java - Activity 开始时加载 fragment

Question

我正在按照一个博客中的教程来创建 fragment 。我创建了三个 fragment ，但是当 Mainactivity 加载时......它是空的，并且只有当单击抽屉菜单中的任何项目时，才会加载 fragment 。 我想在开始时加载任何 fragment [考虑 ConnectFragment ]。

这是我的代码

public class MainActivity extends AppCompatActivity {

    private String[] mNavigationDrawerItemTitles;
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
    Toolbar toolbar;
    private CharSequence mDrawerTitle;
    private CharSequence mTitle;
    android.support.v7.app.ActionBarDrawerToggle mDrawerToggle;
    Fragment fragment = null;

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



        mTitle = mDrawerTitle = getTitle();
        mNavigationDrawerItemTitles= getResources().getStringArray(R.array.navigation_drawer_items_array);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

        setupToolbar();
        fragment = new ConnectFragment();


        DataModel[] drawerItem = new DataModel[3];

        drawerItem[0] = new DataModel(R.drawable.connect, "Connect");
        drawerItem[1] = new DataModel(R.drawable.fixtures, "Fixtures");
        drawerItem[2] = new DataModel(R.drawable.table, "Table");
        getSupportActionBar().setDisplayHomeAsUpEnabled(false);
        getSupportActionBar().setHomeButtonEnabled(true);

        DrawerItemCustomAdapter adapter = new DrawerItemCustomAdapter(this, R.layout.list_view_item_row, drawerItem);
        mDrawerList.setAdapter(adapter);
        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerLayout.setDrawerListener(mDrawerToggle);
        setupDrawerToggle();


    }


    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) {


        switch (position) {
            case 0:
                fragment = new ConnectFragment();
                break;
            case 1:
                fragment = new FixturesFragment();
                break;
            case 2:
                fragment = new TableFragment();
                break;

            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(mNavigationDrawerItemTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        if (mDrawerToggle.onOptionsItemSelected(item)) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

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

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        mDrawerToggle.syncState();
    }

    void setupToolbar(){
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
    }

    void setupDrawerToggle(){
        mDrawerToggle = new android.support.v7.app.ActionBarDrawerToggle(this,mDrawerLayout,toolbar,R.string.app_name, R.string.app_name);
        //This is necessary to change the icon of the Drawer Toggle upon state change.
        mDrawerToggle.syncState();
    }

}

我尝试过

            fragment = new ConnectFragment();

但它仍然无法在启动时加载。

提前致谢。

Answer 1

不需要在 onCreate 中创建 fragment 实例，您可以删除以下行

fragment = new ConnectFragment();

简单地说，您应该在 onCreate() 中调用 selectItem() 方法，如下所示。

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // .....
        setupDrawerToggle();
        // here you need call selectItem() method 
        selectItem(0) // you can change default fragment by changing parameter (0/1/2) as you want
    }