Develop Reference

application cannot be installed on API 21

I just made an application using Android Studio 3.6, I tested using API 29, the application can be installed, but when I ask my friend to test on his device (Android 6.0) the application is not installed, so my application can only be installed on Android 7.0 and above, I want old Android users to be able to use my application. This is build.gradle that I use
apply plugin: 'com.android.application'
apply plugin: 'com.google.gms.google-services'
android {
compileSdkVersion 29
buildToolsVersion "29.0.3"
defaultConfig {
applicationId "com.my.app"
minSdkVersion 21
targetSdkVersion 29
versionCode 10
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.appcompat:appcompat:1.1.0'
...
}
I have tried to downgrade the target SDK but it still cannot be installed

Device Compatibility of my app

I created an Android application, but I cannot view it on play store and when I access it from web play store I found that:
Cette application n'est pas compatible avec votre appareil.
I don't know the reason of that
here is my build file
apply plugin: 'com.android.application'
android {
compileSdkVersion 17
buildToolsVersion '21.0.0'
compileOptions.encoding "ISO-8859-1"
defaultConfig {
applicationId "com.commande.soqop"
minSdkVersion 15
targetSdkVersion 18
versionCode 3
versionName "1.2"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
aaptOptions{
cruncherEnabled = false
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'org.apache.directory.studio:org.apache.commons.io:2.4'
}
I have tested on Samsung Tab 4 (Android 5.0) and Samsung S5 (Android 6)
How can I fix this issue?

Increase the targetSdkVersion of your app. The devices on which you tested might be above the version you mentioned in build.gradle.
Replace target SDK with the latest one :
apply plugin: 'com.android.application'
android {
compileSdkVersion 17
buildToolsVersion '26.0.2'
compileOptions.encoding "ISO-8859-1"
defaultConfig {
applicationId "com.commande.soqop"
minSdkVersion 15
targetSdkVersion 26
versionCode 3
versionName "1.2"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
aaptOptions{
cruncherEnabled = false
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'org.apache.directory.studio:org.apache.commons.io:2.4'
}

It will almost certainly be something in your manifest settings. Can you edit your question to show your AndroidManifest.xml?

App errors even when its a new empty project

The app works when I build it in my phone using Android Studio. But when I send it to low sdk device it doesn't work even when its sdk <=14
like Samsung s3 or s2.
apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "24.0.3"
defaultConfig {
applicationId "com.pc.zaid.zzz"
minSdkVersion 14
targetSdkVersion 23
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:23.4.0'
}

My android apk can not run on android 6.0

apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "23.0.3"
defaultConfig {
applicationId "com.example.aclientz.aclientzcds"
minSdkVersion 15
targetSdkVersion 23
versionCode 1
versionName "1.0"
}
buildTypes {
debug {
debuggable true
}
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:23.4.0'
}
I develop an android application in android studio.Created a signed buindle apk and install my phone (android 5.0) work perfactly but its not working in andoid 5.0+ version. How to avoid this problems, pLease give suggestion

Please Check for runtime permission if you have any permission uses camera or contact which require runtime permission (link)
or for checking purpose please set your targetsdk to 22

Android Studio telling me it cannot resolve symbols?

Android Studio was telling me it couldn't resolve some symbols in my code. After research, it was apparent that my project was API level 23, which wasnt compatible with some of the code. I decided to change it to API level 21.
Below is the previous code in my build.gradle file
apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "23.0.1"
defaultConfig {
applicationId "com.scriptdesigninc.test_app"
minSdkVersion 8
targetSdkVersion 23
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:23.0.1'
}
I was told that I have to change it to the following,
apply plugin: 'com.android.application'
android {
compileSdkVersion 21
buildToolsVersion "21.1.2"
defaultConfig {
applicationId "com.scriptdesigninc.test_app"
minSdkVersion 14
targetSdkVersion 21
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:22.2.0'
}
After I changed it, it told me I am missing the API package and that I have to download it, which I did. Then I clicked "retry" and it said it was unable to sync gradle project.
Please help, thank you in advance.

dependencies {
compile 'org.jbundle.util.osgi.wrapped:org.jbundle.util.osgi.wrapped.org.apache.http.client:4.1.2'
}
Add the above dependency in your build.gradle file.
This is happening because Android M does not supports the Apache HTTP API