嗨，我是 Android 开发的新手。我创建了这个活动，似乎每次我点击这个活动中的一个按钮。我不断收到 Activity LogCat 错误的无法执行方法。
这是我的活动 Java 文件
public class Add_Edit_Cows extends Activity {
Button cradd, credit, crdelete, crview;
EditText cowids, sire, dam, months, dates, years;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add__edit__cows);
cradd = (Button) findViewById(R.id.addcow);
cowids = (EditText) findViewById(R.id.cowid);
sire = (EditText) findViewById(R.id.sire);
dam = (EditText) findViewById(R.id.dam);
months = (EditText) findViewById(R.id.DOBM);
dates = (EditText) findViewById(R.id.DOBd);
years = (EditText) findViewById(R.id.DOBy);
credit = (Button) findViewById(R.id.editcow);
crdelete = (Button) findViewById(R.id.removecow);
crview = (Button) findViewById(R.id.viewcows);
}
public void addcow (View view) {
Cowsdatabase cowsdb = new Cowsdatabase(this, null, null, 1);
int Cown = Integer.parseInt(cowids.getText().toString());
String Sire = sire.getText().toString();
String Dam = dam.getText().toString();
int Month = Integer.parseInt(months.getText().toString());
int Date = Integer.parseInt(dates.getText().toString());
int Year = Integer.parseInt(years.getText().toString());
cow Cow = new cow(Integer.parseInt(cowids.getText().toString()), Sire, Dam, Month, Date, Year);
cowsdb.addcow(Cow);
cowids.setText("");
sire.setText("");
dam.setText("");
months.setText("");
dates.setText("");
years.setText("");
}
public void editcow(View view) {
Cowsdatabase cowsdb = new Cowsdatabase(this, null, null, 1);
cow Cow =
cowsdb.findcow(Integer.parseInt(cowids.getText().toString()));
if (Cow != null) {
sire.setText(String.valueOf(Cow.getSire()));
dam.setText(String.valueOf(Cow.getDam()));
months.setText(String.valueOf(Cow.getMonth()));
dates.setText(String.valueOf(Cow.getDate()));
years.setText(String.valueOf(Cow.getYear()));
} else {
cowids.setText("No Match Found");
}
}
public void dcow (View view) {
Cowsdatabase cowsdb = new Cowsdatabase(this, null, null, 1);
boolean result = cowsdb.deleteCow(Integer.parseInt(cowids.getText().toString()));
if (result)
{
cowids.setText("Record Deleted");
sire.setText("");
dam.setText("");
months.setText("");
dates.setText("");
years.setText("");
}
else
cowids.setText("No Match Found");
}
public void viewcow (View view){
startActivity(new Intent("Ag.Access.Viewcows"));
}
}
LogCat 错误消息：
10-15 20:02:51.735: E/AndroidRuntime(7738): FATAL EXCEPTION: main
10-15 20:02:51.735: E/AndroidRuntime(7738): java.lang.IllegalStateException: Could not execute method of the activity
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.view.View$1.onClick(View.java:3591)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.view.View.performClick(View.java:4084)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.view.View$PerformClick.run(View.java:16966)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.os.Handler.handleCallback(Handler.java:615)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.os.Handler.dispatchMessage(Handler.java:92)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.os.Looper.loop(Looper.java:137)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-15 20:02:51.735: E/AndroidRuntime(7738): at java.lang.reflect.Method.invokeNative(Native Method)
10-15 20:02:51.735: E/AndroidRuntime(7738): at java.lang.reflect.Method.invoke(Method.java:511)
10-15 20:02:51.735: E/AndroidRuntime(7738): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-15 20:02:51.735: E/AndroidRuntime(7738): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-15 20:02:51.735: E/AndroidRuntime(7738): at dalvik.system.NativeStart.main(Native Method)
10-15 20:02:51.735: E/AndroidRuntime(7738): Caused by: java.lang.reflect.InvocationTargetException
10-15 20:02:51.735: E/AndroidRuntime(7738): at java.lang.reflect.Method.invokeNative(Native Method)
10-15 20:02:51.735: E/AndroidRuntime(7738): at java.lang.reflect.Method.invoke(Method.java:511)
10-15 20:02:51.735: E/AndroidRuntime(7738): at android.view.View$1.onClick(View.java:3586)
10-15 20:02:51.735: E/AndroidRuntime(7738): ... 11 more
10-15 20:02:51.735: E/AndroidRuntime(7738): Caused by: java.lang.NullPointerException
10-15 20:02:51.735: E/AndroidRuntime(7738): at ag.access.cowsdb.Cowsdatabase.addcow(Cowsdatabase.java:64)
10-15 20:02:51.735: E/AndroidRuntime(7738): at ag.access.Add_Edit_Cows.addcow(Add_Edit_Cows.java:48)
10-15 20:02:51.735: E/AndroidRuntime(7738): ... 14 more
我的 XML 文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="ag.access"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name`"`enter code here`
android:theme="@style/AppTheme" >
<activity
android:name="ag.access.MainActivity"
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:name="ag.access.Farming"
android:label="@string/title_activity_farming"
android:parentActivityName="ag.access.MainActivity" >
<intent-filter>
<action android:name="ag.access.Farming" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="ag.access.MainActivity" />
</activity>
<activity
android:name="ag.access.Dairy"
android:label="@string/title_activity_dairy"
android:parentActivityName="ag.access.MainActivity" >
<intent-filter>
<action android:name="ag.access.Dairy" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="ag.access.MainActivity" />
</activity>
<activity
android:name="ag.access.Daily_log"
android:label="@string/title_activity_daily_log"
android:parentActivityName="ag.access.Dairy" >
<intent-filter>
<action android:name="ag.access.Daily_log" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="ag.access.Dairy" />
</activity>
<activity
android:name="ag.access.Viewlogs"
android:label="@string/title_activity_viewlogs"
android:parentActivityName="ag.access.Daily_log" >
<intent-filter>
<action android:name="ag.access.Viewlogs" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="ag.access.Daily_log" />
</activity>
<activity
android:name="ag.access.Add_Edit_Cows"
android:label="@string/title_activity_add__edit__cows"
android:parentActivityName="ag.access.Dairy" >
<intent-filter>
<action android:name="ag.access.Add_Edit_Cows" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="ag.access.Dairy" />
</activity>
<activity
android:name="ag.access.Viewcows"
android:label="@string/title_activity_viewcows"
android:parentActivityName="ag.access.Add_Edit_Cows" >
<intent-filter>
<action android:name="ag.access.Viewcows" /
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="ag.access.Add_Edit_Cows" />
</activity>
</application>
</manifest>
我的 Add_Edit_Cows 活动
<ScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
tools:context=".Add_Edit_Cows" >
<TextView
android:id="@+id/textView1"
android:layout_width="280dp"
android:layout_height="wrap_content"
android:text="Add Edit Delete Cows"
android:textAppearance="?android:attr/textAppearanceLarge" />
<EditText
android:id="@+id/cowid"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="number"
android:hint="@string/cowid" />
<EditText
android:id="@+id/sire"
android:layout_width="280dp"
android:layout_height="wrap_content"
android:inputType="text"
android:hint="@string/sire"/>
<EditText
android:id="@+id/dam"
android:layout_width="280dp"
android:layout_height="wrap_content"
android:inputType="text"
android:hint="@string/dam"/>
<EditText
android:id="@+id/DOBM"
android:layout_width="280dp"
android:layout_height="wrap_content"
android:inputType="number"
android:hint="@string/DOBM"/>
<EditText
android:id="@+id/DOBd"
android:layout_width="280dp"
android:layout_height="wrap_content"
android:inputType="number"
android:hint="@string/DOBD"/>
<EditText
android:id="@+id/DOBy"
android:layout_width="280dp"
android:layout_height="wrap_content"
android:inputType="number"
android:hint="@string/DOBY"/>
<Button
android:id="@+id/addcow"
android:layout_width="261dp"
android:layout_height="wrap_content"
android:onClick="addcow"
android:text="@string/baddcow" />
<Button
android:id="@+id/editcow"
android:layout_width="261dp"
android:layout_height="wrap_content"
android:onClick="editcow"
android:text="@string/editcow" />
<Button
android:id="@+id/removecow"
android:layout_width="261dp"
android:layout_height="wrap_content"
android:onClick="dcow"
android:text="@string/deletecow" />
<Button
android:id="@+id/viewcows"
android:layout_width="261dp"
android:layout_height="wrap_content"
android:onClick="viewcow"
android:text="@string/viewc" />
</LinearLayout>
</ScrollView>
牛数据库.java
package ag.access.cowsdb;
import ag.access.cowsdb.provider.Cows_Provider;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class Cowsdatabase extends SQLiteOpenHelper {
private ContentResolver cowcr;
public Cowsdatabase(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
}
public static final String Key_id = "_id";
public static final String Key_Cow = "Cowid";
public static final String Key_Sire = "Sire";
public static final String Key_Dam = "Dam";
public static final String Key_DOBM = "Month";
public static final String Key_DOBD = "Date";
public static final String Key_DOBY = "Year";
private static final String DATABASE_NAME = "CowsDB";
public static final String DATABASE_TABLE = "Cows";
private static final int DATABASE_VERSION = 1;
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
String Create_Cows_Table = "CREATE TABLE" +
DATABASE_TABLE + "(" +
Key_id + "INTEGER PRIMARY KEY AUTOINCREMENT," +
Key_Cow + "INTEGER NOT NULL" +
Key_Sire + "TEXT NOT NULL," +
Key_Dam + "TEXT NOT NULL," +
Key_DOBM + "INTEGER NOT NULL," +
Key_DOBD + "INTEGER NOT NULL," +
Key_DOBY + "INTEGER NOT NULL," + ")";
db.execSQL(Create_Cows_Table);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXIST " + DATABASE_TABLE);
}
public void addcow(cow Cow) {
ContentValues values = new ContentValues();
values.put(Key_Cow, Cow.getCowid());
values.put(Key_Sire, Cow.getSire());
values.put(Key_Dam, Cow.getDam());
values.put(Key_DOBM, Cow.getMonth());
values.put(Key_DOBD, Cow.getDate());
values.put(Key_DOBY, Cow.getYear());
cowcr.insert(Cows_Provider.Content_Uri, values);
}
public cow findcow(int cowid) {
String[] projection = {Key_id, Key_Cow, Key_Sire, Key_Dam, Key_DOBM, Key_DOBD, Key_DOBY};
String selection = "cowid = \"" + cowid + "\"";
Cursor cursor = cowcr.query(Cows_Provider.Content_Uri, projection, selection, null, null);
cow cow = new cow();
if (cursor.moveToFirst()) {
cursor.moveToFirst();
cow.Setid(Integer.parseInt(cursor.getString(0)));
cow.SetCowid(Integer.parseInt(cursor.getString(1)));
cow.setSire(cursor.getString(2));
cow.setDam(cursor.getString(3));
cow.setMonth(Integer.parseInt(cursor.getString(4)));
cow.setDate(Integer.parseInt(cursor.getString(5)));
cow.setYear(Integer.parseInt(cursor.getString(6)));
cursor.close();
} else {
cow = null;
}
return cow;
}
public boolean deleteCow (int cowid) {
boolean result = false;
String selection = "cowid = \"" + cowid + "\"";
int rowsDeleted = cowcr.delete(Cows_Provider.Content_Uri, selection, null);
if (rowsDeleted > 0)
result = true;
return result;
}
}
对于 cradd 按钮，我希望它将来自 edittexts 的值添加到我的数据库中，然后由我的内容提供者接收对于 credit 按钮，我希望能够编辑数据库中的奶牛。对于 crdelete 按钮，我希望能够删除该数据库条目。对于 Crview，我希望它能够进行另一个活动，以便能够查看内容提供者。
就像我之前所说的那样，所有按钮都出现“无法执行活动的方法”LOGCAT 错误。
您的帮助将不胜感激。
谢谢