Question

我一直试图让2个片段与ViewPager一起工作但没有成功。这是包含ViewPager的Main FragmentActivity：

public class DownloadCenter extends android.support.v4.app.FragmentActivity {
    @Override
    protected void onCreate(Bundle arg0) {
        super.onCreate(arg0);
        setContentView(R.layout.download_center);
        ViewPager vp = (ViewPager) findViewById(R.id.DownloadCenter_viewPager);
        vp.setAdapter(new myAdapter(getSupportFragmentManager()));



    }

    public class myAdapter extends FragmentPagerAdapter {
        public myAdapter(FragmentManager fm) {
            super(fm);
        }

        Fragment[] fragmentArray = { Fragment.instantiate(DownloadCenter.this, Download_ImageQuality.class.getName()),
                Fragment.instantiate(DownloadCenter.this, Download_Tilawat.class.getName()) };

        @Override
        public Fragment getItem(int arg0) {
            return fragmentArray[arg0];
        }

        @Override
        public int getCount() {
            return fragmentArray.length;
        }


    }
}

这是logcat：

08-24 18:42:34.238: E/AndroidRuntime(4205): FATAL EXCEPTION: main
08-24 18:42:34.238: E/AndroidRuntime(4205): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.test/test.test.DownloadCenter}: java.lang.ClassCastException: test.test.Download_ImageQuality cannot be cast to android.support.v4.app.Fragment
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2079)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2104)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.ActivityThread.access$600(ActivityThread.java:132)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1157)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.os.Looper.loop(Looper.java:137)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.ActivityThread.main(ActivityThread.java:4575)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at java.lang.reflect.Method.invokeNative(Native Method)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at java.lang.reflect.Method.invoke(Method.java:511)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at dalvik.system.NativeStart.main(Native Method)
08-24 18:42:34.238: E/AndroidRuntime(4205): Caused by: java.lang.ClassCastException: test.test.Download_ImageQuality cannot be cast to android.support.v4.app.Fragment
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.support.v4.app.Fragment.instantiate(Fragment.java:388)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.support.v4.app.Fragment.instantiate(Fragment.java:363)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at test.test.DownloadCenter$myAdapter.<init>(DownloadCenter.java:29)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at test.test.DownloadCenter.onCreate(DownloadCenter.java:18)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.Activity.performCreate(Activity.java:4465)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
08-24 18:42:34.238: E/AndroidRuntime(4205):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2033)
08-24 18:42:34.238: E/AndroidRuntime(4205):     ... 11 more

Download_ImageQuality标题：

public class Download_ImageQuality extends android.support.v4.app.FragmentActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.download_imagequality);
                 .... //REST OF CLASS
        }
}

Answer 1

Download_ImageQuality必须是Fragment，而不是FragmentActivity。

Answer 2

我们可以阅读documentation以下内容：

ViewPager最常与Fragment一起使用，这是一个提供和管理每个页面生命周期的便捷方式。那里是使用片段的标准适配器 ViewPager，涵盖了最常见的用例。这些是 FragmentPagerAdapter，FragmentStatePagerAdapter，FragmentPagerAdapter，和FragmentStatePagerAdapter;这些类中的每一个都有简单的代码展示如何使用它们构建完整的用户界面。

正如你所看到的那样，它讨论的是Fragments而不是FragmentActivities，它们之间的主要区别在于Fragment是FragmentActivity中的一个片段。您可以将它们视为：

FragmentActivity =活动

片段=查看

注意：不完全是这样，这只是一个近似值，使其更清晰。

因此，在这种情况下，最好的方法是使用FragmentPagerAdapter并使ViewPager的所有内容成为片段，并且您可以处理每个页面内的整个生命周期。

使用带FragmentActivities的ViewPager时出现ClassCastException

2 个答案: