【发布时间】：2015-12-07 01:52:58
【问题描述】：
我已经搜索了很多关于如何使用SlidingTabLayout 在片段之间进行通信的内容，但还没有真正得到一个好的答案。 （尽管我仍然对 android 不熟悉）我认为我离解决方案不太远 - 任何帮助将不胜感激。目前正在制作一个计步器项目，我正在尝试在检测到步骤时更新SlidingTabLayout 中的TextView。我有一个 StepListener 接口，当检测到 Step 时会收到通知，我认为我的 Tabs 可以简单地实现该接口并收到通知，从而在我进行时增加我的 TextView 但没有成功。
我试过this。当 debuggin 注意到它到达 Tab1 中的 stepsChanged 方法但随后应用程序崩溃。任何帮助表示赞赏。
我的 MainActivity....
public class PedometerActivity extends ActionBarActivity implements StepListener, ServiceConnection {
// applying buissness rules
public static final int DAILY_GOAL = 10000;
public float currentSteps;
// Declaring Your View and Variables for the UI
Toolbar toolbar;
ViewPager pager;
ViewPagerAdapter adapter;
SlidingTabLayout tabs;
CharSequence Titles[] = {"Home", "MyStats"};
int Numboftabs = 2;
//declaring Variables for acess to Db and Prefs
UserLocalStore userLocalStore;
SharedPreferences sharedPreferences;
//declaring variables for the Step\Service
private StepService mStepService = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_pedometer);
userLocalStore = new UserLocalStore(this);
this.startStepService();
this.bindStepService();
/* sharedPreferences = getSharedPreferences("steps", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putInt("currentSteps", numSteps); TODO remove this
editor.commit();*/
// Creating The Toolbar and setting it as the Toolbar for the activity
toolbar = (Toolbar) findViewById(R.id.tool_bar);
setSupportActionBar(toolbar);
// Creating The ViewPagerAdapter and Passing Fragment Manager, Titles fot the Tabs and Number Of Tabs.
adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs);
// Assigning ViewPager View and setting the adapter
pager = (ViewPager) findViewById(R.id.pager);
pager.setAdapter(adapter);
// Assiging the Sliding Tab Layout View
tabs = (SlidingTabLayout) findViewById(R.id.tabs);
tabs.setDistributeEvenly(true); // To make the Tabs Fixed set this true, This makes the tabs Space Evenly in Available width
// Setting Custom Color for the Scroll bar indicator of the Tab View
tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
@Override
public int getIndicatorColor(int position) {
return getResources().getColor(R.color.tabsScrollColor);
}
});
// Setting the ViewPager For the SlidingTabsLayout
tabs.setViewPager(pager);
}
@Override
public void stepsChanged(float numSteps) {
//TODO /////
for (int loop = 0; loop < adapter.getCount(); loop++) {
if (adapter.getItem(0) instanceof StepListener) {
((StepListener) adapter.getItem(0)).stepsChanged(numSteps);
}//end of if
}// end of for loop
}
public float getCurrentSteps(float currentSteps) {
return currentSteps;
}
/**
* currently unused....code
*
* @return
*/
private boolean authenticate() {
return userLocalStore.getUserLoggedIn();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onPostResume() {
super.onPostResume();
}
private void startStepService() {
this.startService(new Intent(PedometerActivity.this, StepService.class));
}
/**
* binds Pedometer Activity to the Service class
* (I.e this service is going to communicate to this Activity)
* must implement the ServiceConnection interface here
*/
private void bindStepService() {
this.bindService(new Intent(PedometerActivity.this, StepService.class),
this, Context.BIND_AUTO_CREATE + Context.BIND_DEBUG_UNBIND);
}
@Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
mStepService = ((StepService.StepBinder) iBinder).getService();
mStepService.registerStepListener(this);
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
}
}
我的 Tab1....
public class Tab1 extends Fragment implements StepListener {
private static final int DAILY_GOAL = 10000;
UserLocalStore userLocalStore;
TextView tvStepValue;
//float currentSteps;
Database db;
private Activity activity;
private PieChart mPieChart;
private PieModel sliceGoal, sliceCurrent;
StepCounter mStepCounter;
public Tab1() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.tab_1, container, false);
tvStepValue = (TextView) v.findViewById(R.id.tvStepValue);
// mPieChart = (PieChart) v.findViewById(R.id.piechart);
// load data to PieCHart
return v;
}
/**
* method needed in Order to give the fragment a context to be used in conjunction with SharedPref/Database
*
* @param activity
*/
@Override
public void onAttach(Activity activity) {
this.activity = activity;
super.onAttach(activity);
}
private void loadData(View v) {
}
@Override
public void stepsChanged(float numSteps) {
tvStepValue.setText(String.valueOf(numSteps));
}
}
应用崩溃时我的错误消息....
09-10 17:21:29.748 26336-26336/com.example.calum.myslidingtablayout E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.calum.myslidingtablayout.Tab1.stepsChanged(Tab1.java:81)
at com.example.calum.myslidingtablayout.PedometerActivity.stepsChanged(PedometerActivity.java:100)
at com.example.calum.myslidingtablayout.StepCounter.onSensorChanged(StepCounter.java:50)
at android.hardware.SystemSensorManager$ListenerDelegate$1.handleMessage(SystemSensorManager.java:250)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4867)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
at dalvik.system.NativeStart.main(Native Method)
【问题讨论】：