操作栏主页按钮崩溃，而后退按钮工作

Question

我在这件事上完全被难住了。我有一个活动C，当我试着按下后退按钮时，它工作了。但是，当我使用操作栏中的home/up按钮时，它就会崩溃（请参见下面的错误）。下面是我的代码中处理备份/备份按钮的部分。

活动C：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_offline_viewer);
    ActionBar actionBar = getActionBar();
    actionBar.setDisplayHomeAsUpEnabled(true);
}

    @Override
public boolean onPrepareOptionsMenu(Menu menu) {
    if(!isOnline) {
        menu.removeItem(R.id.saveRoute);
    }
    return true;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.offline_viewer, menu);
    return true;
}

@Override
public void onBackPressed() {
    super.onBackPressed(); 
    finish();
} 

@Override
public boolean onOptionsItemSelected(MenuItem item)
{       
    //Get names for saving
    String[] startParts = onlineFrom.split(",");
    String startName = startParts[0] + "," + startParts[1]; 
    String[] endParts = onlineTo.split(",");
    String endName = endParts[0] + "," + endParts[1]; 
    System.out.println(item.getItemId());
    switch(item.getItemId()){
    //Save xml file or route once pressed
    case R.id.saveRoute:
        //TODO:Uncomment once server is ready
        new DownloadFileFromURL(this, startName, endName).execute(urlForDownload);
        return true;       
    case android.R.id.home: 
        System.out.println(item.getItemId());
        onBackPressed();
        return true;
    }

    return super.onOptionsItemSelected(item);
}

错误：

08-22 16:15:43.629: W/dalvikvm(4908): threadid=1: thread exiting with uncaught exception     (group=0x41c7e888)
08-22 16:15:43.634: E/AndroidRuntime(4908): FATAL EXCEPTION: main
08-22 16:15:43.634: E/AndroidRuntime(4908): java.lang.NullPointerException
08-22 16:15:43.634: E/AndroidRuntime(4908):     at     com.example.otpxmlgetter.OfflineViewer.onOptionsItemSelected(OfflineViewer.java:185)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.app.Activity.onMenuItemSelected(Activity.java:2590)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:361)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at com.android.internal.widget.ActionBarView$3.onClick(ActionBarView.java:167)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.view.View.performClick(View.java:4204)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.view.View$PerformClick.run(View.java:17354)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.os.Handler.handleCallback(Handler.java:725)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.os.Handler.dispatchMessage(Handler.java:92)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.os.Looper.loop(Looper.java:137)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at android.app.ActivityThread.main(ActivityThread.java:5232)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at java.lang.reflect.Method.invokeNative(Native Method)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at java.lang.reflect.Method.invoke(Method.java:511)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:561)
08-22 16:15:43.634: E/AndroidRuntime(4908):     at dalvik.system.NativeStart.main(Native Method)

这是否与到达活动C有两种可能的方式有关？要么是-

Answer 1

通常不建议调用活动生命周期方法。框架使用的onwhich方法。如果你想完成活动，而不是使用。。。

this.finish()

或

getActivity.finish()

如果您处于片段上下文中。

p. s：onBackPmed实际上是工作的（反对这个答案的初始假设）。有关此问题的根本原因，请参阅下面的评论。

P. S.：这篇文章提出了this.dispatch关键事件（新的关键事件（关键事件。ACTION_DOWN，关键事件。KEYCODE_BACK））；作为替代