从 mysql 检索数据时应用崩溃
App crashing while retrieving data from mysql
大家好，我是 android 工作室的新手，所以我还在学习中。但是今天我遇到了一些我无法解决的事情。每次我在 Asyntax 中执行一个 sql 查询，如 "select * from databasename"，并在崩溃时执行类似 while(rs.next) 我的应用程序 keeps 的操作。我确定我从数据库建立了连接。
ps。我什至尝试了严格模式来查询主要但相同的结果 keeps crashing
我已经尝试了所有在线教程，以至于我复制了每一个东西并下载了它们的源代码，但我最终得到了相同的结果。
这是我的MainActivity.java
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btnShow = findViewById(R.id.btnShow);
btnShow.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
GetData retrieveData = new GetData();
retrieveData.execute();
}
});
}
private class GetData extends AsyncTask<String,String,String>{
String msg="";
final TextView textShow = findViewById(R.id.txtView1);
final TextView textShow1 = findViewById(R.id.txtView);
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://" + ConnectURL.DATABASE_URL + "/" + ConnectURL.DATABASE_NAME;
@Override
protected void onPreExecute(){
String Xmsg="Connecting to database...";
textShow.setText(Xmsg);
}
@Override
protected String doInBackground(String... params) {
Connection conn=null;
Statement stmt=null;
try {
Class.forName(JDBC_DRIVER);
conn = DriverManager.getConnection(DB_URL, ConnectURL.USERNAME, ConnectURL.PASSWORD);
stmt = conn.createStatement();
String sql = "Select * from poultryinfo";
ResultSet rs = stmt.executeQuery(sql);
ResultSetMetaData rmrs = rs.getMetaData();
msg="Connection completed";
while(rs.next()) {
msg += rmrs.getColumnName(2) + ":" + rs.getString("valName") + "\n";
}
textShow1.setText(msg);
rs.close();
stmt.close();
conn.close();
} catch (SQLException connError){
msg="An exception was thrown JDBC"+ connError.toString();
connError.printStackTrace();
} catch (ClassNotFoundException e) {
msg = "A class not found exception" + e.toString();
e.printStackTrace();
} finally {
try {
if (stmt != null) {
stmt.close();
}
} catch (SQLException e) {
e.printStackTrace();
msg = e.toString();
}
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
msg = e.toString();
}
}
return null;
}
@Override
protected void onPostExecute(String msg){
textShow.setText(this.msg);
}
}
}
这是我的 xml 文件，我认为这没有任何问题。
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/txtView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="154dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="154dp"
android:text="Hello World!"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/btnShow" />
<TextView
android:id="@+id/txtView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="154dp"
android:layout_marginTop="12dp"
android:layout_marginEnd="154dp"
android:text="Hello World!"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/txtView1" />
<Button
android:id="@+id/btnShow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="148dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="148dp"
android:text="@string/show"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
这些是 logcat 我得到的
10-08 18:33:58.620 25502-25502/? E/Zygote: v2
10-08 18:33:58.620 25502-25502/? E/Zygote: accessInfo : 0
10-08 18:34:00.250 25502-25502/com.example.jade.connectionpractice E/Qmage:
isQIO : stream is not a QIO file
10-08 18:34:02.830 25502-25813/com.example.jade.connectionpractice
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Process: com.example.jade.connectionpractice, PID: 25502
java.lang.RuntimeException: An error occurred while executing
doInBackground()
at android.os.AsyncTask.done(AsyncTask.java:309)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:8355)
at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:1327)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.support.constraint.ConstraintLayout.requestLayout(ConstraintLayout.java:3172)
at android.view.View.requestLayout(View.java:20170)
at android.widget.TextView.checkForRelayout(TextView.java:8425)
at android.widget.TextView.setText(TextView.java:5011)
at android.widget.TextView.setText(TextView.java:4836)
at android.widget.TextView.setText(TextView.java:4811)
at com.example.jade.connectionpractice.MainActivity$GetData.doInBackground(MainActivity.java:65)
at com.example.jade.connectionpractice.MainActivity$GetData.doInBackground(MainActivity.java:33)
at android.os.AsyncTask.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
堆栈跟踪中的消息已向您解释了问题：
Only the original thread that created a view hierarchy can touch its views
这告诉我您正在尝试从非 UI 线程操作视图（例如更新文本）。执政官：
textShow1.setText(msg);
解法：
在 doInBackground 之后，onPostExecute 在 UI 线程上运行，所以将 textShow1.setText(msg); 移到那里并使 doInBackground return msg 而不是 null
如果您想在 doInBackground 内进行 UI 操作，您可以使用 runOnUiThread 如下
@Override
protected String doInBackground(String... params) {
runOnUiThread(new Runnable() {
public void run() {
//do your UI operations here
textShow1.setText(msg);
}
});
}
大家好，我是 android 工作室的新手，所以我还在学习中。但是今天我遇到了一些我无法解决的事情。每次我在 Asyntax 中执行一个 sql 查询，如 "select * from databasename"，并在崩溃时执行类似 while(rs.next) 我的应用程序 keeps 的操作。我确定我从数据库建立了连接。
ps。我什至尝试了严格模式来查询主要但相同的结果 keeps crashing
我已经尝试了所有在线教程，以至于我复制了每一个东西并下载了它们的源代码，但我最终得到了相同的结果。
这是我的MainActivity.java
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btnShow = findViewById(R.id.btnShow);
btnShow.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
GetData retrieveData = new GetData();
retrieveData.execute();
}
});
}
private class GetData extends AsyncTask<String,String,String>{
String msg="";
final TextView textShow = findViewById(R.id.txtView1);
final TextView textShow1 = findViewById(R.id.txtView);
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://" + ConnectURL.DATABASE_URL + "/" + ConnectURL.DATABASE_NAME;
@Override
protected void onPreExecute(){
String Xmsg="Connecting to database...";
textShow.setText(Xmsg);
}
@Override
protected String doInBackground(String... params) {
Connection conn=null;
Statement stmt=null;
try {
Class.forName(JDBC_DRIVER);
conn = DriverManager.getConnection(DB_URL, ConnectURL.USERNAME, ConnectURL.PASSWORD);
stmt = conn.createStatement();
String sql = "Select * from poultryinfo";
ResultSet rs = stmt.executeQuery(sql);
ResultSetMetaData rmrs = rs.getMetaData();
msg="Connection completed";
while(rs.next()) {
msg += rmrs.getColumnName(2) + ":" + rs.getString("valName") + "\n";
}
textShow1.setText(msg);
rs.close();
stmt.close();
conn.close();
} catch (SQLException connError){
msg="An exception was thrown JDBC"+ connError.toString();
connError.printStackTrace();
} catch (ClassNotFoundException e) {
msg = "A class not found exception" + e.toString();
e.printStackTrace();
} finally {
try {
if (stmt != null) {
stmt.close();
}
} catch (SQLException e) {
e.printStackTrace();
msg = e.toString();
}
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
msg = e.toString();
}
}
return null;
}
@Override
protected void onPostExecute(String msg){
textShow.setText(this.msg);
}
}
}
这是我的 xml 文件，我认为这没有任何问题。
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/txtView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="154dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="154dp"
android:text="Hello World!"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/btnShow" />
<TextView
android:id="@+id/txtView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="154dp"
android:layout_marginTop="12dp"
android:layout_marginEnd="154dp"
android:text="Hello World!"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/txtView1" />
<Button
android:id="@+id/btnShow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="148dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="148dp"
android:text="@string/show"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
这些是 logcat 我得到的
10-08 18:33:58.620 25502-25502/? E/Zygote: v2
10-08 18:33:58.620 25502-25502/? E/Zygote: accessInfo : 0
10-08 18:34:00.250 25502-25502/com.example.jade.connectionpractice E/Qmage:
isQIO : stream is not a QIO file
10-08 18:34:02.830 25502-25813/com.example.jade.connectionpractice
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Process: com.example.jade.connectionpractice, PID: 25502
java.lang.RuntimeException: An error occurred while executing
doInBackground()
at android.os.AsyncTask.done(AsyncTask.java:309)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:8355)
at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:1327)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.view.View.requestLayout(View.java:20170)
at android.support.constraint.ConstraintLayout.requestLayout(ConstraintLayout.java:3172)
at android.view.View.requestLayout(View.java:20170)
at android.widget.TextView.checkForRelayout(TextView.java:8425)
at android.widget.TextView.setText(TextView.java:5011)
at android.widget.TextView.setText(TextView.java:4836)
at android.widget.TextView.setText(TextView.java:4811)
at com.example.jade.connectionpractice.MainActivity$GetData.doInBackground(MainActivity.java:65)
at com.example.jade.connectionpractice.MainActivity$GetData.doInBackground(MainActivity.java:33)
at android.os.AsyncTask.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
堆栈跟踪中的消息已向您解释了问题：
Only the original thread that created a view hierarchy can touch its views
这告诉我您正在尝试从非 UI 线程操作视图（例如更新文本）。执政官：
textShow1.setText(msg);
解法：
在 doInBackground 之后，onPostExecute 在 UI 线程上运行，所以将 textShow1.setText(msg); 移到那里并使 doInBackground return msg 而不是 null
如果您想在 doInBackground 内进行 UI 操作，您可以使用 runOnUiThread 如下
@Override
protected String doInBackground(String... params) {
runOnUiThread(new Runnable() {
public void run() {
//do your UI operations here
textShow1.setText(msg);
}
});
}