Question

我对讨论的话题有一些疑问。

我从以下代码中获取NullPointerException。我的问题是：

为什么我会收到NullPointerException？即为什么getActionBar（）返回null？

请求答案为Layman条款。

SettingActivity.java

public class SettingsActivity extends PreferenceActivity {
/**
 * Determines whether to always show the simplified settings UI, where
 * settings are presented in a single list. When false, settings are shown
 * as a master/detail two-pane view on tablets. When true, a single pane is
 * shown on tablets.
 */
private static final boolean ALWAYS_SIMPLE_PREFS = false;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setupActionBar();
}

/**
 * Set up the {@link android.app.ActionBar}, if the API is available.
 */
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        // Show the Up button in the action bar.
        getSupportActionBar()
        getActionBar().setDisplayHomeAsUpEnabled(true);
    }
}

Style.xml

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
</style>

的build.gradle

dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
compile 'com.android.support:appcompat-v7:22.1.1'
compile 'com.android.support:support-v4:22.1.1'
}

错误

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at com.example.deep.sunshine.SettingsActivity.setupActionBar(SettingsActivity.java:59)
at com.example.deep.sunshine.SettingsActivity.onCreate(SettingsActivity.java:49)

PreferenceActivity - ＆gt; getActionBar（）。setDisplayHomeAsUpEnabled给出NullPointerException

0 个答案: