getContext() returns Null

Question

我在Android中使用getContext((方法来获取上下文，然后创建文件。但是，当从崩溃中调用应用程序，然后访问getContext((时，我总是会得到一个空指针异常。

下面是我在崩溃后调用的代码。此代码在崩溃前运行良好，但在崩溃后失败。

synchronized public void insertR(String filename,String content) {
// TODO Auto-generated method stub
String filename = filename;
String string = content;
Context context = MyActivity.getAppContext();
FileOutputStream outputStream;
try {//Context.MODE_PRIVATE
Log.v("insertR", content);
System.out.println(filename);
System.out.println(context); //prints null
outputStream = context.openFileOutput(filename, Context.MODE_PRIVATE);
outputStream.write(string.getBytes());
outputStream.flush();
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
} }
public class MyActivity extends Activity {
public static Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple_dynamo);
context = getApplicationContext();
TextView tv = (TextView) findViewById(R.id.textView1);
tv.setMovementMethod(new ScrollingMovementMethod());
}
public static Context getAppContext() {
try {
return context;
} catch (Exception e) {
return MyActivity.getAppContext();
}
}}

Answer 1

像这样更改insertR()方法：

synchronized public void insertR(Context context, String filename,String content) {
// TODO Auto-generated method stub
String filename = filename;
String string = content;
FileOutputStream outputStream;
try {//Context.MODE_PRIVATE
Log.v("insertR", content);
System.out.println(filename);
System.out.println(context); //prints null
outputStream = context.openFileOutput(filename, Context.MODE_PRIVATE);
outputStream.write(string.getBytes());
outputStream.flush();
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
} 
}

如果您想从MainActivity调用它，请这样做：

insertR(this, fileName, content);

或

insertR(getApplicationContext(), fileName, content);

Answer 2

我相信，既然您在一个活动中，就可以使用静态函数getApplicationContext()来检索上下文。