Question

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

Answer 1

通话时

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。

使用库Otto时出错

1 个答案: