解决Android初学者创建时遇到Could not find any version that matches com.android.support:appcompat-v7:29.+. Versions that do not match: 26.0.0-alpha1 25.3.1 25.3.0 25.2.0 25.1.1 + 50 more

将app下build.gradle文件中
dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
 implementation 'com.android.support:appcompat-v7:29.+'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    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'
}修改为

dependencies {

    implementation fileTree(dir: 'libs', include: ['*.jar'])
 implementation 'com.android.support:appcompat-v7:+'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    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'
}

如果出现Dex file with version '38' cannot be used with min sdk level '29'.类似的错误
修改同文件下

android {
    compileSdkVersion 29
    defaultConfig {
        applicationId "com.example.z.test1"
   minSdkVersion 29
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
降低版本，我这边写为15

android {
    compileSdkVersion 29
    defaultConfig {
        applicationId "com.example.z.test1"
minSdkVersion 15
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }