java - Android app force closes while going on another activity

Question

I am making an android app using android 2.2 and eclipse.

There are two workflows of the app:

WF1: CoverPageApp -> LoginActivity -> Dashboard.

WF2: CoverPageApp -> RegisterActivity -> Dashboard.

But as I click on the Start Button in CoverPageApp to go on another activity, i.e LoginActivity, the app force closes. I have also included the LogCat which shows error of Null Exception and in the LoginActivity Java File it points on the line 51: btnLinkToRegistrScrn = (Button) findViewById(R.id.LinkToRegisterScreen);

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.app.android"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:targetSdkVersion="15" android:minSdkVersion="8" />

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >

        <activity
            android:enabled="true"
            android:name=".PageApp"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity 
            android:enabled="true"
            android:name=".LoginActivity1"
            android:label="Login Activity" >
        </activity>

        <activity
            android:enabled="true"
            android:name=".CAActivity"
            android:label="Register Activity" >
        </activity>

        <activity
            android:enabled="true"
            android:name=".DashboardActivity"
            android:label="Dashboard Activity" >
        </activity>

    </application>

  </manifest>

PageApp.java

import android.app.Activity;
import android.os.Bundle;
//import android.content.Context;
import android.content.Intent;
import android.widget.Button;
import android.view.View;

public class PageApp extends Activity {

    Button startbutton;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.coverpage);
        addListenerOnButton();
   }


    public void addListenerOnButton() {

        //final Context context1 = this;

        startbutton = (Button) findViewById(R.id.button1);

        startbutton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                Intent intent1 = new Intent(arg0.getContext(), LoginActivity1.class); 
            //    intent1.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(intent1); 
                finish();
                }
            });

    }

}

Log.java

import android.app.Activity;
//import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
//import android.view.View.OnClickListener;
import android.widget.Button;
//import android.widget.TextView;


public class Log extends Activity {

    Button btnLinkToRegistrScrn;
    Button loginbtn1;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
     setContentView(R.layout.login);
     addListenerOnButton();
//     btnLinkToRegistrScrn = (Button) findViewById(R.id.LinkToRegisterScreen); 

   }


    public void addListenerOnButton() {

        //final Context context2 = this;

            loginbtn1 = (Button) findViewById(R.id.btnLogin);

            loginbtn1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {

                Intent intent = new Intent(arg0.getContext(), DashboardActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                         startActivity(intent);   
            }

        });
    }


    { 
        // Link to Register Screen 
        btnLinkToRegistrScrn = (Button) findViewById(R.id.LinkToRegisterScreen); 
        btnLinkToRegistrScrn.setOnClickListener(new View.OnClickListener() { 
           @Override
            public void onClick(View v) { 
                Intent i = new Intent(v.getContext(), CAaactivity.class); 
              //  i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(i);
                } 
       }); 

    }   

   }

LOGCAT

05-31 17:53:19.691: D/AndroidRuntime(1958): Shutting down VM
05-31 17:53:19.710: W/dalvikvm(1958): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
05-31 17:53:19.730: E/AndroidRuntime(1958): FATAL EXCEPTION: main
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.os.Looper.loop(Looper.java:123)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.ActivityThread.main(ActivityThread.java:4627)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at java.lang.reflect.Method.invokeNative(Native Method)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at java.lang.reflect.Method.invoke(Method.java:521)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at dalvik.system.NativeStart.main(Native Method)
05-31 17:53:19.730: E/AndroidRuntime(1958): Caused by: java.lang.NullPointerException
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.Activity.findViewById\untime(1958):  at java.lang.Class.newInstanceImpl(Native Method)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at java.lang.Class.newInstance(Class.java:1429)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
05-31 17:53:19.730: E/AndroidRuntime(1958):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
05-31 17:53:19.730: E/AndroidRuntime(1958):     ... 11 more

score 2 · Accepted Answer

在您声明的 Login.xml 中

<TextView
    android:id="@+id/LinkToRegisterScreen"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"/>

并同时映射 LoginActivity1.java

 btnLinkToRegistrScrn = (Button) findViewById(R.id.LinkToRegisterScreen);

所以只需更改TextView为Button

<Button
    android:id="@+id/LinkToRegisterScreen"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"/>

score 1 · Accepted Answer

Change Your LoginActivity1 Activity as:

public class LoginActivity1 extends Activity {

    Button btnLinkToRegistrScrn;
    Button loginbtn1;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
     setContentView(R.layout.login);
     addListenerOnButton();
        // Link to Register Screen 
        btnLinkToRegistrScrn = (Button) findViewById(R.id.LinkToRegisterScreen); 
        btnLinkToRegistrScrn.setOnClickListener(new View.OnClickListener() { 
           @Override
            public void onClick(View v) { 
                Intent i = new Intent(v.getContext(), TrekEyesAndroidActivity.class); 
              //  i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(i);
                } 
       }); 
   }
    public void addListenerOnButton() {

        //final Context context2 = this;

            loginbtn1 = (Button) findViewById(R.id.btnLogin);

            loginbtn1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {

                Intent intent = new Intent(arg0.getContext(), DashboardActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                         startActivity(intent);   
            }

        });
    }
   }

and in xml change TextView to Button as

<Button
         android:id="@+id/LinkToRegisterScreen"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginTop="25dip"

            android:textColor="#21dbd4"
            android:textStyle="bold" 
            android:text="@string/noAccountRegisterME" />

score 1 · Accepted Answer

在你的 login.xml

<TextView
            android:id="@+id/LinkToRegisterScreen"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginTop="25dip"

            android:textColor="#21dbd4"
            android:textStyle="bold" 
            android:text="@string/noAccountRegisterME" />

android:id="@+id/LinkToRegisterScreen"它是 EditText 并且你正在这样做 btnLinkToLoginScrn = (Button) findViewById(R.id.LinkToLoginScreen);它将是空指针..

所以只需在 login.xml 中更改 Button 而不是 TextView

score 0 · Accepted Answer

0

我认为你应该集中大括号。你给代码添加 listeneraddListenerOnButton()

于 2012-06-05T06:18:16.770 回答

java - Android app force closes while going on another activity

4 回答 4

Related

Reference