我试图处理图书馆Otto并尝试an example here
我能够运行这个例子。但是我想使用组件，对于这些组件我是一个稍微改变的例子并且得到了错误
MainActivity：
public class MainActivity extends ActionBarActivity {
public static Bus bus;
private TextView mainTxt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mainTxt = (TextView) findViewById(R.id.mainText);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
bus = new Bus(ThreadEnforcer.MAIN);
bus.register(this);
}
@Subscribe
public void getMessage(String s) {
Toast.makeText(this, s, Toast.LENGTH_LONG).show();
mainTxt.setText(s);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
TestData t = new TestData();
t.message="Hello from the activity";
bus.post(t);
return true;
}
return super.onOptionsItemSelected(item);
}
public class TestData {
public String message;
}
}
片段：
public class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
View button = rootView.findViewById(R.id.fragmentbutton);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
MainActivity.bus.post("Hello from the Fragment");
}
});
MainActivity.bus.register(this);
return rootView;
}
@Subscribe
public void getMessage(MainActivity.TestData data) {
Toast.makeText(getActivity(), data.message, Toast.LENGTH_LONG).show();
}
@Produce
public String produceEvent() {
return "Starting up";
}
}
我刚改变了：
@Subscribe
public void getMessage(String s) {
Toast.makeText(this, s, Toast.LENGTH_LONG).show();
mainTxt.setText(s);
}
或者更确切地说是添加了mainTxt.setText(s);我希望对事件进行分段，不仅会显示消息并在mainTxt中设置值
错误：
01-09 21:11:22.448 28849-28849/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{gcm.colibri.com.ottotest/gcm.colibri.com.ottotest.MainActivity}: java.lang.RuntimeException: Could not dispatch event: class java.lang.String to handler [EventHandler public void gcm.colibri.com.ottotest.MainActivity.getMessage(java.lang.String)]: null
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4464)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:822)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:589)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.RuntimeException: Could not dispatch event: class java.lang.String to handler [EventHandler public void gcm.colibri.com.ottotest.MainActivity.getMessage(java.lang.String)]: null
at com.squareup.otto.Bus.throwRuntimeException(Bus.java:456)
at com.squareup.otto.Bus.dispatch(Bus.java:386)
at com.squareup.otto.Bus.dispatchProducerResultToHandler(Bus.java:252)
at com.squareup.otto.Bus.register(Bus.java:205)
at gcm.colibri.com.ottotest.PlaceholderFragment.onCreateView(PlaceholderFragment.java:33)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:548)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1133)
at android.app.Activity.performStart(Activity.java:4529)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1929)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4464)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:822)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:589)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at gcm.colibri.com.ottotest.MainActivity.getMessage(MainActivity.java:34)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.squareup.otto.EventHandler.handleEvent(EventHandler.java:89)
at com.squareup.otto.Bus.dispatch(Bus.java:384)
at com.squareup.otto.Bus.dispatchProducerResultToHandler(Bus.java:252)
at com.squareup.otto.Bus.register(Bus.java:205)
at gcm.colibri.com.ottotest.PlaceholderFragment.onCreateView(PlaceholderFragment.java:33)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
帮助我理解
答案 0 :(得分：0)
mainTxt字段似乎为null。确保它不是null。例如，在if (mainTxt != null)中添加getMessage(String)之类的支票。