正确使用 OnClickListener Android

Question

我是 Android 开发的新手，我正在尝试使用 Tabs 的简单程序..

MainActivity.java

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

    Button b1 = (Button)findViewById(R.id.b1);
    b1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Toast.makeText(getApplicationContext(),"Done", Toast.LENGTH_LONG).show();
        }
    });


    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

}


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

@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;
    }

    if(id == R.id.search)
    {
        Toast.makeText(getApplicationContext(),"You tapped on SEARCH !", Toast.LENGTH_LONG).show();
    }

    return super.onOptionsItemSelected(item);
}


/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class below).
        return PlaceholderFragment.newInstance(position + 1);
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
            case 0:
                return getString(R.string.title_section1).toUpperCase(l);
            case 1:
                return getString(R.string.title_section2).toUpperCase(l);
            case 2:
                return getString(R.string.title_section3).toUpperCase(l);
        }
        return null;
    }
}

/**
 * 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;
    }
}

}

fragment_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment">

<EditText
    android:id="@+id/et1"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:hint="Enter your Name"/>

<EditText
    android:id="@+id/et2"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/et1"
    android:hint="Enter your ID"/>

<Button
    android:id="@+id/b1"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="Submit"
    android:layout_below="@+id/et2"/>
</RelativeLayout>

什么时候运行这个应用程序，应用程序在加载之前立即崩溃。

这开始于我在 'onCreate' 方法中添加 'OnClickListener' 代码。

请帮助我。我错过了什么？

Answer 1

我找到你了……:) 我会解释你的问题。您已将按 id 查找按钮的视图放入 activity 的 onCreate() 中。但是你的按钮位于片段的布局文件中。所以你不会在你的 activity xml 文件中找到它。

解法： 将以下代码放入 onCreateView():

Button b1 = rootView.findViewById(R.id.b1);
    b1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // your onclick code goes here
        }
    });

总之，保持原样。只需将您的 onCreateView() 更改为如下所示：

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        Button b1 = rootView.findViewById(R.id.b1);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // your onclick code goes here
            }
       });
        return rootView;
    }

Answer 2

Chintan Soni 是正确的。你的问题是由你的 b1 Button 在 main activity class 中的声明引起的。此按钮位于 "fragment_main" 布局文件中，该文件由您的 Fragment 实例化。

如果您将代码移动到 PlaceholderFragment 的 onCreateView，使其看起来像下面的代码，应用程序将运行。

请注意，我也已将 getApplicationContext() 更改为 getActivity()。

        @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        Button b1 = (Button) rootView.findViewById(R.id.b1);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(getActivity(), "Done", Toast.LENGTH_LONG).show();
            }
        });
        return rootView;
    }

要为每个选项卡显示不同的视图，您需要为每个选项卡声明不同的片段，例如FragmentOne、FragmentTwo、FragmentThree 每个都有自己的 onCreatView 方法来显示单独的布局文件。然后在您的 SectionsPagerAdapter 的 getView 方法中实现以下代码以根据 ViewPagers 位置显示每个 Fragment。

      @Override
    public Fragment getItem(int position) {
        Fragment fragment = null;
        switch (position) {
            case 0:
                fragment = new FragmentOne();
                break;
            case 1:
                fragment = new FragmentTwo();
                break;
            case 2:
                fragment = new FragmentThree();
                break;
        }
        return fragment;
    }

正确使用 OnClickListener Android

Proper usage of OnClickListener Android

java

android

android-tabs

onclicklistener