ViewPager Andorid:NullPointerException: 尝试调用虚拟方法
ViewPager Andorid:NullPointerException: Attempt to invoke virtual method
我有我的片段，我在 xml 文件中添加了两个滑块：
public class FilterSlider extends Fragment implements FragmentLifecycle {
private static final String TAG = FilterSlider.class.getSimpleName();
RelativeLayout relativeLayout;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.filter_slider, container, false);
return view;
}
并且 xml 文件看起来：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<SeekBar
android:id="@+id/seekBarMin"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="20dp"
android:max="100"/>
<SeekBar
android:id="@+id/seekBarMax"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="50dp"
android:max="100"/>
</RelativeLayout>
现在，当我尝试使用以下代码从主 activity 访问任何滑块时：
这是我的主要activity class:
setContentView(R.layout.activity_main);
pageAdapter = new MyPagerAdapter(getSupportFragmentManager());
final ViewPager pager = (ViewPager)findViewById(R.id.myViewPager);
pager.setAdapter(pageAdapter);
seekbarMin = (SeekBar) findViewById(R.id.seekBarMin);
seekbarMax = (SeekBar) findViewById(R.id.seekBarMax);
sliderMaxTemp = seekbarMax.getProgress();
adn 这里是 MyPageAdapter class:
private List<Fragment> fragments;
public MyPagerAdapter(FragmentManager fm) {
super(fm);
this.fragments = new ArrayList<Fragment>();
fragments.add(new FilterCheckBox());
fragments.add(new FilterRadioButton());
fragments.add(new FilterSlider());
}
它显示以下错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.widget.SeekBar.getProgress()' on a null object reference.
如果有任何解决错误的建议，我将不胜感激。
我已经在真实设备 (API10) 上进行了测试并且可以正常工作。
（重写了很多部分。使用 diff 与您的源代码进行检查。）
需要更多信息来找出问题..
// part of manifest
<uses-sdk android:minSdkVersion="10" />
//MainActivity.java
// Changed imports.
// MUST check v4 library class or not. (for each UI parts class etc.)
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.View.OnClickListener; // for selectButton_* click events.
import android.widget.SeekBar;
// Changed Activity -> FragmentActivity to use getSupportFragmentManager()
public class MainActivity extends FragmentActivity
{
private ViewPager pager;
private SeekBar seekbarMin;
private SeekBar seekbarMax;
private int sliderMaxTemp;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Init();
}
private void Init()
{
MyPagerAdapter pageAdapter = new MyPagerAdapter(getSupportFragmentManager());
pager = (ViewPager) findViewById(R.id.myViewPager);
pager.setAdapter(pageAdapter);
seekbarMin = (SeekBar) findViewById(R.id.seekBarMin);
seekbarMax = (SeekBar) findViewById(R.id.seekBarMax);
sliderMaxTemp = seekbarMax.getProgress();
// Events to choose page.
// You may want to use onTouch or gesture..
final int idx_CheckBox = 0;
final int idx_RadioButton = 1;
final int idx_Slider = 2;
findViewById(R.id.selectButton_CheckBox).setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
// Select page
pager.setCurrentItem(idx_CheckBox);
}
});
findViewById(R.id.selectButton_RadioButton).setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
pager.setCurrentItem(idx_RadioButton);
}
});
findViewById(R.id.selectButton_Slider).setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
pager.setCurrentItem(idx_Slider);
}
});
}
}
// FilterSlider.java
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
// Changed to "v4" Fragment
public class FilterSlider extends Fragment
{
private static final String TAG = FilterSlider.class.getSimpleName();
RelativeLayout relativeLayout;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.filter_slider, container, false);
return view;
}
}
// MyPagerAdapter.java
import java.util.ArrayList;
import java.util.List;
// Changed to "v4" classes
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
// Changed PagerAdapter -> FragmentStatePagerAdapter
public class MyPagerAdapter extends FragmentStatePagerAdapter
{
private List<Fragment> fragments;
MyPagerAdapter(FragmentManager fm)
{
super(fm);
this.fragments = new ArrayList<Fragment>();
fragments.add(new FilterCheckBox());
fragments.add(new FilterRadioButton());
fragments.add(new FilterSlider());
}
@Override
public int getCount()
{
return fragments.size();
}
@Override
public Fragment getItem(int position)
{
// returns fragment you want to show
try
{
return fragments.get(position);
}
catch (IndexOutOfBoundsException e)
{
// TODO: handle exception
return null;
}
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<SeekBar
android:id="@+id/seekBarMin"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="20dp"
android:max="100" />
<SeekBar
android:id="@+id/seekBarMax"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="50dp"
android:max="100" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
android:id="@+id/selectButton_CheckBox"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="CheckBox" />
<Button
android:id="@+id/selectButton_RadioButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="RadioButton" />
<Button
android:id="@+id/selectButton_Slider"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Slider" />
</LinearLayout>
<android.support.v4.view.ViewPager
android:id="@+id/myViewPager"
android:layout_width="250dp"
android:layout_height="wrap_content" />
</LinearLayout>
filter_slider.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Filter Slider"
android:textAppearance="?android:attr/textAppearanceMedium" />
</LinearLayout>
我有我的片段，我在 xml 文件中添加了两个滑块：
public class FilterSlider extends Fragment implements FragmentLifecycle {
private static final String TAG = FilterSlider.class.getSimpleName();
RelativeLayout relativeLayout;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.filter_slider, container, false);
return view;
}
并且 xml 文件看起来：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<SeekBar
android:id="@+id/seekBarMin"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="20dp"
android:max="100"/>
<SeekBar
android:id="@+id/seekBarMax"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="50dp"
android:max="100"/>
</RelativeLayout>
现在，当我尝试使用以下代码从主 activity 访问任何滑块时：
这是我的主要activity class:
setContentView(R.layout.activity_main);
pageAdapter = new MyPagerAdapter(getSupportFragmentManager());
final ViewPager pager = (ViewPager)findViewById(R.id.myViewPager);
pager.setAdapter(pageAdapter);
seekbarMin = (SeekBar) findViewById(R.id.seekBarMin);
seekbarMax = (SeekBar) findViewById(R.id.seekBarMax);
sliderMaxTemp = seekbarMax.getProgress();
adn 这里是 MyPageAdapter class:
private List<Fragment> fragments;
public MyPagerAdapter(FragmentManager fm) {
super(fm);
this.fragments = new ArrayList<Fragment>();
fragments.add(new FilterCheckBox());
fragments.add(new FilterRadioButton());
fragments.add(new FilterSlider());
}
它显示以下错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.widget.SeekBar.getProgress()' on a null object reference.
如果有任何解决错误的建议，我将不胜感激。
我已经在真实设备 (API10) 上进行了测试并且可以正常工作。 （重写了很多部分。使用 diff 与您的源代码进行检查。）
需要更多信息来找出问题..
// part of manifest
<uses-sdk android:minSdkVersion="10" />
//MainActivity.java
// Changed imports.
// MUST check v4 library class or not. (for each UI parts class etc.)
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.View.OnClickListener; // for selectButton_* click events.
import android.widget.SeekBar;
// Changed Activity -> FragmentActivity to use getSupportFragmentManager()
public class MainActivity extends FragmentActivity
{
private ViewPager pager;
private SeekBar seekbarMin;
private SeekBar seekbarMax;
private int sliderMaxTemp;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Init();
}
private void Init()
{
MyPagerAdapter pageAdapter = new MyPagerAdapter(getSupportFragmentManager());
pager = (ViewPager) findViewById(R.id.myViewPager);
pager.setAdapter(pageAdapter);
seekbarMin = (SeekBar) findViewById(R.id.seekBarMin);
seekbarMax = (SeekBar) findViewById(R.id.seekBarMax);
sliderMaxTemp = seekbarMax.getProgress();
// Events to choose page.
// You may want to use onTouch or gesture..
final int idx_CheckBox = 0;
final int idx_RadioButton = 1;
final int idx_Slider = 2;
findViewById(R.id.selectButton_CheckBox).setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
// Select page
pager.setCurrentItem(idx_CheckBox);
}
});
findViewById(R.id.selectButton_RadioButton).setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
pager.setCurrentItem(idx_RadioButton);
}
});
findViewById(R.id.selectButton_Slider).setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
pager.setCurrentItem(idx_Slider);
}
});
}
}
// FilterSlider.java
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
// Changed to "v4" Fragment
public class FilterSlider extends Fragment
{
private static final String TAG = FilterSlider.class.getSimpleName();
RelativeLayout relativeLayout;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.filter_slider, container, false);
return view;
}
}
// MyPagerAdapter.java
import java.util.ArrayList;
import java.util.List;
// Changed to "v4" classes
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
// Changed PagerAdapter -> FragmentStatePagerAdapter
public class MyPagerAdapter extends FragmentStatePagerAdapter
{
private List<Fragment> fragments;
MyPagerAdapter(FragmentManager fm)
{
super(fm);
this.fragments = new ArrayList<Fragment>();
fragments.add(new FilterCheckBox());
fragments.add(new FilterRadioButton());
fragments.add(new FilterSlider());
}
@Override
public int getCount()
{
return fragments.size();
}
@Override
public Fragment getItem(int position)
{
// returns fragment you want to show
try
{
return fragments.get(position);
}
catch (IndexOutOfBoundsException e)
{
// TODO: handle exception
return null;
}
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<SeekBar
android:id="@+id/seekBarMin"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="20dp"
android:max="100" />
<SeekBar
android:id="@+id/seekBarMax"
android:layout_width="250dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="50dp"
android:max="100" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
android:id="@+id/selectButton_CheckBox"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="CheckBox" />
<Button
android:id="@+id/selectButton_RadioButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="RadioButton" />
<Button
android:id="@+id/selectButton_Slider"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Slider" />
</LinearLayout>
<android.support.v4.view.ViewPager
android:id="@+id/myViewPager"
android:layout_width="250dp"
android:layout_height="wrap_content" />
</LinearLayout>
filter_slider.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Filter Slider"
android:textAppearance="?android:attr/textAppearanceMedium" />
</LinearLayout>