我被这个错误困住了，我不知道如何解决它。我有以下LoginActivity：
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class LoginActivity extends AppCompatActivity {
private String TAG = "LoginActivity";
private int REQUEST_SIGNUP = 0;
private EditText username;
private EditText password;
private Button login_btn;
int attempt_counter = 5;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
LoginButton();
}
public void LoginButton() {
username = (EditText)findViewById(R.id.input_email);
password = (EditText)findViewById(R.id.input_password);
login_btn = (Button)findViewById(R.id.btn_login);
login_btn.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
if(username.getText().toString().equals("user") &&
password.getText().toString().equals("pass") ) {
Toast.makeText(LoginActivity.this,"User and Password is correct",
Toast.LENGTH_SHORT).show();
Intent intent = new Intent(".MainActivity");
startActivity(intent);
} else {
Toast.makeText(LoginActivity.this,"User and Password is not correct",
Toast.LENGTH_SHORT).show();
}
}
}
);
}
}
如您所见，即时通讯扩展了“ AppCompactActivity”。如果我运行该应用程序，则会抛出该主题中提到的错误。如果我更新代码并将其更改为“扩展活动”，那么它将起作用。为什么会这样？
以下是我的清单文件，我认为它是正确的，否则即使我使用“扩展活动”，应用程序也永远不会运行：
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<!-- To auto-complete the email text field in the login form with the user's emails -->
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="android.permission.READ_PROFILE" />
<uses-permission android:name="android.permission.READ_CONTACTS" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<activity android:name=".LoginActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<action android:name="android.intent.action.VIEW" />
</intent-filter>
</activity>
<activity
android:name=".MainActivity"
android:label="@string/app_name_main" >
<intent-filter>
<action android:name=".MainActivity" />
</intent-filter>
</activity>
</application>
成绩文件：
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:28.0.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
//implementation 'com.android.support:multidex:1.0.3'
//implementation "org.apache.poi:poi:3.17"
//implementation "org.apache.poi:poi-ooxml:3.71"
implementation group: 'org.apache.poi', name: 'poi-ooxml', version: '4.0.1'
//implementation files('libs/poishadow-all.jar')
//implementation 'com.fasterxml:aalto-xml:1.0.0'
implementation 'com.android.support:design:28.0.0'
//implementation 'com.jakewharton:butterknife:8.5.1'
//annotationProcessor 'com.jakewharton:butterknife-compiler:8.5.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}
和堆栈跟踪：
2019-02-01 00:02:49.522 18723-18723/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.test.proj, PID: 18723
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.test.proj/com.test.proj.LoginActivity}: java.lang.ClassNotFoundException: Didn't find class "com.test.proj.LoginActivity" on path: DexPathList[[zip file "/data/app/com.test.proj-PMMv5uc0Z9RUZsO7uJBe_Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.test.proj-PMMv5uc0Z9RUZsO7uJBe_Q==/lib/x86, /system/lib, /vendor/lib]]
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2718)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.ClassNotFoundException: Didn't find class "com.test.proj.LoginActivity" on path: DexPathList[[zip file "/data/app/com.test.proj-PMMv5uc0Z9RUZsO7uJBe_Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.test.proj-PMMv5uc0Z9RUZsO7uJBe_Q==/lib/x86, /system/lib, /vendor/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:93)
at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
at android.app.Instrumentation.newActivity(Instrumentation.java:1173)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2708)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Suppressed: java.lang.NoClassDefFoundError: Failed resolution of: Landroid/support/v7/app/AppCompatActivity;
at java.lang.VMClassLoader.findLoadedClass(Native Method)
at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:738)
at java.lang.ClassLoader.loadClass(ClassLoader.java:363)
... 12 more
Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v7.app.AppCompatActivity" on path: DexPathList[[zip file "/data/app/com.test.proj-PMMv5uc0Z9RUZsO7uJBe_Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.test.proj-PMMv5uc0Z9RUZsO7uJBe_Q==/lib/x86, /system/lib, /vendor/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:93)
at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
... 15 more
如果它还有助于我也包括activity-login.xml，我在其中注释了一些字段，因为我认为它们导致了紧凑错误，尽管并非如此：
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fitsSystemWindows="true">
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="56dp"
android:paddingLeft="24dp"
android:paddingRight="24dp">
<ImageView android:src="@drawable/ic_test_icon"
android:layout_width="wrap_content"
android:layout_height="72dp"
android:layout_marginBottom="24dp"
android:layout_gravity="center_horizontal" />
<!-- Email Label -->
<!--<android.support.design.widget.TextInputLayout-->
<!--android:layout_width="match_parent"-->
<!--android:layout_height="wrap_content"-->
<!--android:layout_marginTop="8dp"-->
<!--android:layout_marginBottom="8dp"-->
<!--android:theme="@style/Theme.AppCompat">-->
<!--<android.support.design.widget.TextInputEditText-->
<!--android:id="@+id/input_email"-->
<!--android:layout_width="match_parent"-->
<!--android:layout_height="wrap_content"-->
<!--android:inputType="textEmailAddress"-->
<!--android:hint="Email" />-->
<!--</android.support.design.widget.TextInputLayout>-->
<!-- Password Label -->
<!--<android.support.design.widget.TextInputLayout-->
<!--android:layout_width="match_parent"-->
<!--android:layout_height="wrap_content"-->
<!--android:layout_marginTop="8dp"-->
<!--android:layout_marginBottom="8dp"-->
<!--android:theme="@style/Theme.AppCompat">-->
<!--<android.support.design.widget.TextInputEditText-->
<!--android:id="@+id/input_password"-->
<!--android:layout_width="match_parent"-->
<!--android:layout_height="wrap_content"-->
<!--android:inputType="textPassword"-->
<!--android:hint="Password"/>-->
<!--</android.support.design.widget.TextInputLayout>-->
<Button
android:id="@+id/btn_login"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginBottom="24dp"
android:padding="12dp"
android:text="Login"/>
<TextView android:id="@+id/link_signup"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="24dp"
android:text="No account yet? Create one"
android:gravity="center"
android:textSize="16dip"/>
</LinearLayout>
</ScrollView>
编辑：
添加了styles.xml
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
<item name="colorPrimary">@color/colorPrimary</item>
<item name="colorPrimaryDark">@color/colorPrimaryDark</item>
<item name="colorAccent">@color/colorAccent</item>
</style>
答案 0 :(得分：0)
在导入部分，如果可以检查是否导入了Activity和AppCompactActivity。请从导入中删除该活动，然后重新构建并运行。
答案 1 :(得分：0)
检查您的styles.xml
<style name="AppTheme" parent="**Theme.AppCompat**.Light.DarkActionBar">
<item name="colorPrimary">@color/colorPrimary</item>
<item name="colorPrimaryDark">@color/colorPrimaryDark</item>
<item name="colorAccent">@color/colorAccent</item>
</style>
您必须使用Theme.AppCompat
答案 2 :(得分：0)
最后！设法解决了...原来是罪魁祸首在我的gradle文件中。以下导入导致Android Studio无法识别紧凑导入或忽略它们...
的溶液以除去以下依赖
implementation group: 'org.apache.poi', name: 'poi-ooxml', version: '4.0.1'
，而是使用以下内容：
implementation 'org.apache.poi:poi-ooxml:3.9'