正在处理片段内点击按钮时向我的MainActivity发送一些字符串数据。它似乎不是一个困难的程序，但我在某个地方被捆绑并收到NullPointerException。我假设它与我使用界面的方式有关。 Android新手，建议和评论将不胜感激。谢谢！
接口代码：
public interface BtnInterface {
public void btnClicked(String x, String y, String z, String w);
}
主要活动单位：
public class MainActivity extends Activity implements BtnInterface{
Fragment_X frag;
FragmentTransaction ft;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
frag = new Fragment_X();
frag.setInterface(this);
ft = getFragmentManager().beginTransaction();
ft.add(R.id._frag_container, frag);
ft.commit();
}
@Override
public void btnClicked(String x, String y,String z, String w) {
Log.d("data-check", x);
}
FRAGMENT SNIPPET：
public class Fragment_X extends Fragment {
View v;
Button btn;
BtnInterface buttonInterface;
String x, y, z, w;
String choices1 = {"random", "values"}
String choices2 = {"random", "values"}
String choices3 = {"random", "values"}
String choices4 = {"random", "values"}
public void setInterface(BtnInterface buttonInterface) {
this.buttonInterface = buttonInterface;
}
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
v = inflater.inflate(R.layout.frag_layout, container,
false);
spin1 = (Spinner) v.findViewById(R.id.spin1);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),
R.layout.spinner_layout, choices1);
adapter.setDropDownViewResource(R.layout.spinner_dropdown);
spinSomewhere.setAdapter(adapter);
spin2 = (Spinner) v.findViewById(R.id.spin2);
ArrayAdapter<String> adapter1 = new ArrayAdapter<String>(getActivity(),
R.layout.spinner_layout, choices2);
adapter1.setDropDownViewResource(R.layout.spinner_dropdown);
spinFor.setAdapter(adapter1);
spin3 = (Spinner) v.findViewById(R.id.spin3);
ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(getActivity(),
R.layout.spinner_layout, choices4);
adapter2.setDropDownViewResource(R.layout.spinner_dropdown);
spinXp.setAdapter(adapter2);
spin4 = (Spinner) v.findViewById(R.id.spin4);
ArrayAdapter<String> adapter3 = new ArrayAdapter<String>(getActivity(),
R.layout.spinner_layout, choices4);
adapter3.setDropDownViewResource(R.layout.spinner_dropdown);
spinWith.setAdapter(adapter3);
btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
x = spin1.getSelectedItem().toString();
y = spin2.getSelectedItem().toString();
z = spin3.getSelectedItem().toString();
w = spin4.getSelectedItem().toString();
buttonInterface.btnClicked(x,y,z,w);
}
});
return v;
}
}
错误日志：
05-30 21:27:35.230: E/AndroidRuntime(3016): FATAL EXCEPTION: main
05-30 21:27:35.230: E/AndroidRuntime(3016): Process: com.ex.app, PID: 3016
05-30 21:27:35.230: E/AndroidRuntime(3016): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ex.app/com.ex.app.MainActivity}: java.lang.NullPointerException
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.os.Handler.dispatchMessage(Handler.java:102)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.os.Looper.loop(Looper.java:136)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.ActivityThread.main(ActivityThread.java:5017)
05-30 21:27:35.230: E/AndroidRuntime(3016): at java.lang.reflect.Method.invokeNative(Native Method)
05-30 21:27:35.230: E/AndroidRuntime(3016): at java.lang.reflect.Method.invoke(Method.java:515)
05-30 21:27:35.230: E/AndroidRuntime(3016): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-30 21:27:35.230: E/AndroidRuntime(3016): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-30 21:27:35.230: E/AndroidRuntime(3016): at dalvik.system.NativeStart.main(Native Method)
05-30 21:27:35.230: E/AndroidRuntime(3016): Caused by: java.lang.NullPointerException
05-30 21:27:35.230: E/AndroidRuntime(3016): at com.ex.app.Fragment_X.onCreateView(Fragment_X.java:75)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.Fragment.performCreateView(Fragment.java:1700)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:890)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.BackStackRecord.run(BackStackRecord.java:684)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.Activity.performStart(Activity.java:5240)
05-30 21:27:35.230: E/AndroidRuntime(3016): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2168)
05-30 21:27:35.230: E/AndroidRuntime(3016): ... 11 more
答案 0 :(得分：1)
它为null，因为您在实例化后忘记将BtnInterface设置为Fragment_X。
<强>溶液
frag = new Fragment_X();
frag.setInterface(this);
ft = getFragmentManager().beginTransaction();
ft.add(R.id._frag_container, frag);
ft.commit();
答案 1 :(得分：0)
简单的回答。忘了最简单的一行：
btn = (Button) v.findViewById(R.id.btn);
正如我所说的......对Android来说很新。