java - 尝试在非活动类中调用方法时的 Java NPE
问题描述
我已经在这里和那里搜索了两天,但似乎没有解决方案不起作用。问题在Fitness.getSessionsClient(this, Objects.requireNonNull(GoogleSignIn.getLastSignedInAccount(2ndclass.mContext)))
于其传递的活动(this
)和上下文(2ndClass.mContext
)变量,我可以通过许多找到的方法填充(变量或非空或空通过调试器检查)。仍然 - 我总是得到 NPE (java.lang.NullPointerException) 或 getApplicationContext() 为空。有任何想法吗?
崩溃日志行:
E/<SOME TAG>: Error during PUT connection... Data: {"coord":{"lon":-0.13,"lat":51.51},"weather":[{"id":803,"main":"Clouds","description":"broken clouds","icon":"04d"}],"base":"stations","main":{"temp":13.11,"pressure":1033,"humidity":77,"temp_min":10,"temp_max":16.11},"visibility":10000,"wind":{"speed":3.1,"deg":330},"clouds":{"all":69},"dt":1568357213,"sys":{"type":1,"id":1414,"message":0.0113,"country":"GB","sunrise":1568352700,"sunset":1568398909},"timezone":3600,"id":2643743,"name":"London","cod":200} Message: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
代码片段:
第一(MainActivity)类:
public class 1stClass extends AppCompatActivity {
public static 1stClass instance;
public static Context mContext;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
instance = this;
mContext = getApplicationContext();
}
public final void 1stmethod(){
2ndClass.2ndmethod();
}
/**
* @return instance
*/
@Contract(pure = true)
public static 1stClass getInstance() { return instance; } // return.getInstance();
public static Context getContext() {
// return instance.getApplicationContext();
return mContext;
}
}
第二类:
public class 2ndClass extends 1stClass{
static 2ndClass instance;
public final void 2ndmethod() {
instance = this;
3rdClass MFP = new 3rdClass();
MFP.3rdmethod(..);
}
/**
* @return instance
*/
@Contract(pure = true)
public static 2ndClass getInstance() { return instance; } //return.getInstance();
}
非活动(第三)类:
public final class 3rdClass extends 2ndClass {
static 3rdClass instance;
public void 3rdmethod() {
instance = this;
Fitness.getSessionsClient(this, Objects.requireNonNull(GoogleSignIn.getLastSignedInAccount(2ndclass.mContext))) // <---- ERROR HERE
.insertSession(request)
.addOnSuccessListener(new OnSuccessListener<Void>() {
@Override
public void onSuccess(Void aVoid) {
Log.i(TAG, "Session insert was successful!");
}
})
.addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
Log.wtf(TAG, "There was a problem inserting the session: " +
e.getLocalizedMessage());
}
});
/**
* @return instance
*/
@Contract(pure = true)
public static MFPalInterface getInstance() {
return instance;
} // return.getInstance();
}
解决方案
我想我明白你在做什么,即使代码是一团糟。
2ndClass
您正在尝试在您的方法 '2ndmethod()'中创建自己的活动,然后在新创建的3rdClass
.
public final void 2ndmethod() {
3rdClass MFP = new 3rdClass();
MFP.3rdmethod(..);
}
即使您3rdClass
从Activity 扩展AppCompatActivity
,您也没有要求系统创建 Activity 实例并尝试自己创建它。这意味着新创建的实例没有上下文,系统也不知道它。
你需要做什么
通过调用startActivity()
当前运行的方法Activity
(在本例中我认为是 2ndClass)并传递一个意图来启动活动。像这样:
Intent intent = new Intent(this, 3rdClass.class); // this is your current Activity's reference.
currentActivity.startActivity(intent);
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