Question

我要在导航抽屉中添加阴影。这是我使用的代码。

创建了一个navbar_shadow.xml并将其添加到drawable中。这是代码。

<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<gradient android:startColor="#111"
    android:endColor="#00000000">
</gradient>
<size
    android:height="@dimen/activity_vertical_margin"
    android:width="5dp">
</size>

然后将以下代码添加到NavigationDrawer.java

mDrawerLayout.setDrawerShadow(R.drawable.navbar_shadow, GravityCompat.START);

所以，当我运行此代码时。它开始崩溃并跟随错误显示。这是我得到的Logcat。

11-27 09:43:47.787    6541-6541/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.myayubo, PID: 6541
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myayubo/com.myayubo.Extract}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2338)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
            at android.os.Handler.dispatchMessage(Handler.java:110)
            at android.os.Looper.loop(Looper.java:193)
            at android.app.ActivityThread.main(ActivityThread.java:5299)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.myayubo.Extract.onCreate(Extract.java:63)
            at android.app.Activity.performCreate(Activity.java:5264)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
            at android.os.Handler.dispatchMessage(Handler.java:110)
            at android.os.Looper.loop(Looper.java:193)
            at android.app.ActivityThread.main(ActivityThread.java:5299)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
            at dalvik.system.NativeStart.main(Native Method)

请帮我成功添加我的影子。感谢。

Answer 1

确保您使用mDrawerLayout

初始化了findViewById

编辑1： 更改订单

首先使用findViewById初始化布局，然后将drawable添加到布局

Answer 2

你应该使用findViewById

初始化mDrawerLayout

首先findViewById然后将drawable添加到布局

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

    mDrawerLayout.setDrawerShadow(R.drawable.navbar_shadow, GravityCompat.START);

    mTitle = mDrawerTitle = getTitle();
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerLayout.setDrawerShadow(R.drawable.navbar_shadow, Gravity.LEFT);/// it should be here after findviewbyid
    mLenear = (ScrollView)findViewById(R.id.leftDrawer);

Answer 3

您对setDrawerShadow的调用需要在findViewById

之后

即

    mTitle = mDrawerTitle = getTitle();
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerLayout.setDrawerShadow(R.drawable.navbar_shadow, GravityCompat.START);

目前，您正在尝试在找到视图之前应用阴影，因此是空指针。

为Navigaton Drawer添加阴影会出错

3 个答案: