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我是android和java的新手。让我解释一下我的项目。我正在编写一个 Android 应用程序。我想创建一个数据库并从文本视图中插入、删除、修改数据。ListView并使用另一个活动显示这些数据。我的第一个问题是,如何将这些数据发送到另一个活动?其次,我找到了一些代码:

List<Comment> values = datasource.getAllComments();
ArrayAdapter<Comment> adapter = new ArrayAdapter<Comment>(this, android.R.layout.simple_list_item_1, values);
setListAdapter(adapter);

在这些代码之后,写入插入记录代码。对我来说这是错误的,因为没有记录以及如何使用getAllComments方法获取数据,请解释一下。第三,如何以更好的方式将数据插入数据库 - 如果有的话 - 我想说的是,我正在调用我的插入方法MainActivity

Contact contact = dbOperations.addContact(editName.getText().toString(), editSurname.getText().toString(), editPhone.getText().toString(), editEmail.getText().toString());

但我不想得到这样的参数。如果我接受参数联系并编写我的代码,例如:

ContentValues values = new ContentValues();
values.put(DBHelper.colName, contact.getName());
values.put(DBHelper.colSurname, contact.getSurname());
values.put(DBHelper.colPhone, contact.getPhone());
values.put(DBHelper.colEmail, contact.getEmail());

我应该如何在文本视图中获取参数(调用插入方法)MainActivity?我读了一篇关于它的文章,我发现了这段代码:

db.addContact(new Contact("Srinivas", "9199999999"));

addContactString 方法带有联系参数,那么如果这段代码为真,他如何写值。

第四个也是最后一个问题是,

我的 logcat 错误:

08-26 19:21:06.639    9661-9661/? I/art﹕ Not late-enabling -Xcheck:jni (already on) 08-26 19:21:06.663    9661-9668/? E/art﹕ Failed writing handshake bytes (-1 of 14): Broken pipe 08-26 19:21:06.663    9661-9668/? I/art﹕ Debugger is no longer active 08-26 19:21:06.705    9661-9661/? D/AndroidRuntime﹕ Shutting down VM 08-26 19:21:06.705    9661-9661/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: busra.contactdb, PID: 9661
    java.lang.RuntimeException: Unable to start activity ComponentInfo{busra.contactdb/busra.contactdb.ContactActivity}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            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:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
     Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
            at android.app.ListActivity.onContentChanged(ListActivity.java:243)
            at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:382)
            at android.app.Activity.setContentView(Activity.java:2145)
            at busra.contactdb.ContactActivity.onCreate(ContactActivity.java:43)
            at android.app.Activity.performCreate(Activity.java:5990)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            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:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 08-26 19:26:06.781    9661-9661/? I/Process﹕ Sending signal. PID: 9661 SIG: 9

我不知道问题是什么。这一行:

at busra.contactdb.ContactActivity.onCreate(ContactActivity.java:43)

点此代码:

setContentView(R.layout.activity_contact);

我在 setAdapter 方法上遇到空指针异常。这是我的 ContactActivity:

public class ContactActivity extends Activity{

public static final String SEND_NAME= "";
public static final String SEND_SURNAME= "";
public static final String SEND_PHONE= "";
public static final String SEND_EMAIL= "";

DatabaseOperations dbOperations;
List values = new ArrayList();

@Override
    protected void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_contact);

    findViewAllIDs();

    dbOperations = new DatabaseOperations(this);
    dbOperations.openDB();


    values = dbOperations.getAllContacts();
    ArrayAdapter adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1,values);


    list.setAdapter(adapter);

    View v = findViewById(R.id.listButton);
    v.setOnClickListener(new View.OnClickListener() {

        public void onClick(View arg0) {
            if (arg0.getId() == R.id.listButton) {
                //define new intent to DisplayActivity

                Intent intent = new Intent(ContactActivity.this, DisplayActivity.class);
                String sendName = values.get(0).toString();
                intent.putExtra(SEND_NAME, sendName);


                String sendSurname = values.get(1).toString();
                intent.putExtra(SEND_SURNAME, sendSurname);


                String sendPhone = values.get(2).toString();
                intent.putExtra(SEND_PHONE, sendPhone);


                String sendEmail = values.get(3).toString();
                intent.putExtra(SEND_EMAIL, sendEmail);


                //start the second activity
                startActivity(intent);
            }
        }
    });


    btnAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            add();
        }
    });

    btnDelete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            delete();
        }
    });
    btnModify.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            // modify();
        }
    });

}

public void add(){
         ArrayAdapter adapter1 = (ArrayAdapter) list.getAdapter();
      // dbOperations.addContact(new Contact());


          Contact contact = dbOperations.addContact(editName.getText().toString(),
                  editSurname.getText().toString(),editPhone.getText().toString(),
                  editEmail.getText().toString());

          adapter1.add(contact);
          adapter1.notifyDataSetChanged();

}
public void delete(){
    Contact contact = null;
      ArrayAdapter adapter1 = (ArrayAdapter) list.getAdapter();
      if(list.getAdapter().getCount() > 0){
          contact = (Contact) list.getAdapter().getItem(0);
          dbOperations.deleteContact(contact);
          adapter1.remove(contact);
          adapter1.notifyDataSetChanged();
      }
}
public void modify () {
       Contact contact = null;
      // ArrayAdapter adapter1 = (ArrayAdapter) getListAdapter();
      if (getListAdapter().getCount() > 0) {
          contact = (Contact) getListAdapter().getItem(0);
          dbOperations.modifyContact(contact);

          adapter1.notifyDataSetChanged();
      }

我在 ContactActivity 的第二个布局 xml 中调用 ListView。list = (ListView) findViewById(android.R.id.list); 这是真的 ? 编辑: 我解决了我的问题,但不幸的是我找不到任何解决方案。如何将数据库记录传递给第二个活动并在其中显示?

activity_contact.xml

<?xml version= "1.0" encoding = "utf-8"?>
<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="wrap_content"
    android:orientation="vertical"
    tools:context=". MainActivity">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="15sp"
        android:text="@string/name"/>
    <EditText
        android:id="@+id/editName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPersonName"
        android:ems="10"
        android:layout_gravity="end"
        android:singleLine="true">
        <requestFocus/>
    </EditText>



    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/Surname"
        android:textSize="17sp"/>
    <EditText
        android:id="@+id/editSurname"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textPersonName"
        android:ems="10"
        android:layout_gravity="end"
        android:singleLine="true">

    </EditText>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/Phone"
        android:textSize="17sp"/>

    <EditText
        android:id="@+id/editPhone"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="phone"
        android:layout_gravity="bottom"
        android:singleLine="true">

    </EditText>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/email"
        android:textSize="17sp"/>

    <EditText
        android:id="@+id/editEmail"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textEmailAddress"
        android:layout_gravity="bottom"
        android:singleLine="true">

    </EditText>

    <Button
        android:id="@+id/add"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/add"
        android:textColor="#000066"
        android:textStyle="bold"
        android:textSize="15sp"
        android:layout_gravity="center_horizontal"/>

    <Button
        android:id="@+id/delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/delete"
        android:textColor="#000066"
        android:textStyle="bold"
        android:textSize="15sp"
        android:layout_gravity="center_horizontal"/>
    <Button
        android:id="@+id/modify"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/modify"
        android:textColor="#000066"
        android:textStyle="bold"
        android:textSize="15sp"
        android:layout_gravity="center_horizontal"/>
    <Button
        android:id="@+id/listButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/list"
        android:textColor="#000066"
        android:textStyle="bold"
        android:textSize="15sp"
        android:layout_gravity="center_horizontal"/>
    <TextView
        android:id="@+id/count_records"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="bold"
        android:textSize="13sp"/>

</LinearLayout>

list_contact_info.xml

<?xml version="1.0" encoding="utf-8"?> 
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

   <ListView
    android:id="@android:id/list"
    android:layout_width="wrap_content"
    android:layout_height="467dp"> </ListView>

    <Button
        android:id="@+id/back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/btnBack"
        android:textColor="#000066"
        android:textStyle="bold"
        android:textSize="15sp"
        android:layout_gravity="right|bottom"
        >
    </Button> 
     </FrameLayout>

任何帮助表示赞赏。

4

1 回答 1

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哦,这里有很多不同的问题。让我们从您的第一个问题开始:如果您希望将数据从一个活动发送到另一个活动,您应该考虑创建一个可以实例化的类。实例(Java 对象)保存所有数据,并且可以从不同的活动中访问。

所以如果你正在处理评论,你应该创建一个这样的评论类:

public class Comment implements Parcelable {

    private int commentId;
    private String commentTitle;
    private String commentText;

    // constructor
    public Comment() {

    } 

    // setters
    public void setCommentId(int id) {
        this.commentId = id;
    }

    public void setCommentTitle(String title) {
        this.commentTitle = title;
    }

    public void setCommentText(String text) {
        this.commentText = text;
    }

    // getters
    public int getCommentId() {
        return commentId;
    }

    public String getCommentTitle() {
        return commentId;
    }

    public String getCommentText() {
        return commentId;
    }

    // 99.9% of the time you can just ignore this
    public int describeContents() {
        return 0;
    }

    // write your object's data to the passed-in Parcel
    public void writeToParcel(Parcel out, int flags) {
        out.writeInt(commentId);
        out.writeString(commentTitle);
        out.writeString(commentText);
    }

    // this is used to regenerate your object. All Parcelables must have a CREATOR that implements these two methods
    public static final Parcelable.Creator<MyParcelable> CREATOR = new Parcelable.Creator<MyParcelable>() {
        public Comment createFromParcel(Parcel in) {
            return new Comment(in);
        }

        public Comment[] newArray(int size) {
            return new Comment[size];
        }
    };

    // example constructor that takes a Parcel and gives you an object populated with it's values
    private Comment(Parcel in) {
        commentId = in.readInt();
        commentTitle = in.readString();
        commentText = in.readString();
    }

}

然后在您的第一个活动中,您创建一个 Comment 类的实例,如下所示

Comment newComment = new Comment();

并用您喜欢的任何内容填充它:

newComment.setCommentTitle("My first comment");
newComment.setCommentText("Here goes my comment text...");

现在您可以将这个 Comment 对象传递给您的下一个活动,如下所示:

Intent i = new Intent(getActivity(), SecondActivity.class);
i.putExtra("newCommentKey", newComment); 
startActivity(i);

在您onCreate()调用的方法中的第二个活动中:

Intent i = getIntent();
Comment myComment = (Comment ) i.getParcelableExtra("newCommentKey");

并且可以通过 getter 获取所有内容,例如:

String titleOfComment = myComment.getCommentTitle();

祝你好运!

于 2015-09-22T14:33:09.070 回答