Android Navigation Drawer with multiple activites

问题:

I'm trying to to use a Navigation Drawer with a few activites and no fragments. I read me through a few answers here and ended up in this and I'v got the same Problem as the user Dediqated, here is my Code:

BaseActivity.java:

import android.app.Activity;
import android.content.res.Configuration;
import android.content.res.Resources.NotFoundException;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class BaseActivity extends Activity {

    public DrawerLayout drawerLayout;
    public ListView drawerList;
    public String[] layers;
    private ActionBarDrawerToggle drawerToggle;

    protected void onCreate(Bundle savedInstanceState) {
        try {
            // R.id.drawer_layout should be in every activity with exactly the same
            // id.
            drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

            drawerToggle = new ActionBarDrawerToggle((Activity) this, drawerLayout,
                    R.drawable.ic_drawer, 0, 0) {
                public void onDrawerClosed(View view) {
                    getActionBar().setTitle(R.string.hello_world);
                }

                public void onDrawerOpened(View drawerView) {
                    getActionBar().setTitle(R.string.hello_world);
                }
            };
            drawerLayout.setDrawerListener(drawerToggle);

            getActionBar().setDisplayHomeAsUpEnabled(true);
            getActionBar().setHomeButtonEnabled(true);

            layers = getResources().getStringArray(R.array.planets_array);
            drawerList = (ListView) findViewById(R.id.left_drawer);
            drawerList.setAdapter(new ArrayAdapter<String>(this,
                    R.layout.drawer_list_item, android.R.id.text1, layers));
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            e.printStackTrace();
            e.printStackTrace();
        }

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        if (drawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        return super.onOptionsItemSelected(item);

    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        drawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        drawerToggle.onConfigurationChanged(newConfig);
    }
}

TestActivity.java:

import android.os.Bundle;

public class TestActivity extends BaseActivity{
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_profile);
    }
}

activity_base.xml:

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- The main content view -->
    <FrameLayout
        android:id="@+id/content_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
        <!-- Add content here -->
    </FrameLayout>

    <!-- The navigation drawer -->
    <ListView android:id="@+id/left_drawer"
        android:layout_width="240dp"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:choiceMode="singleChoice"
        android:divider="@android:color/transparent"
        android:dividerHeight="0dp"
        android:background="#111"/>
</android.support.v4.widget.DrawerLayout>

activity_profile.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".ProfileActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

drawer_list_item.xml

<!--
  Copyright 2013 The Android Open Source Project

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  -->

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/text1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceListItemSmall"
    android:gravity="center_vertical"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:textColor="#fff"
    android:background="?android:attr/activatedBackgroundIndicator"
    android:minHeight="?android:attr/listPreferredItemHeightSmall"/>

In BaseActivity.java in line drawerLayout.setDrawerListener(drawerToggle); Eclipse throws a NullPointerException and I just don't get why.

I'm sorry to make an extra question for the same problem as already asked, but I'm new and not allowed to add comments.

回答1:

What you are doing can't work because you are calling findViewById before setting the contentview. This means you are trying to access elements within the Layout of your Activity before you even set the Layout or in other words, you are calling View.findViewById before initializing your View.
Also, as far as I know, you have to call super.onCreate in your Activity. You are not doing this. You call super.onCreate in your TestActivity but you have to call it in your BaseActivity.
I haven't been working with AB for several Activities, but I would suggest to do the following:

BaseActivity

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

void initDrawer(){
    // put everything you have in your onCreate in here:
    try {
        // R.id.drawer_layout should be in every activity with exactly the same
        // id.
        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

        drawerToggle = new ActionBarDrawerToggle((Activity) this, drawerLayout,
                R.drawable.ic_drawer, 0, 0) {
            public void onDrawerClosed(View view) {
                getActionBar().setTitle(R.string.hello_world);
            }

            public void onDrawerOpened(View drawerView) {
                getActionBar().setTitle(R.string.hello_world);
            }
        };
        drawerLayout.setDrawerListener(drawerToggle);

        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);

        layers = getResources().getStringArray(R.array.planets_array);
        drawerList = (ListView) findViewById(R.id.left_drawer);
        drawerList.setAdapter(new ArrayAdapter<String>(this,
                R.layout.drawer_list_item, android.R.id.text1, layers));
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        e.printStackTrace();
        e.printStackTrace();
    }

}

TestActivity

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

回答2:

The approach with the BaseActivity did not really work well with me. Reason was the mixture of Activity and Fragments and the use of the NavigationDrawerFragment which is kindly generated when creating a new project in eclipse.

I have Activity A which has a menu with 5 items. 1 item will start another activity (because it is a FragmentPagerAdaper) and the others will just switch the Fragment in Activity A.

When I use BaseActivity I would have only one onNavigationDrawerItemSelected(int) (click-event).

Using this also in Activity B causes a problem, because I need to switch back to Activity A first and then display the appropriate Fragment. This is essentially different click-handling.

I ended up solving it with having the onNavigationDrawerItemSelected(int) in both Activities. Implementing the drawer is just 2 lines, so this is not too much double work. If I had more Activities, then I would go for the BaseActivity but would require switch statement for case handling depending on the calling activity.