因此,当我尝试运行它时,我的应用程序(QR码扫描仪)当前崩溃。调试产生的错误消息是:
E / Android运行时:致命异常:主要 流程: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无法转换为 android.widget.TextView 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778) 在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 在android.app.ActivityThread.-wrap11(未知来源:0) 在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1589) 在android.os.Handler.dispatchMessage(Handler.java:106) 在android.os.Looper.loop(Looper.java:164) 在android.app.ActivityThread.main(ActivityThread.java:6494) 在java.lang.reflect.Method.invoke(本机方法) 在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:438) 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 造成原因:java.lang.ClassCastException:android.support.constraint.ConstraintLayout无法强制转换为 android.widget.TextView 在com.example.a16007637.qrcodereader.MainActivity.onCreate(MainActivity.java:33) 在android.app.Activity.performCreate(Activity.java:7009) 在android.app.Activity.performCreate(Activity.java:7000) 在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214) 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731) 在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 在android.app.ActivityThread.-wrap11(未知来源:0) 在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1589) 在android.os.Handler.dispatchMessage(Handler.java:106) 在android.os.Looper.loop(Looper.java:164) 在android.app.ActivityThread.main(ActivityThread.java:6494) 在java.lang.reflect.Method.invoke(本机方法) 在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:438) 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
引起我注意的主要内容是此行:
ConstraintLayout无法转换为android.widget.TextView
我尝试对此进行更多的研究,但不幸的是,我在网上发现的所有答案对我来说都行不通。
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>
任何解决此问题的帮助将不胜感激。
答案 0 :(得分:0)
您已将ID output
用于根目录布局。即ConstraintLayout
,它将为您提供ConstraintLayout
的参考。显然,对ConstraintLayout
的引用不能存储在类型为TextView
的变量中,如果完成,则会引发异常。
使用以下代码引用您的TextView
QR_output = findViewById(R.id.QROutput);
答案 1 :(得分:0)
您为TextView输入了错误的ID。您编写的ID指向XML上的ConstraintLayout对象。
代替(第31行):
QR_output = findViewById(R.id.output);
写下:
QR_output = findViewById(R.id.QROutput);