这是我发现的有关使用context
:
1)。在Activity
自身内部,this
用于放大布局和菜单,注册上下文菜单,实例化窗口小部件,启动其他活动,在中创建新Intent
内容Activity
,实例化首选项或可用的其他方法Activity
。
充气布局:
View mView = this.getLayoutInflater().inflate(R.layout.myLayout, myViewGroup);
充气菜单:
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
this.getMenuInflater().inflate(R.menu.mymenu, menu);
return true;
}
注册上下文菜单:
this.registerForContextMenu(myView);
实例化小部件:
TextView myTextView = (TextView) this.findViewById(R.id.myTextView);
开始一个Activity
:
Intent mIntent = new Intent(this, MyActivity.class);
this.startActivity(mIntent);
实例化首选项:
SharedPreferences mSharedPreferences = this.getPreferenceManager().getSharedPreferences();
2)。对于应用程序范围的类,getApplicationContext()
在应用程序的生命周期中使用此上下文作为上下文。
检索当前Android软件包的名称:
public class MyApplication extends Application {
public static String getPackageName() {
String packageName = null;
try {
PackageInfo mPackageInfo = getApplicationContext().getPackageManager().getPackageInfo(getApplicationContext().getPackageName(), 0);
packageName = mPackageInfo.packageName;
} catch (NameNotFoundException e) {
// Log error here.
}
return packageName;
}
}
绑定应用程序范围的类:
Intent mIntent = new Intent(this, MyPersistent.class);
MyServiceConnection mServiceConnection = new MyServiceConnection();
if (mServiceConnection != null) {
getApplicationContext().bindService(mIntent, mServiceConnection, Context.BIND_AUTO_CREATE);
}
3)。对于侦听器和其他类型的Android类(例如ContentObserver),请使用Context替换,例如:
mContext = this; // Example 1
mContext = context; // Example 2
其中this
或者context
是一个类(活动等)的情况下。
Activity
上下文替换:
public class MyActivity extends Activity {
private Context mContext;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mContext = this;
}
}
侦听器上下文替换:
public class MyLocationListener implements LocationListener {
private Context mContext;
public MyLocationListener(Context context) {
mContext = context;
}
}
ContentObserver
上下文替换:
public class MyContentObserver extends ContentObserver {
private Context mContext;
public MyContentObserver(Handler handler, Context context) {
super(handler);
mContext = context;
}
}
4)。对于BroadcastReceiver
(包括嵌入式/嵌入式接收器),请使用接收器自身的上下文。
外部BroadcastReceiver
:
public class MyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (action.equals(Intent.ACTION_SCREEN_OFF)) {
sendReceiverAction(context, true);
}
private static void sendReceiverAction(Context context, boolean state) {
Intent mIntent = new Intent(context.getClass().getName() + "." + context.getString(R.string.receiver_action));
mIntent.putExtra("extra", state);
context.sendBroadcast(mIntent, null);
}
}
}
内联/嵌入BroadcastReceiver
:
public class MyActivity extends Activity {
private BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final boolean connected = intent.getBooleanExtra(context.getString(R.string.connected), false);
if (connected) {
// Do something.
}
}
};
}
5)。对于服务,请使用服务自己的上下文。
public class MyService extends Service {
private BroadcastReceiver mBroadcastReceiver;
@Override
public void onCreate() {
super.onCreate();
registerReceiver();
}
private void registerReceiver() {
IntentFilter mIntentFilter = new IntentFilter();
mIntentFilter.addAction(Intent.ACTION_SCREEN_OFF);
this.mBroadcastReceiver = new MyBroadcastReceiver();
this.registerReceiver(this.mBroadcastReceiver, mIntentFilter);
}
}
6)。对于Toast,通常使用getApplicationContext()
,但在可能的情况下,请使用从Activity,Service等传递的上下文。
使用应用程序的上下文:
Toast mToast = Toast.makeText(getApplicationContext(), message, Toast.LENGTH_LONG);
mToast.show();
使用从源传递的上下文:
public static void showLongToast(Context context, String message) {
if (context != null && message != null) {
Toast mToast = Toast.makeText(context, message, Toast.LENGTH_LONG);
mToast.show();
}
}
最后,请勿getBaseContext()
按照Android框架开发人员的建议使用。
更新:添加Context
用法示例。