0)
        {
            fragment = new Frag1();
        }
        if (i == 1)
        {
            fragment = new Frag2();
        }
        return fragment;
    }

    @Override
    public int getCount() {
        return 2;
    }   
}

@Override
public void respond(String data) {

    Frag2 frag2 = new Frag2();
    getSupportFragmentManager().beginTransaction().add(frag2, "Hello").commit();

    Frag2 frag = (Frag2) getSupportFragmentManager().findFragmentByTag("Hello");
    frag.changeText(data);
}

}

Frag2

public class Frag2 extends Fragment { 

    EditText edittext1;

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

        return inflater.inflate(R.layout.frag2, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        edittext1 = (EditText) getActivity().findViewById(R.id.edit1);
    }

    public void changeText(String data) {
        edittext1.setText(data);
    }

}

单击Frag1

中的按钮后，LogCat中出现

错误

02-10 21:22:09.210: E/AndroidRuntime(9760): FATAL EXCEPTION: main
02-10 21:22:09.210: E/AndroidRuntime(9760): java.lang.NullPointerException
02-10 21:22:09.210: E/AndroidRuntime(9760):     at lmf.test5.MainActivity.respond(MainActivity.java:59)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at lmf.test5.Frag1.onClick(Frag1.java:35)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at android.view.View.performClick(View.java:4212)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at android.view.View$PerformClick.run(View.java:17476)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at android.os.Handler.handleCallback(Handler.java:800)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at android.os.Handler.dispatchMessage(Handler.java:100)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at android.os.Looper.loop(Looper.java:194)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at android.app.ActivityThread.main(ActivityThread.java:5371)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at java.lang.reflect.Method.invokeNative(Native Method)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at java.lang.reflect.Method.invoke(Method.java:525)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
02-10 21:22:09.210: E/AndroidRuntime(9760):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

我认为你应该等待在respond(String data)中执行挂起的交易。但你可以执行：

getSupportFragmentManager().executePendingTransactions();

之前：

Frag2 frag = (Frag2) getSupportFragmentManager().findFragmentByTag("Hello");
frag.changeText(data);

我认为它应该没问题

顺便说一句，您应该像在Google导游中使用Deliver a Message to a Fragment一样重写您的void respond(String data)。问题是，在添加新片段时，您应该使用setArguments传递数据，但是当片段已经存在时，您可以在其上调用方法。这样你就不需要executePendingTransactions（）。

碎片到碎片通信NPE

1 个答案: