Question

我正在尝试将FragmentStatePagerAdapter与ViewPager一起使用来实现顺序幻灯片滚动视图（类似于大多数pdf阅读器）。但是，在运行代码时，会发生以下情况：

当活动变得可见时，第一页将使用不同的（第二）页面值进行实例化。但是，当滚动到其他页面然后返回到第1页时，页面将显示布局文件中的默认文本。
只有第二页和第二页到最后一页使用传递的值进行实例化（也可以使用其他页面中的值，而不是自己的值）。其余页面显示布局文件中的默认文本。

在调试时，我注意到当ViewPager.populate（）调用ViewPager.addNewItem（）时，index / currentItemNumber会发生变化。更奇怪的是，在TextView（片段布局的一部分）上调用了setText（），但文本不会从默认文本中更改。

我错过了什么吗？

以下是代码：

MainActivity.java

public class MainActivity extends ActionBarActivity implements View.OnClickListener {

private ViewPager mPager;
private Button mButtonFirst;
private Button mButtonPrev;
private Button mButtonGoTo;
private Button mButtonNext;
private Button mButtonLast;
private TextView mPageCount;
private EditText mPageNumber;
private TextView mError;
private int mNumScreens;
private int mCurrScreen;
private MyPagerAdapter mMyPagerAdapter;

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

private void setUpViews() {
    mPager = (ViewPager) findViewById(R.id.my_pager);

    // Get other view handles...

    mError = (TextView) findViewById(R.id.error_details);
}


private void setUpListeners() {
    // Set this class as click handler for all buttons
}

private void setUpPager() {

    String[] strings = new String[] {
            "1",
            "2",
            "3",
            "4",
            "5",
            "6"
        };

    // Success!
    // Set adapter and update views
    mMyPagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), strings);
    mPager.setAdapter(mMyPagerAdapter);
    mNumScreens = strings.length;
    mPageCount.setText("/" + Integer.toString(mNumScreens));
    mCurrScreen = -1;
    GoToScreen(1);
}

@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();

    // Handle options

    return super.onOptionsItemSelected(item);
}

@Override
public void onClick(View v) {
    switch(v.getId()) {
        case R.id.button_first:
            GoToScreen(1);
            break;
        case R.id.button_prev:
            GoToScreen(mCurrScreen - 1);
            break;
        case R.id.button_goto:
        {
            int screen;
            boolean reset = false;
            try {
                screen = Integer.parseInt(mPageNumber.getText().toString());
                reset = !SetToScreen(screen);
            } catch (NumberFormatException e) {
                e.printStackTrace();
                reset = true;
            }
            if(reset) {
                mPageNumber.setText(Integer.toString(mCurrScreen));
            }
        }
        break;
        case R.id.button_next:
            GoToScreen(mCurrScreen + 1);
            break;
        case R.id.button_last:
            GoToScreen(mNumScreens);
            break;
    }
}

private void GoToScreen(int screen) {
    if(SetToScreen(screen)) {
        mPageNumber.setText(Integer.toString(mCurrScreen));
    }
}

private boolean SetToScreen(int screen) {

    // Switch to a valid screen
    if(screen >= 1 && screen <= mNumScreens && mCurrScreen != screen) {
        mPager.setCurrentItem(screen - 1, false);


        // Handle button visibility

        // Update current screen
        mCurrScreen = screen;

        return true;
    }

    return false;
}

MyPagerAdapter.java

public class MyPagerAdapter extends FragmentStatePagerAdapter {

private final String[] mStrings;

public MyPagerAdapter(FragmentManager fm, String[] strings) {
    super(fm);
    mStrings = strings;
}

@Override
public int getCount() {
    return mStrings.length;
}

@Override
public Fragment getItem(int position) {
    return ScreenFragment.newInstance(mStrings[position]);
}
}

ScreenFragment.java

public class ScreenFragment extends Fragment {
private static final String ARG_SCREEN_STRING= "screen_string";

private String mScreenInfo;
private TextView mStatementLabel;


public static ScreenFragment newInstance(String screenString) {
    ScreenFragment fragment = new ScreenFragment();
    Bundle args = new Bundle();
    args.putString(ARG_SCREEN_STRING, screenString);
    fragment.setArguments(args);
    return fragment;
}

public ScreenFragment() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mScreenInfo = getArguments().getString(ARG_SCREEN_STRING);
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_screen, container, false);
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    setUpViews();
    setUpFields();
}

private void setUpFields() {
    mStatementLabel.setText(mScreenInfo);
}

private void setUpViews() {
    mStatementLabel = (TextView) getActivity().findViewById(R.id.qnr_screen_statement);
}

}

Answer 1

当我从onActivityCreated（）调用setUpViews（）和setUpFields（）到onCreateView（）时，问题解决了，几乎没有任何修改。这就是新的onCreateView（）的样子（我在这里移动了上述函数的内容）

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.fragment_screen, container, false);
    mStatementLabel = (TextView) v.findViewById(R.id.qnr_screen_statement);
    mStatementLabel.setText(mScreenInfo);
    return v;
}

我还没弄清楚为什么会导致这个问题。如果我找到任何东西，将会更新。

FragmentStatePagerAdapter和ViewPager：Fragments实例化乱序

1 个答案: