Question

我的应用意外停止了。这是我的代码。

package com.nisani.angel;

//import info.androidhive.jsonparsing.MainActivity.GetContacts;
import android.app.Activity;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.os.Bundle;
import android.util.Log; 
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
 import android.widget.EditText;
import android.widget.ShareActionProvider;
import android.widget.Toast;

public class MainActivity extends Activity {
EditText edit_name;
EditText edit_phone;
Button add_new=(Button)findViewById(R.id.button1);
SQLiteDatabase db=null;
String tag=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.i(tag, "1");
    try{

       db= openOrCreateDatabase("Mydb", MODE_PRIVATE, null);
       db.execSQL("create table if not exists myname(name varchar,mobile_no varchar)");

    }

    catch(NullPointerException e){

        Log.i(tag, "2");
    }
add_new.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View arg0) {
        edit_phone=(EditText)findViewById(R.id.phone);
        edit_name=(EditText)findViewById(R.id.name);
        String name1=edit_name.getText().toString();
        String mobile_no1=edit_phone.getText().toString();
        db.execSQL("insert into myname values('"+name1+"','"+mobile_no1+"')");
        db.close();

    }
});

Toast.makeText(this, "values inserted successfully.", Toast.LENGTH_LONG).show();

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    getMenuInflater().inflate(R.menu.action_bar_share_menu, menu);
            MenuItem item = menu.findItem(R.id.menu_item_share);

            ShareActionProvider myShareActionProvider = (ShareActionProvider) item.getActionProvider();

            Intent myIntent = new Intent();
            myIntent.setAction(Intent.ACTION_SEND);
            myIntent.putExtra(Intent.EXTRA_TEXT, " ");
            myIntent.setType("text/plain");

            myShareActionProvider.setShareIntent(myIntent);

            return true;
        }

}

这是我的日志猫。

 07-09 13:22:54.010: D/AndroidRuntime(2251): Shutting down VM
 07-09 13:22:54.010: W/dalvikvm(2251): threadid=1: thread exiting with     uncaught           exception (group=0xb2a96ba8)
 07-09 13:22:54.060: E/AndroidRuntime(2251): FATAL EXCEPTION: main
07-09 13:22:54.060: E/AndroidRuntime(2251): Process: com.nisani.angel, PID: 2251
07-09 13:22:54.060: E/AndroidRuntime(2251): java.lang.RuntimeException: Unable to     instantiate activity ComponentInfo{com.nisani.angel/com.nisani.angel.MainActivity}: java.lang.NullPointerException
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.os.Handler.dispatchMessage(Handler.java:102)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.os.Looper.loop(Looper.java:136)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.ActivityThread.main(ActivityThread.java:5017)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at java.lang.reflect.Method.invokeNative(Native Method)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at java.lang.reflect.Method.invoke(Method.java:515)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at dalvik.system.NativeStart.main(Native Method)
07-09 13:22:54.060: E/AndroidRuntime(2251): Caused by: java.lang.NullPointerException
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.Activity.findViewById(Activity.java:1884)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at com.nisani.angel.MainActivity.<init>(MainActivity.java:21)
 07-09 13:22:54.060: E/AndroidRuntime(2251):    at     java.lang.Class.newInstanceImpl(Native Method)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at     java.lang.Class.newInstance(Class.java:1208)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
07-09 13:22:54.060: E/AndroidRuntime(2251):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
07-09 13:22:54.060: E/AndroidRuntime(2251):     ... 11 more
07-09 13:23:02.440: I/Process(2251): Sending signal. PID: 2251 SIG: 9

它不起作用。如何纠正它。请尽可能尽快回复。它不起作用。如何纠正它。请尽可能尽快回复。它不起作用。如何纠正它。请尽快回复。

Answer 1

这个

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

必须在onCreate

之后setContentView(R.layout.activity_main);

查看来源@ http://androidxref.com/4.4.3_r1.1/xref/frameworks/base/core/java/android/app/Activity.java

1883    public View findViewById(int id) {
1884        return getWindow().findViewById(id); // returns null
1885    }

Answer 2

onCrete(){ 
setContentView(R.layout.activity_main);
Button add_new=(Button)findViewById(R.id.button1);//this event must be after your layout
...
...
}

Answer 3

设置如下：

public class MainActivity extends Activity {
 EditText edit_name;
 EditText edit_phone;
 Button add_new;
 SQLiteDatabase db=null;
 String tag=null;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  add_new=(Button)findViewById(R.id.button1);     // Add here
  Log.i(tag, "1");
  try{

   db= openOrCreateDatabase("Mydb", MODE_PRIVATE, null);
   db.execSQL("create table if not exists myname(name varchar,mobile_no varchar)");

  }

  catch(NullPointerException e){

    Log.i(tag, "2");
  }
 add_new.setOnClickListener(new View.OnClickListener() {

 @Override
 public void onClick(View arg0) {
    edit_phone=(EditText)findViewById(R.id.phone);
    edit_name=(EditText)findViewById(R.id.name);
    String name1=edit_name.getText().toString();
    String mobile_no1=edit_phone.getText().toString();
    db.execSQL("insert into myname values('"+name1+"','"+mobile_no1+"')");
    db.close();

 }
});

应用程序停止sqlite无法正常工作

3 个答案: