Question

有人可以帮我找出mustache背后的原因。

这是我的错误日志：

NullPointerException

我的主要活动＆＃39;文件：

8-13 23:27:33.924    4817-4817/? E/Zygote﹕ MountEmulatedStorage()
08-13 23:27:33.924    4817-4817/? E/Zygote﹕ v2
08-13 23:27:33.934    4817-4817/? E/SELinux﹕ [DEBUG] get_category: variable 
seinfo: default sensitivity: NULL, cateogry: NULL
08-13 23:27:34.024    4817-4817/com.kishore_kumar.call E/AndroidRuntime﹕ 
FATAL EXCEPTION: main
Process: com.kishore_kumar.call, PID: 4817
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo
{com.kishore_kumar.call/com.kishore_kumar.call.MainActivity}: 
java.lang.NullPointerException: Attempt to invoke virtual 
method 'android.view.View android.view.Window.findViewById(int)' on a null 
object reference
        at android.app.ActivityThread.performLaunchActivity
(ActivityThread.java:2515)
        at android.app.ActivityThread.handleLaunchActivity    
(ActivityThread.java:2723)
        at android.app.ActivityThread.access$900(ActivityThread.java:172)
        at android.app.ActivityThread$H.handleMessage
(ActivityThread.java:1422)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:145)
        at android.app.ActivityThread.main(ActivityThread.java:5832)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:1399)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual     
 method 'android.view.View android.view.Window.findViewById(int)' on a null 
 object reference
        at android.app.Activity.findViewById(Activity.java:2168)
        at com.kishore_kumar.call.MainActivity.<init>(MainActivity.java:21)
        at java.lang.reflect.Constructor.newInstance(Native Method)
        at java.lang.Class.newInstance(Class.java:1650)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
        at android.app.ActivityThread.performLaunchActivity
 (ActivityThread.java:2505)
        at android.app.ActivityThread.handleLaunchActivity  
 (ActivityThread.java:2723)
        at android.app.ActivityThread.access$900(ActivityThread.java:172)
        at android.app.ActivityThread$H.handleMessage
 (ActivityThread.java:1422)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:145)
        at android.app.ActivityThread.main(ActivityThread.java:5832)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:1399)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

这是我的Loader对象类文件：

package com.kishore_kumar.call;

import android.app.Activity;
import android.app.SearchManager;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.widget.SearchView;
import android.widget.*;

/**
* Simple one-activity app that takes a search term via the Action Bar
* and uses it as a query to search the contacts database via the Contactables
* table.
*/
public class MainActivity extends Activity {

public static final int CONTACT_QUERY_LOADER = 0;
    public static final String QUERY_KEY = "query";
    public EditText cn = (EditText) findViewById(R.id.mainEditText);
    String query = "";

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

    private void startQuery()
    {
        query = cn.getText().toString();
        // We need to create a bundle containing the query string to send along to the
        // LoaderManager, which will be handling querying the database and returning results.
        if(query!="")
        {
            Bundle bundle = new Bundle();
            bundle.putString(QUERY_KEY, query);

            ContactablesLoaderCallbacks loaderCallbacks = new     
                ContactablesLoaderCallbacks(this);

            // Start the loader with the new query, and an object that will 
            handle all callbacks.
                getLoaderManager().restartLoader(CONTACT_QUERY_LOADER, bundle, 
                        loaderCallbacks);
        }
    }
}

这是我的主要布局文件：

package com.kishore_kumar.call;

import android.app.Activity;
import android.app.LoaderManager;
import android.content.Context;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract.CommonDataKinds;
import android.util.Log;
import android.widget.TextView;

/**
* Helper class to handle all the callbacks that occur when interacting with 
loaders.  Most of the
* interesting code in this sample app will be in this file.
*/
public class ContactablesLoaderCallbacks implements 
        LoaderManager.LoaderCallbacks<Cursor> {

    Context mContext;

    public static final String QUERY_KEY = "query";

    public static final String TAG = "CLoaderCallbacks";

    public ContactablesLoaderCallbacks(Context context) {
        mContext = context;
    }
    @Override
    public Loader<Cursor> onCreateLoader(int loaderIndex, Bundle bundle) {
        // Where the Contactables table excels is matching text queries,
        // not just data dumps from Contacts db.  One search term is used to query
        // display name, email address and phone number.  In this case, the query was extracted
        // from an incoming intent in the handleIntent() method, via the
        // intent.getStringExtra() method.

        // BEGIN_INCLUDE(uri_with_query)
        String query = bundle.getString(QUERY_KEY);
        Uri uri = Uri.withAppendedPath(
            CommonDataKinds.Contactables.CONTENT_FILTER_URI, query);
        // END_INCLUDE(uri_with_query)


        // BEGIN_INCLUDE(cursor_loader)
        // Easy way to limit the query to contacts with phone numbers.
        String selection = CommonDataKinds.Contactables.HAS_PHONE_NUMBER + " = " + 1;

        // Sort results such that rows for the same contact stay together.
        String sortBy = CommonDataKinds.Contactables.LOOKUP_KEY;

        return new CursorLoader(
            mContext,  // Context
            uri,       // URI representing the table/resource to be queried
            null,      // projection - the list of columns to return.  Null means "all"
            selection, // selection - Which rows to return (condition rows must match)
            null,      // selection args - can be provided separately and subbed into selection.
            sortBy);   // string specifying sort order
        // END_INCLUDE(cursor_loader)
    }

    @Override
    public void onLoadFinished(Loader<Cursor> arg0, Cursor cursor) {
        TextView tv  = (TextView) ((Activity)mContext).findViewById(R.id.sampleOutput);
        if(tv == null) {
            Log.e(TAG, "TextView is null?!");
        } else if (mContext == null) {
            Log.e(TAG, "Context is null?");
        } else {
            Log.e(TAG, "Nothing is null?!");
        }

        // Reset text in case of a previous query
        tv.setText(mContext.getText(R.string.intro) + "\n\n");

        if (cursor.getCount() == 0) {
            return;
        }

        // Pulling the relevant value from the cursor requires knowing the column index to pull
        // it from.
        // BEGIN_INCLUDE(get_columns)
        int phoneColumnIndex = cursor.getColumnIndex
        (CommonDataKinds.Phone.NUMBER);
        int emailColumnIndex = cursor.getColumnIndex
        (CommonDataKinds.Email.ADDRESS);
        int nameColumnIndex = cursor.getColumnIndex
        (CommonDataKinds.Contactables.DISPLAY_NAME);
        int lookupColumnIndex = cursor.getColumnIndex  
        (CommonDataKinds.Contactables.LOOKUP_KEY);
        int typeColumnIndex = cursor.getColumnIndex
        (CommonDataKinds.Contactables.MIMETYPE);
        // END_INCLUDE(get_columns)

        cursor.moveToFirst();
        // Lookup key is the easiest way to verify a row of data is for the same
        // contact as the previous row.
        String lookupKey = "";
        do {
            // BEGIN_INCLUDE(lookup_key)
            String currentLookupKey = cursor.getString(lookupColumnIndex);
            if (!lookupKey.equals(currentLookupKey)) {
                String displayName = cursor.getString(nameColumnIndex);
                tv.append(displayName + "\n");
                lookupKey = currentLookupKey;
            }
            // END_INCLUDE(lookup_key)

            // BEGIN_INCLUDE(retrieve_data)
            // The data type can be determined using the mime type column.
            String mimeType = cursor.getString(typeColumnIndex);
            if (mimeType.equals(CommonDataKinds.Phone.CONTENT_ITEM_TYPE)) {
                tv.append("\tPhone Number: " + cursor.getString
               (phoneColumnIndex) + "\n");
            } else
            {
                tv.setText("selected contact has no phone number");
            }
            // END_INCLUDE(retrieve_data)

            // Look at DDMS to see all the columns returned by a query to  Contactables.
            // Behold, the firehose!
            for(String column : cursor.getColumnNames()) {
                Log.d(TAG, column + column + ": " +
                      cursor.getString(cursor.getColumnIndex(column)) + "\n");
            }
        } while (cursor.moveToNext());
    }

    @Override
    public void onLoaderReset(Loader<Cursor> cursorLoader) {
    }
}

我的ContactablesLoaderCallbacks文件中的这一行也会产生错误：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="top|left"
android:orientation="vertical" tools:context=".MainActivity">

    <TextView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:text="Please enter contact name:"
        android:textSize="36sp"/>
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Contact Name"
        android:id="@+id/mainEditText"
        android:textSize="20sp"/>
    <TextView
        android:text="@string/intro"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/sampleOutput"
        android:textSize="20sp"
        android:paddingTop="10dp"/>
</LinearLayout>

tv.setText(mContext.getText(R.string.intro) + "\n\n");

如果错误部分中存在输入错误，请原谅我：或者这是一张照片：

如果您想知道 - 这是来自Android开发者网站的应用示例的修改应用。我知道许可证，这只是我测试应用程序。

Answer 1

试试这个

public class MainActivity extends Activity {

    public static final int CONTACT_QUERY_LOADER = 0;
    public static final String QUERY_KEY = "query";
    public EditText cn;
    String query = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        cn = (EditText) findViewById(R.id.mainEditText);
                startQuery();
    }

        private void startQuery()
                {
            query = cn.getText().toString();
            // We need to create a bundle containing the query string to    
    send along to the
            // LoaderManager, which will be handling querying the database
    and returning results.
                        if(query!="")
                        {
            Bundle bundle = new Bundle();
            bundle.putString(QUERY_KEY, query);

            ContactablesLoaderCallbacks loaderCallbacks = new    
    ContactablesLoaderCallbacks(this);

            // Start the loader with the new query, and an object that will
    handle all callbacks.
            getLoaderManager().restartLoader(CONTACT_QUERY_LOADER, bundle,
    loaderCallbacks);
        }
                }
    }

java.lang.NullPointerException：尝试调用虚方法＆＃39; android.view.View android.view.Window.findViewById（int）＆＃39;在null对象引用上

1 个答案: