FragmentTransaction无法解析add()

Question

基本上，我试图以编程方式创建片段，这些片段将显示从数据库读取的列表视图。我遵循本教程(http://www.intertech.com/Blog/programmatically-working-with-android-fragments/)学习如何做这样的事情，我遇到了一个问题，我有。当使用fragmentTransaction时，Android找不到符号add()。这是我的代码：

package com.example.morgan.dynamicnews;

import android.app.Activity;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;

public class MainActivity extends AppCompatActivity

    implements NavigationDrawerFragment.NavigationDrawerCallbacks {

/**
 * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

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

    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(
            R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}



public void onSectionAttached(int number) {
    switch (number) {
        case 1:
            mTitle = getString(R.string.title_section1);
            break;
        case 2:
            mTitle = getString(R.string.title_section2);
            break;
        case 3:
            mTitle = getString(R.string.title_section3);
            break;
        case 4:
            mTitle = getString(R.string.title_section4);
            break;
        case 5:
            mTitle = getString(R.string.title_section5);
            break;

    }
}

public void restoreActionBar() {
    ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setTitle(mTitle);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Only show items in the action bar relevant to this screen
        // if the drawer is not showing. Otherwise, let the drawer
        // decide what to show in the action bar.
        getMenuInflater().inflate(R.menu.main, menu);
        restoreActionBar();
        return true;
    }
    return super.onCreateOptionsMenu(menu);
}

@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);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    /**
     * Returns a new instance of this fragment for the given section
     * number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((MainActivity) activity).onSectionAttached(
                getArguments().getInt(ARG_SECTION_NUMBER));
    }
}


public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    Fragment fragment;
    FragmentManager fragmentManager = getSupportFragmentManager();
    switch(position) {
        default:
        case 0:
            fragment = new FirstFragment();
            break;
        case 1:
            fragment = new SecondFragment();
            break;
        case 2:
            fragment = new ThirdFragment();
            break;
        case 3:
            fragment = new ForthFragment();
            break;
        case 4:
            fragment = new FifthFragment();
            break;
    }
    fragmentManager.beginTransaction()
            .replace(R.id.container, fragment)
            .commit();
}


android.app.FragmentManager fragmentManager = getFragmentManager();
android.app.FragmentTransaction fragmentTransaction =            fragmentManager.beginTransaction();

fragmentTransaction.add();
}

下面是一篇关于正在发生的事情的Imgur上传：http://imgur.com/xPLPctL

谢谢你的进阶。摩根。

Answer 1

第1期

您使用了add的错误签名。

从文件

public abstract FragmentTransaction add (int containerViewId, Fragment fragment)

将片段添加到活动状态。此片段还可以选择将其视图(如果Fragment.onCreateView返回非空)插入到活动的容器视图中。使用空标记调用add(int、片段、字符串)。

参数

containerViewId     int

fragment            Fragment

所以你的代码应该是

fragmentTransaction.add(R.id.container, new MyFragment()); // Change layout and Fragment class here

第2期

整个代码是方法之外的，甚至是不正确的类。将此代码移动到任何方法中。每一行代码都应该在任何方法下(显然，变量声明可以在类中的任何地方)。

Answer 2

你少了两个论点。第一个是片段占位符的id，第二个是片段本身。它基本上采用与替换调用相同的参数。

Answer 3

.add()将至少采用两个论点。参考文献