将导航抽屉活动扩展到其他活动

Question

I'm trying to create a navigation drawer activity so I can extend that activity and use the menu in all activities by following the answer given in this question Link but my test app keeps crashing, here's my code:

BaseActivity.java

public class BaseActivity extends Activity {

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

    protected void onCreate(Bundle savedInstanceState) {
        // 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));

    }

    @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);
    }
}

MainActivity.java

public class MainActivity extends BaseActivity {

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

}

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>

Logcat

03-03 01:22:18.031: D/AndroidRuntime(27902): Shutting down VM
03-03 01:22:18.031: W/dalvikvm(27902): threadid=1: thread exiting with uncaught exception (group=0x2b542210)
03-03 01:22:18.041: E/AndroidRuntime(27902): FATAL EXCEPTION: main
03-03 01:22:18.041: E/AndroidRuntime(27902): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.slider/com.example.slider.MainActivity}: java.lang.NullPointerException
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.os.Looper.loop(Looper.java:137)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.ActivityThread.main(ActivityThread.java:4441)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at java.lang.reflect.Method.invokeNative(Native Method)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at java.lang.reflect.Method.invoke(Method.java:511)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at dalvik.system.NativeStart.main(Native Method)
03-03 01:22:18.041: E/AndroidRuntime(27902): Caused by: java.lang.NullPointerException
03-03 01:22:18.041: E/AndroidRuntime(27902):    at com.example.slider.BaseActivity.onCreate(BaseActivity.java:35)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at com.example.slider.MainActivity.onCreate(MainActivity.java:12)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.Activity.performCreate(Activity.java:4465)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
03-03 01:22:18.041: E/AndroidRuntime(27902):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
03-03 01:22:18.041: E/AndroidRuntime(27902):    ... 11 more

Answer 1

The problem appears that the base class is not aware of the layout. Not sure how or why it worked for others without having to do something like this.. but I am new to Android.

I was getting the same error and solved by passing my layout to the base via onCreate.

So in the base, I modified onCreate to be like this:

protected void onCreate(Bundle savedInstanceState, int resLayoutID)
{
    super.onCreate(savedInstanceState);
    setContentView(resLayoutID);

Then, from my new activity, I have this:

@Override
protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState, R.layout.my_activity);

This code in my base now works instead of staying null:

drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerList = (ListView) findViewById(R.id.left_drawer);

btw, this result was suggested to me by a friend and it worked for me.

Answer 2

在main活动中，你必须在setContentView（）之后调用super.onCreate（savedInstanceState）

Answer 3

On the parent classBaseActivity :

• declare a protected abstract int getLayoutId();

• onCreate() I added the line

   setContentView(getLayoutId()); 

Now implement it on your subclass MainActivity something like:

 protected int getLayoutId() {
    return R.layout.activity_profile;
}

Please tell me if you know a better solution.

Answer 4

As suggested by oli, you need to call setContentView(R.layout.activity_view) in your main activity .

BaseActivity's onCreate must be called once content view in Main Activity has been set as shown below :

public class BaseActivity extends Activity {
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // REST Navigation drawer initialization
    }

}



public class MainActivity extends BaseActivity {

    protected void onCreate(Bundle savedInstanceState) {

        setContentView(R.layout.activity_view);
        super.onCreate(savedInstanceState);

        // REST APPLICATION CODE
    }
}

Answer 5

Your xml file should look something like this, taken from the android website: http://developer.android.com/training/implementing-navigation/nav-drawer.html

<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>

Answer 6

In you MainActivity just put set setContentView(R.layout.activity_main) before

super.onCreate(savedInstanceState);

like below:

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