android.content.res.Resources android.content.Context.getResources（）在空对象引用上

Question

我试图在SlidingTabLayout上显示图标，所以在我的适配器中创建了类似这样的内容，我在寻找教程的某个时候找到了它，所以我编辑了将使用getDrawable的部分，因为它说它已经被弃用并且应用我发现的解决方案

    @Override
public CharSequence getPageTitle(int position) {

    Drawable image = ResourcesCompat.getDrawable(mContext.getResources(), icons[position], null);
    image.setBounds(0, 0, 48, 48);
    SpannableString sb = new SpannableString(" ");
    ImageSpan imageSpan = new ImageSpan(image, ImageSpan.ALIGN_BOTTOM);
    sb.setSpan(imageSpan, 0, 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
    return sb;
}

我也在我的适配器上声明了它，我已经在这里检查是否确实将它放在可绘制对象上，并且所有这些都在那里。

  private int[] icons = {
        R.drawable.tabone,
        R.drawable.tabtwo,
        R.drawable.tabthree,
        R.drawable.tapfour,
        R.drawable.tabfive
};

我不知道我做错了什么，但我总是遇到这个错误

Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference

即使我声明一个变量来处理图像。谁能帮助我，我的最低版本为14，目标sdk为22。谢谢。

这是我的适配器代码

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

CharSequence Titles[]; 
int NumbOfTabs;

Context mContext;

private int[] icons = {
        R.drawable.tabone,
        R.drawable.tabtwo,
        R.drawable.tabthree,
        R.drawable.tapfour,
        R.drawable.tabfive
};


public ViewPagerAdapter(FragmentManager fm,CharSequence mTitles[], int mNumbOfTabsumb, Context context) {
    super(fm);

    this.Titles = mTitles;
    this.NumbOfTabs = mNumbOfTabsumb;
    this.mContext = context;

}


@Override
public Fragment getItem(int position) {

    if(position == 0) // if the position is 0 we are returning the First tab
    {
        Tabone tab_one = new Tabone();
        return tab_one;
    }
    else if(position == 1)
    {
        Tabtwo tab_two = new Tabtwo();
        return tab_two;

    }else if(position == 2){
        Tabthree tab_three = new Tabthree();
        return tab_three;
    }else if(position == 3){
        Tabfour tab_four = new Tabfour();
        return tab_four;
    }else{
        Tabfive tab_five = new Tabfive();
        return tab_five;
    }

}


@Override
public CharSequence getPageTitle(int position) {

    Drawable image = ResourcesCompat.getDrawable(mContext.getResources(), icons[position], null);
    image.setBounds(0, 0, 48, 48);
    SpannableString sb = new SpannableString(" ");
    ImageSpan imageSpan = new ImageSpan(image, ImageSpan.ALIGN_BOTTOM);
    sb.setSpan(imageSpan, 0, 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
    return sb;
}



// This method return the Number of tabs for the tabs Strip

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

}

这是我的MainActivity

private ViewPager mPager;
private ViewPagerAdapter adapter;
private SlidingTabLayout mTabs;
private Context mContext;

 CharSequence Titles[] =   {"One", "Two", "Three", "Four", "Five"};

int Numboftabs = 5;

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

    adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs, mContext);

    // Assigning ViewPager View and setting the adapter
    mPager = (ViewPager) findViewById(R.id.pager);
    mPager.setAdapter(adapter);

    // Assigning the Sliding Tab Layout View
    mTabs = (SlidingTabLayout) findViewById(R.id.tabs);
    mTabs.setDistributeEvenly(true); 


    // Setting the ViewPager For the SlidingTabsLayout
    mTabs.setSelectedIndicatorColors(getResources().getColor(R.color.tabsIndicator));
    mTabs.setViewPager(mPager);
}

Answer 1

看这里：

adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs, mContext);

从这里mContext开始null。因为您没有为方法mContext内部的变量分配任何引用onCreate。

将其更改为：

adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs, MainActivity.this);

或者你也可以试试这个：

内部onCreate方法：

mContext = MainActivity.this;

adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs, mContext);

使用以下代码ViewPagerAdapter：

public class ViewPagerAdapter extends FragmentStatePagerAdapter { 

CharSequence Titles[]; 
int NumbOfTabs;

private Activity mContext;

private int[] icons = {
        R.drawable.tabone,
        R.drawable.tabtwo,
        R.drawable.tabthree,
        R.drawable.tapfour,
        R.drawable.tabfive
}; 


public ViewPagerAdapter(FragmentManager fm,CharSequence mTitles[], int mNumbOfTabsumb, Activity context) {
    super(fm); 

    this.Titles = mTitles;
    this.NumbOfTabs = mNumbOfTabsumb;
    this.mContext = context;

} 


@Override 
public Fragment getItem(int position) {

    if(position == 0) // if the position is 0 we are returning the First tab
    { 
        Tabone tab_one = new Tabone();
        return tab_one;
    } 
    else if(position == 1)
    { 
        Tabtwo tab_two = new Tabtwo();
        return tab_two;

    }else if(position == 2){
        Tabthree tab_three = new Tabthree();
        return tab_three;
    }else if(position == 3){
        Tabfour tab_four = new Tabfour();
        return tab_map; 
    }else{ 
        Tabfive tab_five = new Tabfive();
        return tab_five;
    } 

} 


    @Override 
public CharSequence getPageTitle(int position) {
    Drawable image = mContext.getResources().getDrawable(icons[position]);
    image.setBounds(0, 0, 48, 48);
    SpannableString sb = new SpannableString(" ");
    ImageSpan imageSpan = new ImageSpan(image, ImageSpan.ALIGN_BOTTOM);
    sb.setSpan(imageSpan, 0, 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
    return sb;
}





// This method return the Number of tabs for the tabs Strip 

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