如何在onCreate方法中从另一个类调用方法？

问题描述

Java：在android SDK中，如何在onCreate()方法中从另一个类调用方法？

logcat的：

08-28 22:27:24.152: W/dalvikvm(13642): threadid=1: thread exiting with uncaught exception (group=0x40015578)
08-28 22:27:24.156: E/AndroidRuntime(13642): FATAL EXCEPTION: main
08-28 22:27:24.156: E/AndroidRuntime(13642): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.valgriz.high.low/com.valgriz.high.low.Game}: java.lang.NullPointerException
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.os.Handler.dispatchMessage(Handler.java:99)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.os.Looper.loop(Looper.java:130)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.ActivityThread.main(ActivityThread.java:3687)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at java.lang.reflect.Method.invokeNative(Native Method)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at java.lang.reflect.Method.invoke(Method.java:507)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at dalvik.system.NativeStart.main(Native Method)
08-28 22:27:24.156: E/AndroidRuntime(13642): Caused by: java.lang.NullPointerException
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.Activity.findViewById(Activity.java:1647)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at com.valgriz.high.low.Package.runThis(Package.java:16)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at com.valgriz.high.low.Game.onCreate(Game.java:34)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
08-28 22:27:24.156: E/AndroidRuntime(13642):    ... 11 more

像这样：

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main );

    MyClass work = new MyClass();
    work.doSomething();

}

public class MyClass{

    public void doSomething(){
        Log.d("tag", "yes sir!");
    }
}

您需要声明和实例化该类对象，或者根据它是否是静态的来调用它。

private NonStaticObject dynamicObject;
private StaticObject stObject;


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

    //instantiate the non static object
    dynamicObject = new NonStaticObject();
    dynamicObject.method();

    //or simply call the static method.
    stObject.method();

}

从日志（下面的代码段）中，您似乎正在尝试使用错误的ID查找视图， 或者不存在/未实例化/创建/创建的视图已被删除。

08-28 22:27:24.156: E/AndroidRuntime(13642): Caused by: java.lang.NullPointerException
08-28 22:27:24.156: E/AndroidRuntime(13642):    at android.app.Activity.findViewById(Activity.java:1647)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at com.valgriz.high.low.Package.runThis(Package.java:16)
08-28 22:27:24.156: E/AndroidRuntime(13642):    at com.valgriz.high.low.Game.onCreate(Game.java:34)

请检查您要查找的视图是否已完成创建，并且您使用正确的ID引用该视图。

另外，根据onCreate(Bundle)的android文档（以下 onCreate(Bundle)应满足以下条件。 请检查您是否正在使用super.onCreate(savedInstanceState);与父对象进行呼叫super.onCreate(savedInstanceState); 从Game类的onCreate(Bundle)方法的第一行开始。

派生类必须调用此方法的超类的实现。 如果不这样做，将引发异常。

您可以这样做：

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

    // call method from other class
    myclass Objectc = new myclass();
    Objectc.methodA();
}