在显示java.lang.NullPointerException ANDROID android.content.ContextWrapper.getPackageName [英] java.lang.NullPointerException at android.content.ContextWrapper.getPackageName ANDROID

问题描述

嘿，我想从我的MainActivity但不是在onCreate方法开始一个活动。

Hey I want to start an Activity from my MainActivity but not in the oncreate method.

public void awe()
{
    Intent myIntent = new Intent(MainActivity.this, Awesome.class);
    MainActivity.this.startActivity(myIntent);
}

另一类调用方法敬畏（）和我得到的是一个崩溃以及

Another class calls the method awe() and what I get is a crash and

05-25 04:06:51.034: E/AndroidRuntime(7161): FATAL EXCEPTION: main
05-25 04:06:51.034: E/AndroidRuntime(7161): java.lang.NullPointerException
05-25 04:06:51.034: E/AndroidRuntime(7161):     at android.content.ContextWrapper.getPackageName(ContextWrapper.java:151)
05-25 04:06:51.034: E/AndroidRuntime(7161):     at android.content.ComponentName.<init>(ComponentName.java:106)
05-25 04:06:51.034: E/AndroidRuntime(7161):     at android.content.Intent.<init>(Intent.java:2895)
05-25 04:06:51.034: E/AndroidRuntime(7161):     at package name.MainActivity.awe(MainActivity.java:215)

有人知道我能做些什么？

Someone knows what I can do?

MainActivity

MainActivity

public class MainActivity extends Activity implements OnClickListener { 
// (variable stuff)
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

          buttonE = (Button) findViewById(R.id.buttonEASY); 
          buttonM = (Button) findViewById(R.id.buttonMED);

// here I do all that button stuff for the layout
}



    public void onClick(View arg0) {
        System.out.println("click");
        if (arg0==buttonE)  {

                 int checkedRadioButton = radioGroup1.getCheckedRadioButtonId();
                                 String radioButtonSelected = "";

                                 switch (checkedRadioButton) {

                                  case R.id.radio0 : radioButtonSelected = "radiobutton1";
                                  Toast.makeText(getApplicationContext(), "Easy, 10 selected", Toast.LENGTH_SHORT).show();
                                  setContentView(R.layout.raten);

// Button stuff, again.


}



public void awe()
{   Intent tutorial = new Intent(MainActivity.this, Awesome.class); 
    if (tutorial != null) { startActivity(tutorial); } 

}

Easy.java

Easy.java

没什么这里，在这里我指的是敬畏的地方（）：

Nothing important here, the place where I refer to awe():

if (s==max+1){System.out.println("AWESOME!"); MainActivity mA = new MainActivity(); mA.awe();}

Awesome.java

Awesome.java

public class Awesome extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.awesome);
    }

我希望我现在贴的一切，是非常重要的。

I hope I now posted everything that is important

推荐答案

需要考虑的事情与Android活动：

Things to consider with Android Activities:

你有你的类，延长活动中定义的的Andr​​oidManifest.xml

Do you have your classes that extend Activity defined in the AndroidManifest.xml?

您知道您的上下文使用时 意图

有关呼叫意图，总是检查空，如果你是通过软件包名美其名曰：

For calling intents, always check for null, if you are calling via packagename:

Intent mTutorial = new Intent(MainActivity.this, TutorialActivity.class); 

this.startActivity(mTutorial); 

您的问题无非是想打电话给你的敬畏（）方法是在没有你的MainActivity正确的上下文中的另一个活动：的 http://developer.android.com/reference/android/content/Intent.html 。

Your problem was simply trying to call your "awe()" method was in another Activity that did not have the correct Context for your MainActivity: http://developer.android.com/reference/android/content/Intent.html.

Android的意图需要一个背景和类。

Android Intent requires a "Context" and a "Class".

更新：这里是另一篇文章，这将有助于：

<一个href=\"http://stackoverflow.com/questions/3872063/android-launch-an-application-from-another-application/15465797#15465797\">Android从另一个应用程序启动应用程序

问候，

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