Question

我已经在这方面工作了一个星期，我无法理解。我有一个有4个视图的寻呼机适配器。它让我可以在它们之间滑动。但是当我调用onClickListener时，应用程序在启动时崩溃，因为Listener为null。我是一名新程序员，我不明白如何解决这个问题。请帮忙！我已经隔离了问题的根源，在Listener查找按钮ID之后，视图没有被创建或被销毁，这就是为什么它是null并且崩溃的原因。

方法destroyItem是我认为导致它的原因，因为当我删除它时，应用程序不会崩溃，直到我开始刷视图。

public class SplashPager extends PagerAdapter {

Button b;

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return 4;
}

@Override
public Object instantiateItem(View collection, int position) {
    LayoutInflater inflater = (LayoutInflater) collection.getContext()
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    int resId = 0;
    switch (position) {

    case 0:
        resId = R.layout.splash2;
        b = (Button) collection.findViewById(R.id.splashB);
        b.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                                    //setContentView(r.layout.someLayout);
            }
        });
        break;
    case 1:
        resId = R.layout.splash3;
        break;
    case 2:
        resId = R.layout.splash4;
        break;
    case 3:
        resId = R.layout.splash5;
        break;

    }

    View view = inflater.inflate(resId, null);
    ((ViewPager) collection).addView(view, 0);
    return view;

}

@Override
public void destroyItem(View arg0, int arg1, Object arg2) {
    // TODO Auto-generated method stub
    ((ViewPager) arg0).removeView((View) arg2);

}

@Override
public Parcelable saveState() {
    // TODO Auto-generated method stub
    return null;
}

@Override
public boolean isViewFromObject(View arg0, Object arg1) {
    // TODO Auto-generated method stub
    return arg0 == ((View) arg1);
}

}

日志：

01-17 21:03:35.179: W/dalvikvm(16226): threadid=1: thread exiting with uncaught exception (group=0x401a2560)
01-17 21:03:35.179: E/AndroidRuntime(16226): FATAL EXCEPTION: main
01-17 21:03:35.179: E/AndroidRuntime(16226): java.lang.NullPointerException
01-17 21:03:35.179: E/AndroidRuntime(16226):    at   com.example.survtest2.SplashPager.instantiateItem(SplashPager.java:33)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.PagerAdapter.instantiateItem(PagerAdapter.java:110)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:801)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:930)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:386)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at  android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at  android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewRoot.performTraversals(ViewRoot.java:844)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewRoot.handleMessage(ViewRoot.java:1864)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.os.Looper.loop(Looper.java:130)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.app.ActivityThread.main(ActivityThread.java:3733)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at java.lang.reflect.Method.invokeNative(Native Method)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at java.lang.reflect.Method.invoke(Method.java:507)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:892)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:650)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at dalvik.system.NativeStart.main(Native Method)
01-17 21:03:35.199: E/AndroidRuntime(16226): [Blue Error Handler] Make Debugging Report file for main
01-17 21:03:35.199: E/AndroidRuntime(16226): java.lang.NullPointerException
01-17 21:03:35.199: E/AndroidRuntime(16226):    at com.example.survtest2.SplashPager.instantiateItem(SplashPager.java:33)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.PagerAdapter.instantiateItem(PagerAdapter.java:110)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:801)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:930)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at  android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:386)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at  android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewRoot.performTraversals(ViewRoot.java:844)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewRoot.handleMessage(ViewRoot.java:1864)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.os.Looper.loop(Looper.java:130)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.app.ActivityThread.main(ActivityThread.java:3733)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at java.lang.reflect.Method.invokeNative(Native Method)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at    java.lang.reflect.Method.invoke(Method.java:507)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:892)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at    com.android.internal.os.ZygoteInit.main(ZygoteInit.java:650)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at     dalvik.system.NativeStart.main(Native Method)

我很确定这是问题的原因，但我不知道这种方法是如何工作的或如何解决它：

@Override
public void destroyItem(View arg0, int arg1, Object arg2) {
    // TODO Auto-generated method stub
    ((ViewPager) arg0).removeView((View) arg2);

}

我的另一个问题是如何使用该按钮加载新视图或活动？它不允许我实现活动，这是我学习如何调用bundle的唯一方法。提前谢谢！

Answer 1

尝试将destroyItem更改为：

@Override
public void destroyItem(View arg0, int arg1, Object arg2){
    ((ViewPager) arg0).removeViewAt(arg1);
}

和isViewFromObject：

@Override
public boolean isViewFromObject(View view, Object object){

    return view.equals(object); 
 }

如果这些更改不起作用，那么我建议你检查一下你可以在集合View上“findViewById”后会发生什么。看起来你看的按钮不在那个对象内。您必须在正在膨胀的视图中搜索它。

尝试使用此代码作为实例化代码：

@Override
    public Object instantiateItem(View collection, int position) {
        LayoutInflater inflater = (LayoutInflater) collection.getContext()
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        int resId = 0;
        View view = null;
        switch (position) {

        case 0:
            view = inflater.inflate(R.layout.splash2, null);
            b = (Button) view.findViewById(R.id.splashB);
            b.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                                        //setContentView(r.layout.someLayout);
                }
            });
            break;
        case 1:
            view = inflater.inflate(R.layout.splash3, null);
            break;
        case 2:
            view = inflater.inflate(R.layout.splash4, null);
            break;
        case 3:
            view = inflater.inflate(R.layout.splash5, null);
            break;

        }


        ((ViewPager) collection).addView(view, 0);
        return view;
    }

如何在寻呼机适配器中调用OnClickListener

1 个答案: