我做了一个简单的Android活动,它有一个操作栏,可以在两个片段之间切换。
在我转动设备之前一切正常。事实上,当我旋转时,我得到了2个片段,一个在另一个上面:前一个活跃的片段和第一个片段。
为什么?
如果旋转破坏并重新创建我的活动,为什么我会获得2个碎片?
样本代码:
活动

package rb.rfrag.namespace;

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.Activity;
import android.os.Bundle;

    public class RFragActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Notice that setContentView() is not used, because we use the root
        // android.R.id.content as the container for each fragment

     // setup action bar for tabs
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        //actionBar.setDisplayShowTitleEnabled(false);

        Tab tab;
        tab = actionBar.newTab()
                .setText(R.string.VarsTab)
                .setTabListener(new TabListener<VarValues>(
                        this, "VarValues", VarValues.class));
        actionBar.addTab(tab);

        tab = actionBar.newTab()
                .setText(R.string.SecTab)
                .setTabListener(new TabListener<SecFrag>(
                        this, "SecFrag", SecFrag.class));
        actionBar.addTab(tab);
    }
}

Tablistener公司
package rb.rfrag.namespace;

import android.app.ActionBar;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.app.ActionBar.Tab;

public class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private Fragment mFragment;
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    /** Constructor used each time a new tab is created.
      * @param activity  The host Activity, used to instantiate the fragment
      * @param tag  The identifier tag for the fragment
      * @param clz  The fragment's Class, used to instantiate the fragment
      */
    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
    }

    /* The following are each of the ActionBar.TabListener callbacks */

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // Check if the fragment is already initialized
        if (mFragment == null) {
            // If not, instantiate and add it to the activity
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);
        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            // Detach the fragment, because another one is being attached
            ft.detach(mFragment);
        }
    }
}

最佳答案

我已经解决了在活动中使用onSaveInstanceStateonRestoreInstanceState来维护所选选项卡和修改onTabSelected的问题,如下所示。
最后一次修改避免了Android重建它没有破坏的片段。但是,我不明白为什么当当前片段号(您对此有什么想法吗?)

public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // previous Fragment management
        Fragment prevFragment;
        FragmentManager fm = mActivity.getFragmentManager();
        prevFragment = fm.findFragmentByTag(mTag);
        if (prevFragment != null) {
            mFragment = prevFragment;
        } // \previous Fragment management

        // Check if the fragment is already initialized
        if (mFragment == null) {
            // If not, instantiate and add it to the activity
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);
        }
    }

07-24 09:46
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