Question

我可以在android ??

中的setContentView(R.layout.activity_main);之前以编程方式初始化ImageView或任何其他视图

实际上我得到的是自定义类的实例（不是活动）在onCreate方法之前全局像这样

MyInAppPurchaseBilling myInAppPurchaseBilling = new MyInAppPurchaseBilling(MenuClass.this);

并且在该类构造函数中我必须使用该上下文来初始化我的首选项类

public MyInAppPurchaseBilling(Activity launcher) {
        this.activity = launcher;
        tinyDB= new TinyDB(launcher);
    }

这是我面临的错误logcat

07-05 17:22:01.852 9660-9660/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.write.urdu.poetry.urdutexteditor, PID: 9660
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.write.urdu.poetry.urdutexteditor/com.write.urdu.poetry.urdutexteditor.MenuClass}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
    at android.app.ActivityThread.access$900(ActivityThread.java:157)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:5551)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
    at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
    at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:375)
    at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:370)
    at com.write.urdu.poetry.urdutexteditor.TinyDB.<init>(TinyDB.java:55)
    at com.write.urdu.poetry.urdutexteditor.inapppurchase.MyInAppPurchaseBilling.<init>(MyInAppPurchaseBilling.java:48)
    at com.write.urdu.poetry.urdutexteditor.MenuClass.<init>(MenuClass.java:38)
    at java.lang.Class.newInstance(Native Method)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2329)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494) 
    at android.app.ActivityThread.access$900(ActivityThread.java:157) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:148) 
    at android.app.ActivityThread.main(ActivityThread.java:5551) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)

Answer 1

在执行MenuClass.this对象的构造函数时是否创建了MyInAppPurchaseBilling对象？在这种情况下（可能直到在MenuClass.this上调用onCreate()，但我不确定这一点）Activity对象内部的上下文（在这种情况下表示MenuClass.this）尚未设置。

Answer 2

你要做的是

#include <QApplication>

#include <QDialog>
#include <QVBoxLayout>
#include <QLabel>
int main(int argc, char *argv[])
{

    QApplication app(argc, argv);

    QDialog *_waitQD = new QDialog;
    QVBoxLayout *_waitQVBL = new QVBoxLayout;
    QLabel *_waitQL = new QLabel("Loading...");

    _waitQD->setMinimumSize(QSize(95,35));
    _waitQVBL->addWidget(_waitQL);
    _waitQD->setLayout(_waitQVBL);

    _waitQD->show();

    return app.exec();
}

Answer 3

试试这个：

View view = View.inflate(this, R.layout.activity_main, null); // view Exists after this code
TextView t = (TextView) view.findViewById(R.id.text);
setContentView(view);
t.setText("something");

在这里，您可以看到在findViewById()之前调用setContentView()。但是视图存在是因为它被夸大了但它可能对你有帮助。

Answer 4

这是我的MenuClass Activity代码我在setContentView（）之前在MenuClass onCreate（）方法中初始化TinyDB，并在从偏好类中获取保存的布尔值后完成我的工作

public class MenuClass extends Activity {

TinyDB tinyDB;    
    MyInAppPurchaseBilling myInAppPurchaseBilling = new MyInAppPurchaseBilling(MenuClass.this);

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

    tinyDB= new TinyDB(MenuClass.this);
        if (!tinyDB.getBoolean(Constant.isAdsDisabled)) {
//do your work
        }
        setContentView(R.layout.activity_menu_class);
   }
}

这是我的MyInAppPurchaseBilling类的代码我在其构造函数中什么也没做，但创建了onCreate的单独方法，就像activity的onCreate一样，并在其中初始化TinyDB，并在超级后调用MenuClass onCreate中此类的onCreate方法。*** line ...这样我成功地在MyInAppPurchaseBilling类中初始化TinyDB，将boolean值放在app的开头，然后在Menuclass中获取该布尔值以进一步处理

      public class MyInAppPurchaseBilling {

            private TinyDB tinyDB;    
            Activity activity;

            public MyInAppPurchaseBilling(Activity launcher) {
                this.activity = launcher;
            }

            public void onCreate() {
                tinyDB= new TinyDB(activity);
    }
}

我可以在setcontentview android

4 个答案: