java - 调用onOptionsItemSelected时出现空指针异常

Question

java代码如下:布局看起来不错。当我单击左上角的导航栏图标时，似乎唯一的问题出现了。

package com.example.chirag.carparlour;

import android.app.ActionBar;
import android.content.Intent;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.view.Menu;


public class MainActivity extends AppCompatActivity {
private DrawerLayout dl;
private ActionBarDrawerToggle abdt;

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

    Button book = (Button)findViewById(R.id.book);
    Button sub = (Button)findViewById(R.id.sub);
    Button offers = (Button)findViewById(R.id.offers);
    Button support = (Button)findViewById(R.id.support);
    Button comp = (Button)findViewById(R.id.comp);

    DrawerLayout dl = (DrawerLayout)findViewById(R.id.drawerlayout);
    ActionBarDrawerToggle abdt = new ActionBarDrawerToggle(this, dl , R.string.Open, R.string.Close);

    dl.addDrawerListener(abdt);
    abdt.syncState();
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);





    book.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(MainActivity.this, bookawash.class);
            startActivity(intent);
        }
    });

    sub.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(MainActivity.this, subscriptions.class);
            startActivity(intent);
        }
    });


    offers.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

        }
    });


    support.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

        }
    });


    comp.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

        }
    });

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if(abdt.onOptionsItemSelected(item))
    {return true;}


    return super.onOptionsItemSelected(item);
}}

并且日志中报错如下:

   FATAL EXCEPTION: main
              Process: com.example.chirag.carparlour, PID: 4879
              java.lang.NullPointerException: Attempt to invoke virtual            method 'boolean android.support.v7.app.ActionBarDrawerToggle.onOptionsItemSelected(android.view.MenuItem)' on a null object reference
                  at com.example.chirag.carparlour.MainActivity.onOptionsItemSelected(MainActivity.java:86)
                  at android.app.Activity.onMenuItemSelected(Activity.java:2914)
                  at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:408)
                  at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:198)
                  at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:113)
                  at android.support.v7.widget.ToolbarWidgetWrapper$1.onClick(ToolbarWidgetWrapper.java:187)
                  at android.view.View.performClick(View.java:5205)
                  at android.view.View$PerformClick.run(View.java:21166)
                  at android.os.Handler.handleCallback(Handler.java:739)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:5422)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

每当我单击左上角的导航图标时，应用程序就会崩溃并显示此错误。如果你只是滑动屏幕，它就可以正常工作。当我没有这种方法时，应用程序不会崩溃，但导航栏也不会显示。这在以前从未发生过。

求助!

Answer 1

我认为问题是这样的:(在 onCreate 中):

ActionBarDrawerToggle abdt = new ActionBarDrawerToggle(this, dl , R.string.Open, R.string.Close);

切换到:

abdt = new ActionBarDrawerToggle(this, dl , R.string.Open, R.string.Close);