所以现在我的应用程序(QR代码扫描程序)当我尝试运行时崩溃了 . 调试生成的错误消息是:
E / AndroidRuntime:FATAL EXCEPTION:main进程:com.example.a16007637.qrcodereader,PID:4032 java.lang.RuntimeException:无法启动活动ComponentInfo {com.example.a16007637.qrcodereader / com.example.a16007637.qrcodereader . MainActivity}:java.lang.ClassCastException:android.support.constraint.ConstraintLayout无法在android.app.ActivityThread.handleLaunchActivity(ActivityThread)的android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)中强制转换为android.widget.TextView . .java:2856)在android.app.Handler.dispatchMessage(Handler.java:)的android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1589)的android.app.ActivityThread.-wrap11(未知来源:0) 106)在android.app.Looper.loop(Looper.java:164)的android.app.ActivityThread.main(ActivityThread.java:6494),位于com.android的java.lang.reflect.Method.invoke(Native Method) .internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:438)at com.android.internal.os.ZygoteInit.main(ZygoteInit.jav) a:807)引起:java.lang.ClassCastException:android.support.constraint.ConstraintLayout无法在com.example.a16007637.qrcodereader.MainActivity.onCreate(MainActivity.java:33)的android下运行到android.widget.TextView位于Android.app.ActivityChread的android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)的android.app.Activity.performCreate(Activity.java:7000)上的.app.Activity.performCreate(Activity.java:7009) . 在Android.app.ActivityThread.ActivityThread $ H.handleMessage(ActivityThread)的android.app.ActivityThread.-wrap11(未知来源:0)android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)的performLaunchActivity(ActivityThread.java:2731) .java:1589)在android.app.AutT.Dop上运行android.os.Handler.dispatchMessage(Handler.java:106)(Looper.java:164)android.app.ActivityThread.main(ActivityThread.java:6494) at com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:438)的com.andr上的java.lang.reflect.Method.invoke(Native Method) oid.internal.os.ZygoteInit.main(ZygoteInit.java:807)
引起我注意的主要是这一行:
ConstraintLayout无法强制转换为android.widget.TextView
我试图对此进行更多研究,但遗憾的是,我在网上找到的所有答案对我都不起作用 .
我的MainActivity.java代码是:
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import android.view.View;
import com.google.zxing.integration.android.IntentIntegrator;
import com.google.zxing.integration.android.IntentResult;
import org.json.JSONException;
import org.json.JSONObject;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private Button Scan;
private TextView QR_output;
private IntentIntegrator ScanCode;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Defines the Scan button
Scan = findViewById(R.id.Scan);
// defines the output for text
QR_output = findViewById(R.id.output);
// looks for the user clicking "Scan"
Scan.setOnClickListener(this);
ScanCode = new IntentIntegrator(this);
// Means the scan button will actually do something
Scan.setOnClickListener(this);
}
// will scan the qr code and reveal its secrets
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
if (result != null) {
// if an empty QR code gets scanned it returns a message to the user
//if qr contains data
if (result.getContents() == null) {
Toast.makeText(this, "This QR code is empty.", Toast.LENGTH_LONG).show();
} else try {
//converting the data to json
JSONObject obj = new JSONObject(result.getContents());
//setting values to textviews
QR_output.setText(obj.getString("name"));
} catch (JSONException e) {
e.printStackTrace();
//if control comes here
//that means the encoded format not matches
//in this case you can display whatever data is available on the qrcode
//to a toast
Toast.makeText(this, result.getContents(), Toast.LENGTH_LONG).show();
}
} else {
super.onActivityResult(requestCode, resultCode, data);
}
}
@Override
public void onClick(View view) {
//initiating the qr code scan
ScanCode.initiateScan();
}
}
我的XML文件在这里:
<?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:id="@+id/output"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:id="@+id/Scan"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="148dp"
android:layout_marginTop="514dp"
android:layout_marginEnd="148dp"
android:layout_marginBottom="5dp"
android:text="@string/Scan"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<TextView
android:id="@+id/QROutput"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="172dp"
android:layout_marginTop="358dp"
android:layout_marginEnd="166dp"
android:layout_marginBottom="137dp"
android:text="output"
app:layout_constraintBottom_toTopOf="@+id/Scan"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
任何帮助解决这个问题将不胜感激 .
2 回答
您为TextView编写了错误的ID . 您编写的id指向XML上的ConstraintLayout对象 .
而不是(第31行):
写这个:
您已使用id
output
用于根布局 . 即ConstraintLayout
,它将为您提供ConstraintLayout
的参考 . 显然,ConstraintLayout
的引用不能存储在TextView
类型的变量中,如果完成,则抛出异常 .使用以下代码来引用您的
TextView