我正在创建一个Android应用程序,并希望在Application类中存储一个变量。该变量表示哪个活动当前处于焦点状态。应用程序类空指针异常
我的目标是在onResume()
中设置这个变量并将其重置为onPause()
。这两种方法都被称为应用程序初始化。每当我运行我的代码时,该软件就会在空指针溢出的基础上崩溃,并尝试修改Application类中的变量。据我所知,即使我已经测试了代码并知道它称为应用程序类'onCreate()
,但在我看来,应用程序类似于null
。
我正确地认为它连接到应用程序类未完全创建?或者它与我的所有实例有关?我对Android非常陌生,以前没有处理过Application类 - 就我所知,我已经正确地遵循了指南和教程。我希望这是一个简单的错误。
任何和所有的建议非常感谢!
MainActivity.java
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
//[... other initialisations...]
// Tells software what window is in focus.
// Reference to Application class
private MyApplicationClass app = (MyApplicationClass)getApplication();
private static final int outOfFocus = 0;
private static final int inFocus = 1;
@Override
protected void onResume() {
super.onResume();
//[... other code...]
app.setActivityFocusIndicator(inFocus); //Crashes here
}
@Override
protected void onPause() {
super.onPause();
//[... other code...]
app.setActivityFocusIndicator(outOfFocus); //Crashes here
}
}
MyApplicationClass.java
public class MyApplicationClass extends Application {
private int activityFocusIndicator;
/* activityFocusIndicator is here to indicate which activity is in focus.
* 0 = Nothing in focus (written when pausing.)
* 1 = MainActivity
* 2 = ...
* ...
*/
public void setActivityFocusIndicator(int activityFocusIndicator) {
this.activityFocusIndicator = activityFocusIndicator;
}
public int getActivityFocusIndicator() {
return activityFocusIndicator;
}
@Override
public void onCreate() {
super.onCreate();
Log.d("App", "App was created."); // This line is reached.
}
}
清单文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.someApp"
android:versionCode="1"
android:versionName="1.0" >
<uses-feature android:name="android.hardware.bluetooth_le"
android:required="true"/>
<uses-sdk
android:minSdkVersion="18"
android:targetSdkVersion="19" />
<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/TabTheme"
android:name="com.example.someName.MyApplicationClass" >
<activity
android:name="com.example.someName.MainActivity"
android:label="@string/app_name"
android:screenOrientation="portrait"
android:launchMode="singleInstance" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
...
</activity>
<!-- ... [other activities declared]... -->
<service
android:name=".BluetoothService"/>
</application>
</manifest>
如果问我可以张贴logcat的。
合理的逻辑,这正是问题是,谢谢!这是我将来在使用该课程时需要注意的事项。 – clb9355 2014-11-22 04:47:10