如何调用方法时,我解决NullPointerException异常? [英] How do i resolve NullPointerException when calling methods?
问题描述
我是一个菜鸟到Android和我有打电话从其他类中的方法的问题。该方法效果优良工程从自己的类中调用的时候,但我得到一个NullPointerException异常,当我从另一个类调用它。任何帮助将大大AP preciated。这里是我的code;
从Class2中调用方法class1的:
BottlesActivity研究所=新BottlesActivity();
inst.call0();
在1类方法:
公共无效call0(){
尝试{
意图callIntent =新意图(Intent.ACTION_CALL);
callIntent.setData(Uri.parse(电话:1234567890/ * + * phonenumber0 /));
startActivity(callIntent); //< - 这行导致NullPointerException异常
}赶上(ActivityNotFoundException activityException){
Log.e(拨号-榜样,呼叫失败,activityException);
}
}
下面是我的logcat
20 09-06:51:33.237:E / AndroidRuntime(18192):显示java.lang.NullPointerException
09-06 20:51:33.237:E / AndroidRuntime(18192):在android.app.Activity.startActivityForResult(Activity.java:2893)
09-06 20:51:33.237:E / AndroidRuntime(18192):在android.app.Activity.startActivity(Activity.java:3003)
09-06 20:51:33.237:E / AndroidRuntime(18192):在com.bryanjrichardson.GSCC.BottlesActivity.call0(GoldandSilverCoinCalculatorActivity.java:857)
09-06 20:51:33.237:E / AndroidRuntime(18192):在com.bryanjrichardson.GSCC.SimpleItemizedOverlay $ 1.onClick(SimpleItemizedOverlay.java:204)
09-06 20:51:33.237:E / AndroidRuntime(18192):在com.android.internal.app.AlertController $ ButtonHandler.handleMessage(AlertController.java:174)
09-06 20:51:33.237:E / AndroidRuntime(18192):在android.os.Handler.dispatchMessage(Handler.java:99)
09-06 20:51:33.237:E / AndroidRuntime(18192):在android.os.Looper.loop(Looper.java:130)
09-06 20:51:33.237:E / AndroidRuntime(18192):在android.app.ActivityThread.main(ActivityThread.java:3859)
09-06 20:51:33.237:E / AndroidRuntime(18192):在java.lang.reflect.Method.invokeNative(本机方法)
09-06 20:51:33.237:E / AndroidRuntime(18192):在java.lang.reflect.Method.invoke(Method.java:507)
09-06 20:51:33.237:E / AndroidRuntime(18192):在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:839)
09-06 20:51:33.237:E / AndroidRuntime(18192):在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
09-06 20:51:33.237:E / AndroidRuntime(18192):在dalvik.system.NativeStart.main(本机方法)
如果您的2类 2分开活动,你的情况会导致空指针异常,因为当第2个活动正在运行,第一个活动停止(终止) - >这是Android操作系统的机制,不能更改
对于你的情况的解决方案:
-
(1)活动1是别人的父母,这种情况下是适用于应用类或TabHost(复杂)。
-
(2)创建像静态方法的 @ Zapl的答案;但它仍然不是相当不错的,因为这种静态的方法应该是在共同使用,而不是里面的1级 - >修改:创建像下面的一个共同的类别:
这是工具类:
公共类GlobalUtil
{
公共静态无效startUrlActivity(上下文的背景下,字符串URL){
尝试{
意图callIntent =新意图(Intent.ACTION_CALL);
callIntent.setData(Uri.parse(URL));
context.startActivity(callIntent); //< - 通过当前活动或上下文
}赶上(ActivityNotFoundException activityException){
Log.e(拨号-榜样,呼叫失败,activityException);
}
}
}
和任何其他活动类中可以称之为:
GlobalUtil.startUrlActivity(这一点,电话:1234567890/ * + * phonenumber0 /);
或
GlobalUtil.startUrlActivity(getBaseContext()getApplicationContext(),YOUR_URL);
I'm a noob to android and i am having an issue calling a method from another class. The method works works fine when called from within its own class, but i get a nullpointerexception when i call it from another class. Any help would be greatly appreciated. Here is my code;
Calling method in class1 from class2:
BottlesActivity inst = new BottlesActivity();
inst.call0();
Method in class 1:
public void call0() {
try {
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setData(Uri.parse("tel:1234567890"/*+phonenumber0*/));
startActivity(callIntent); //<--This line causes nullpointerexception
} catch (ActivityNotFoundException activityException) {
Log.e("dialing-example", "Call failed", activityException);
}
}
Here is my Logcat
09-06 20:51:33.237: E/AndroidRuntime(18192): java.lang.NullPointerException
09-06 20:51:33.237: E/AndroidRuntime(18192): at android.app.Activity.startActivityForResult(Activity.java:2893)
09-06 20:51:33.237: E/AndroidRuntime(18192): at android.app.Activity.startActivity(Activity.java:3003)
09-06 20:51:33.237: E/AndroidRuntime(18192): at com.bryanjrichardson.GSCC.BottlesActivity.call0(GoldandSilverCoinCalculatorActivity.java:857)
09-06 20:51:33.237: E/AndroidRuntime(18192): at com.bryanjrichardson.GSCC.SimpleItemizedOverlay$1.onClick(SimpleItemizedOverlay.java:204)
09-06 20:51:33.237: E/AndroidRuntime(18192): at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:174)
09-06 20:51:33.237: E/AndroidRuntime(18192): at android.os.Handler.dispatchMessage(Handler.java:99)
09-06 20:51:33.237: E/AndroidRuntime(18192): at android.os.Looper.loop(Looper.java:130)
09-06 20:51:33.237: E/AndroidRuntime(18192): at android.app.ActivityThread.main(ActivityThread.java:3859)
09-06 20:51:33.237: E/AndroidRuntime(18192): at java.lang.reflect.Method.invokeNative(Native Method)
09-06 20:51:33.237: E/AndroidRuntime(18192): at java.lang.reflect.Method.invoke(Method.java:507)
09-06 20:51:33.237: E/AndroidRuntime(18192): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
09-06 20:51:33.237: E/AndroidRuntime(18192): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
09-06 20:51:33.237: E/AndroidRuntime(18192): at dalvik.system.NativeStart.main(Native Method)
If your 2 classes are 2 separated Activities, your case will cause Null Pointer Exception, because when 2nd activity is running, 1st activity is stopped (terminated) -> this is Android OS mechanism, you can not change.
Solutions for your case:
(1) Activity 1 is parent of others, this case is suitable for Application class or TabHost (complicated).
(2) Create static method like @Zapl's answer; But it's still not quite nice because this static method should be in common use instead of inside Class 1 -> modify: Create a common Class like following:
This is utility class:
public class GlobalUtil
{
public static void startUrlActivity(Context context, String url) {
try {
Intent callIntent = new Intent(Intent.ACTION_CALL);
callIntent.setData(Uri.parse(url));
context.startActivity(callIntent); //<-- pass current activity or context
} catch (ActivityNotFoundException activityException) {
Log.e("dialing-example", "Call failed", activityException);
}
}
}
And inside any other activity class you can call it:
GlobalUtil.startUrlActivity(this, "tel:1234567890"/*+phonenumber0*/");
OR
GlobalUtil.startUrlActivity(getBaseContext().getApplicationContext(), "your_url");
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