活动 主要活动前两颗星

我找不到这个问题的任何解决方案。
这里是。

我有两个活动：主活动和三角形活动，我想在应用程序启动时看到主活动。

这是我的主要活动：

public class MainActivity extends Activity {
    // declare properties
    private String[] mNavigationDrawerItemTitles;
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;

    private ActionBarDrawerToggle mDrawerToggle;

    // nav drawer title
    private CharSequence mDrawerTitle;

    // used to store app title
    private CharSequence mTitle;

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

        // for proper titles
        mTitle = mDrawerTitle = getTitle();

        // initialize properties
        mNavigationDrawerItemTitles = getResources().
                getStringArray(R.array.navigation_drawer_items_array);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

        // list the drawer items
        ObjectDrawerItem[] drawerItem = new ObjectDrawerItem[4];

        drawerItem[0] = new ObjectDrawerItem(R.drawable.triangle, "Trougao");
        drawerItem[1] = new ObjectDrawerItem(R.drawable.rec, "Cetvorougao");
        drawerItem[2] = new ObjectDrawerItem(R.drawable.hexagon, "Mnogougao");
        drawerItem[3]=new ObjectDrawerItem(R.drawable.circle, "Krug");

        // Pass the folderData to our ListView adapter
        DrawerItemCustomAdapter adapter = new DrawerItemCustomAdapter(this, 
                R.layout.drawer_layout, drawerItem);

        // Set the adapter for the list view
        mDrawerList.setAdapter(adapter);

        // set the item click listener
        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());

        // for app icon control for nav drawer
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerToggle = new ActionBarDrawerToggle(
                this,                  /* host Activity */
                mDrawerLayout,         /* DrawerLayout object */
                R.drawable.ic_drawer,  /* nav drawer icon to replace 'Up' caret */
                R.string.drawer_open,  /* "open drawer" description */
                R.string.drawer_close  /* "close drawer" description */
                ) {

            /** Called when a drawer has settled in a completely closed state. */
            public void onDrawerClosed(View view) {
                super.onDrawerClosed(view);
                getActionBar().setTitle(mTitle);
            }

            /** Called when a drawer has settled in a completely open state. */
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
                getActionBar().setTitle(mDrawerTitle);
            }
        };

        // Set the drawer toggle as the DrawerListener
        mDrawerLayout.setDrawerListener(mDrawerToggle);

        // enable ActionBar app icon to behave as action to toggle nav drawer
        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);

        if (savedInstanceState == null) {
            // on first time display view for first nav item
            selectItem(0);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        // The action bar home/up action should open or close the drawer.
        // ActionBarDrawerToggle will take care of this.
       if (mDrawerToggle.onOptionsItemSelected(item)) {
           return true;
       }

       return super.onOptionsItemSelected(item);
    }

    // to change up caret
    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    // navigation drawer click listener
    private class DrawerItemClickListener implements ListView.OnItemClickListener {

        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            selectItem(position);
        }
    }

    private void selectItem(int position) {

        // update the main content by replacing fragments

       // Fragment fragment = null;

        switch (position) {
        case 0:
            Intent intent = new Intent(this,TriangleActivity.class);

            startActivity(intent);

        break;
        case 1:
            break;
        case 2:
            break;
        case 3:
            break;
        default:
            break;
        }
        /*
        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();*/

            // update selected item and title, then close the drawer
           /* mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(mNavigationDrawerItemTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);*/
    }

       /* } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        }
    }*/

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(mTitle);
    }
}

这是三角活动：

public class TriangleActivity extends FragmentActivity implements ActionBar.TabListener {

    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;

    private String []tabs={"Slika","Povrsina","Obim"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.acitivity_triangle);

        getActionBar().setDisplayHomeAsUpEnabled(true);

        viewPager=(ViewPager) findViewById(R.id.pager);
        actionBar=getActionBar();
        mAdapter=new TabsPagerAdapter(getSupportFragmentManager());

        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(true);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        actionBar.setHomeButtonEnabled(true);

        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name).setTabListener(this));
        }
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);
            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) {
                // TODO Auto-generated method stub
            }

            @Override
            public void onPageScrollStateChanged(int arg0) {
                // TODO Auto-generated method stub
            }
        });
    }

    private ActionBar getSupprtActionBar() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        viewPager.setCurrentItem(tab.getPosition());

    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub
        }


    public boolean onOptionsItemSelected(MenuItem item) {

        if (item.getItemId()==android.R.id.home) {
            finish();
    }
     return super.onOptionsItemSelected(item);
}
    }

这是我的 AndroidManifest：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.example.androidsdk.demo"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="21" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppBaseTheme" >
        <activity
            android:name="org.example.androidsdk.demo.MainActivity"
            android:label="@string/app_name"

            android:configChanges="orientation|screenSize" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity android:name=".TriangleActivity">

        </activity>
    </application>

</manifest> 

if (savedInstanceState == null) {
        // on first time display view for first nav item
        selectItem(0);
    }

这对我来说看起来很奇怪。我猜当你的 Activity 第一次加载时，savedInstanceState为空，因此您会自动选择导航菜单中的第一项，即TriangleActivity班级。删除上面的代码部分，看看会发生什么。