不启动 mainactivity

Question

The assembly occurs, but at startup it gives an error. What could be the problem? Help me. Both on the emulator and on the real device.

The assembly occurs, but at startup it gives an error. What could be the problem? Help me. Both on the emulator and on the real device. Here is the manifest

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="my.packpage">

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" 
/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" 
/>
<uses-permission 
android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".DownloadActivity"
        android:theme="@style/AppTheme"
        android:excludeFromRecents="true"
        android:taskAffinity="">

        <intent-filter>
            <action android:name="android.intent.action.SEND" />
            <category android:name="android.intent.category.DEFAULT" />
            <data android:mimeType="text/plain" />
        </intent-filter>

    </activity>

    <receiver

android:name=".DownloadFinishedReceiver"
        android:exported="true"
        android:process=".dlFinished">
        <intent-filter>
            <action 
android:name="android.intent.action.DOWNLOAD_COMPLETE" />
        </intent-filter>
    </receiver>
</application>

</manifest>

Here is the Activity_Main.xml

<?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:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="16dp"
    android:layout_marginLeft="16dp"
    android:text="@string/wel"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.051" />

 </android.support.constraint.ConstraintLayout>

Here is the MainActivity.java

package my.packpage;


import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
 }
 }

Answer 1

providing the error message generated would be the first step in finding the answer.. you may need to edit the question

Answer 2

first debug the application to know where the real problem is. Then post that error here