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我正在学习 android 开发教程，目前正在尝试了解 viewpager 类的工作原理。我已经在此处下载了演示应用程序，并且试图了解如何创建视图集合。

我知道有一个常数 NUM_PAGES 设置生成的视图数。我希望在应用程序的入口点找到一个循环或创建价值 NUM_PAGES 个视图的东西，但我找不到任何东西——这让我发疯。

我想要解决的是如何将 5 个视图添加到 ViewPager。它是如何完成的？

这是MainActivity.java文件：

/*
 * Copyright 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.animationsdemo;

import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

/**
 * The launchpad activity for this sample project. This activity launches other activities that
 * demonstrate implementations of common animations.
 */
public class MainActivity extends ListActivity {
    /**
     * This class describes an individual sample (the sample title, and the activity class that
     * demonstrates this sample).
     */
    private class Sample {
        private CharSequence title;
        private Class<? extends Activity> activityClass;

        public Sample(int titleResId, Class<? extends Activity> activityClass) {
            this.activityClass = activityClass;
            this.title = getResources().getString(titleResId);
        }

        @Override
        public String toString() {
            return title.toString();
        }
    }

    /**
     * The collection of all samples in the app. This gets instantiated in {@link
     * #onCreate(android.os.Bundle)} because the {@link Sample} constructor needs access to {@link
     * android.content.res.Resources}.
     */
    private static Sample[] mSamples;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Instantiate the list of samples.
        mSamples = new Sample[]{
                new Sample(R.string.title_crossfade, CrossfadeActivity.class),
                new Sample(R.string.title_card_flip, CardFlipActivity.class),
                new Sample(R.string.title_screen_slide, ScreenSlideActivity.class),
                new Sample(R.string.title_zoom, ZoomActivity.class),
                new Sample(R.string.title_layout_changes, LayoutChangesActivity.class),
        };

        setListAdapter(new ArrayAdapter<Sample>(this,
                android.R.layout.simple_list_item_1,
                android.R.id.text1,
                mSamples));
    }

    @Override
    protected void onListItemClick(ListView listView, View view, int position, long id) {
        // Launch the sample associated with this list position.
        startActivity(new Intent(MainActivity.this, mSamples[position].activityClass));
    }
}

这是ScreenSlideActivity.java文件：

/*
 * Copyright 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.animationsdemo;

import android.app.Fragment;
import android.app.FragmentManager;
import android.content.Intent;
import android.os.Bundle;
import android.support.v13.app.FragmentStatePagerAdapter;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.NavUtils;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.Menu;
import android.view.MenuItem;

/**
 * Demonstrates a "screen-slide" animation using a {@link ViewPager}. Because {@link ViewPager}
 * automatically plays such an animation when calling {@link ViewPager#setCurrentItem(int)}, there
 * isn't any animation-specific code in this sample.
 *
 * <p>This sample shows a "next" button that advances the user to the next step in a wizard,
 * animating the current screen out (to the left) and the next screen in (from the right). The
 * reverse animation is played when the user presses the "previous" button.</p>
 *
 * @see ScreenSlidePageFragment
 */
public class ScreenSlideActivity extends FragmentActivity {
    /**
     * The number of pages (wizard steps) to show in this demo.
     */
    private static final int NUM_PAGES = 5;

    /**
     * The pager widget, which handles animation and allows swiping horizontally to access previous
     * and next wizard steps.
     */
    private ViewPager mPager;

    /**
     * The pager adapter, which provides the pages to the view pager widget.
     */
    private PagerAdapter mPagerAdapter;

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

        // Instantiate a ViewPager and a PagerAdapter.
        mPager = (ViewPager) findViewById(R.id.pager);
        mPagerAdapter = new ScreenSlidePagerAdapter(getFragmentManager());
        mPager.setAdapter(mPagerAdapter);
        mPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                // When changing pages, reset the action bar actions since they are dependent
                // on which page is currently active. An alternative approach is to have each
                // fragment expose actions itself (rather than the activity exposing actions),
                // but for simplicity, the activity provides the actions in this sample.
                invalidateOptionsMenu();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);
        getMenuInflater().inflate(R.menu.activity_screen_slide, menu);

        menu.findItem(R.id.action_previous).setEnabled(mPager.getCurrentItem() > 0);

        // Add either a "next" or "finish" button to the action bar, depending on which page
        // is currently selected.
        MenuItem item = menu.add(Menu.NONE, R.id.action_next, Menu.NONE,
                (mPager.getCurrentItem() == mPagerAdapter.getCount() - 1)
                        ? R.string.action_finish
                        : R.string.action_next);
        item.setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM | MenuItem.SHOW_AS_ACTION_WITH_TEXT);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                // Navigate "up" the demo structure to the launchpad activity.
                // See http://developer.android.com/design/patterns/navigation.html for more.
                NavUtils.navigateUpTo(this, new Intent(this, MainActivity.class));
                return true;

            case R.id.action_previous:
                // Go to the previous step in the wizard. If there is no previous step,
                // setCurrentItem will do nothing.
                mPager.setCurrentItem(mPager.getCurrentItem() - 1);
                return true;

            case R.id.action_next:
                // Advance to the next step in the wizard. If there is no next step, setCurrentItem
                // will do nothing.
                mPager.setCurrentItem(mPager.getCurrentItem() + 1);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A simple pager adapter that represents 5 {@link ScreenSlidePageFragment} objects, in
     * sequence.
     */
    private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
        public ScreenSlidePagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            return ScreenSlidePageFragment.create(position);
        }

        @Override
        public int getCount() {
            return NUM_PAGES;
        }
    }
}

最后，这里是 ScreenSlidePageFragment.java 文件：

/*
 * Copyright 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.animationsdemo;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

/**
 * A fragment representing a single step in a wizard. The fragment shows a dummy title indicating
 * the page number, along with some dummy text.
 *
 * <p>This class is used by the {@link CardFlipActivity} and {@link
 * ScreenSlideActivity} samples.</p>
 */
public class ScreenSlidePageFragment extends Fragment {
    /**
     * The argument key for the page number this fragment represents.
     */
    public static final String ARG_PAGE = "page";

    /**
     * The fragment's page number, which is set to the argument value for {@link #ARG_PAGE}.
     */
    private int mPageNumber;

    /**
     * Factory method for this fragment class. Constructs a new fragment for the given page number.
     */
    public static ScreenSlidePageFragment create(int pageNumber) {
        ScreenSlidePageFragment fragment = new ScreenSlidePageFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_PAGE, pageNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public ScreenSlidePageFragment() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPageNumber = getArguments().getInt(ARG_PAGE);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout containing a title and body text.
        ViewGroup rootView = (ViewGroup) inflater
                .inflate(R.layout.fragment_screen_slide_page, container, false);

        // Set the title view to show the page number.
        ((TextView) rootView.findViewById(android.R.id.text1)).setText(
                getString(R.string.title_template_step, mPageNumber + 1));

        return rootView;
    }

    /**
     * Returns the page number represented by this fragment object.
     */
    public int getPageNumber() {
        return mPageNumber;
    }
}

谢谢

4

2 回答 2

0

我想知道自己关于NUM_PAHES常量以及它的使用位置。我深入挖掘并为我的项目实现了一个带有真实数据的用例，如下所示。我为mTranslationObjectsArrayList 中的片段收集数据，这样我就可以获得寻呼机适配器中给定位置所需的确切对象。

public class TrainerActivity extends ActionBarActivity {

/**
 * The pager widget, which handles animation and allows swiping horizontally to access previous
 * and next wizard steps.
 */
private ViewPager mPager;

/**
 * The pager adapter, which provides the pages to the view pager widget.
 */
private PagerAdapter mPagerAdapter;

private List<TranslationObject> mTranslationObjects = new ArrayList<TranslationObject>();


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

    fillTrainerData();

    // Instantiate a ViewPager and a PagerAdapter.
    mPager = (VerticalViewPager) findViewById(R.id.pager);
    mPagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
    mPager.setAdapter(mPagerAdapter);
}

private void fillTrainerData() {
    // putting objects in mTranslationObjects

    ...
    ...
    ...
}

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
    public ScreenSlidePagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        TrainerFragment trainerFragment = new TrainerFragment();
        Bundle bundle = new Bundle();
        bundle.putString(TrainerFragment.BUNDLE_ORIGINAL_WORD,  mTranslationObjects.get(position).originalWord);
        bundle.putString(TrainerFragment.BUNDLE_TRANSLATION,  mTranslationObjects.get(position).translation);
        bundle.putString(TrainerFragment.BUNDLE_WORD_CONTEXT,  mTranslationObjects.get(position).context);
        trainerFragment.setArguments(bundle);
        return trainerFragment;
    }

    @Override
    public int getCount() {
        return mTranslationObjects.size();
    }
}
}
于 2015-04-29T08:41:26.467 回答
0 
    public Fragment getItem(int position) {
        return ScreenSlidePageFragment.create(position);
    }

这是创建片段的地方（每个片段都包含一个视图）。

于 2012-11-23T16:47:59.117 回答