Question

我是Android开发的新手。我的项目中有两个Java文件。一个文件包含我的主要活动，因此我想将数据从一个Java文件传输到另一个包含主要活动的文件。

cordovaExample.java：

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

import org.apache.cordova.*;
public class cordovaExample extends DroidGap
{
@Override
 public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    super.loadUrl("file:///android_asset/www/index.html");

    Bundle extras = getIntent().getExtras();
    String phno = extras.getString("novel.PhoneNumber");
   Toast.makeText(getApplicationContext(),phno,Toast.LENGTH_LONG).show();



}
}

novel.java

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

public class novel extends Activity
{ 
public String PhoneNumber;
Context mcontext;
public String getNumber()
{



 TelephonyManager tMgr=(TelephonyManager)mcontext.getSystemService(Context.TELEPHONY_SERVICE); 

         Intent intent = new Intent(this, cordovaExample.class);
            intent.putExtra("novel.PhoneNumber", PhoneNumber);
                startActivity(intent);
               return PhoneNumber = tMgr.getLine1Number();
        }

}

所以我想将"PhoneNumber"从novel.java转移到cordovaExample.java，但在novel.java中，运行应用程序后，我在模拟器中获得"unfortunately app has stopped"。< / p>

这是logcat

08-12 15:49:37.657: E/AndroidRuntime(779): FATAL EXCEPTION: main
08-12 15:49:37.657: E/AndroidRuntime(779): java.lang.RuntimeException: Unable to start activity  ComponentInfo{org.apache.cordova.example/org.apache.cordova.example.cordovaExample}: java.lang.NullPointerException
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.access$600(ActivityThread.java:123)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.os.Looper.loop(Looper.java:137)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.main(ActivityThread.java:4424)
08-12 15:49:37.657: E/AndroidRuntime(779):  at java.lang.reflect.Method.invokeNative(Native Method)
08-12 15:49:37.657: E/AndroidRuntime(779):  at java.lang.reflect.Method.invoke(Method.java:511)
08-12 15:49:37.657: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-12 15:49:37.657: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-12 15:49:37.657: E/AndroidRuntime(779):  at dalvik.system.NativeStart.main(Native Method)
08-12 15:49:37.657: E/AndroidRuntime(779): Caused by: java.lang.NullPointerException
08-12 15:49:37.657: E/AndroidRuntime(779):  at org.apache.cordova.example.cordovaExample.onCreate(cordovaExample.java:20)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.Activity.performCreate(Activity.java:4465)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
08-12 15:49:37.657: E/AndroidRuntime(779):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
08-12 15:49:37.657: E/AndroidRuntime(779):  ... 11 more

另外，如果我尝试简单程序，我会得到相同的结果：

cordovaExample.java

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

import org.apache.cordova.*;
public class cordovaExample extends DroidGap
{
@Override
 public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    super.loadUrl("file:///android_asset/www/index.html");

   novel c=new novel()
   int a=c.getNumber();
   Toast.makeText(getApplicationContext(),a,Toast.LENGTH_LONG).show();



}
}

novel.java

package org.apache.cordova.example;

import android.content.Context;
import android.content.Intent;
import android.telephony.*;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Toast;

public class novel extends Activity
{ 
public int a=0;
public int getNumber()
{

    a=5;

 return a;
        }

}

我该如何解决这个问题？

Answer 1

您在返回块后使用了intent语句

return PhoneNumber = tMgr.getLine1Number（）;

Intent myIntent = new Intent（novel.this，cordovaExample.class）;

返回阻止后，任何代码都显示无法访问的错误。

传递intent参数后，您可以调用return。

   TelephonyManager tMgr=(TelephonyManager)mcontext.getSystemService(Context.TELEPHONY_SERVICE); 

   Intent intent = new Intent(this, cordovaExample.class);
   intent.putExtra("novel.PhoneNumber", PhoneNumber);
   startActivity(intent);
   return PhoneNumber = tMgr.getLine1Number();

Answer 2

Android API指南包含有关how to pass data between between Activities/Services within a single application的最终常见问题解答项目。

试试这个，

在小说中这样设置电话号码

Intent myIntent = new Intent(novel.this, cordovaExample.class);
myIntent.putExtra("phone", 989898989);
startActivity(myIntent);

在cordovaExample文件中

执行以下操作以获取phoneNumber

Bundle b = this.getIntent().getExtras();
String i = b.getString("phone");

如果您无法传递数据，则替代方法是声明公共方法并传递它们，请参阅以下示例，

novel.java

private static String phoneNumber = "";

public void onCreate()
{
    ...
    phoneNumber = "9898989898";
    ...
}

public static String getPhoneNumber()
{
      return phoneNumber;
}

cordovaExample.java

private static String phoneNumber = ""; 

phoneNumber = novel.getPhoneNumber();

Answer 3

将您的代码更改为：您在cordovaExample.java中获得了NPE，因为在novel中您将null电话号码放入了额外内容。

     TelephonyManager tMgr=(TelephonyManager)mcontext.getSystemService(Context.TELEPHONY_SERVICE); 

             Intent intent = new Intent(this, cordovaExample.class);
             PhoneNumber = tMgr.getLine1Number(); // Check PhoneNumber  not null here before send to cordovaExample
if (PhoneNumber !=null ){
                intent.putExtra("novel.PhoneNumber", PhoneNumber);
                    startActivity(intent);}

            }

在Android中将数据从一个Java文件传递到另一个Java文件

3 个答案: