[英]java.lang.ClassCastException: android.widget.LinearLayout$LayoutParams cannot be cast to android.support.constraint.ConstraintLayout$LayoutParams
[英]java.lang.ClassCastException: android.support.constraint.ConstraintLayout cannot be cast to android.widget.TextView
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这样的:
E / AndroidRuntime:致命例外:主进程: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:无法将android.support.constraint.ConstraintLayout强制转换为android.app.ActivityThread.handleLaunchActivity(ActivityThread.android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)上的android.widget.TextView。 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 )的android.os.Looper.loop(Looper.java:164)的com.android.java.lang.reflect.Method.invoke(本机方法)的android.app.ActivityThread.main(ActivityThread.java:6494)的)。在com.android.internal.os.ZygoteInit.main(ZygoteInit.java :)上的internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:438): 807)由以下原因引起:java.lang.ClassCastException:android.support.constraint.ConstraintLayout无法在com.example.a16007637.qrcodereader.MainActivity.onCreate(MainActivity.java:33)上转换为com.example.a16007637.qrcodereader.MainActivity.onCreate(MainActivity.java:33) android.app.Activity.performCreate(Activity.java:7000)的.Activity.performCreate(Activity.java:7009)android.app.ActivityThread.performLaunchActivity(.android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214) android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)上的ActivityThread.java:2731)android.app.ActivityThread $ H.handleMessage(ActivityThread.java)上android.app.ActivityThread.-wrap11(未知源:0) :1589),位于android.os.Handler.dispatchMessage(Handler.java:106),位于android.os.Looper.loop(Looper.java:164),位于android.app.ActivityThread.main(ActivityThread.java:6494),位于Java com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:438)处的.lang.reflect.Method.invoke(本机方法) m.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
吸引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,我在网上找到的所有答案都对我不起作用。
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>
解决该问题的任何帮助将不胜感激。
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);
写这个:
QR_output = findViewById(R.id.QROutput);
您已将id output
用于您的根布局。 即ConstraintLayout
,它将为您提供ConstraintLayout
的参考。 显然,对ConstraintLayout
的引用不能存储在TextView
类型的变量中,如果完成,该变量将引发异常。
使用以下代码引用您的TextView
QR_output = findViewById(R.id.QROutput);
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