Android studio
情况一：
描述：写Android app时，出现activity对应的layout预览图所显示的activity是有标题栏的，但是运行该app，无论是模拟器还是真机，却出现没有了标题栏的情况，而自己没有特地隐藏标题栏。
解决：此时出现标题栏消失可能是因为activity继承是Activity而不是AppCompatActivity，而我们在创建app之初，AS默认是继承AppCompatActivity，AndroidManifest.xml文件里对应的theme则是
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
情况二：
描述：多个Fargment使用同一layout ID，在进行来回切换操作时出现“Java.lang.IllegalStateException: commit already called”的错误。
解决：由于本人将FragmentTransaction变量定义为全局变量，导致只能commit一次，所以只要将FragmentTransaction变量定义为局部变量即可。
情况三：
描述：使用FragmentTransaction的replace方法时出现错误：
'replace(int, android.app.Fragment, java.lang.String)' in 'android.app.FragmentTransaction' cannot be applied to '(int, com.jarwell.learnactionbar.ContentFragment, java.lang.String)'
解决：此种情况发生在ContentFragment所继承的Fragment是android.support.v4.app.Fragment，而FragmentTransaction对象所导入的包是android.app.FragmentTransaction，由此出现不兼容的情况。据此只要统一导入包的类型即可，譬如可以分别：import android.app.Fragment和import android.app.FragmentTransaction
情况四：
描述：如何添加assets文件夹？
解决：
首先，在“工程名.iml”文件里的configuration标签下添加以下代码：
<option name="ASSETS_FOLDER_RELATIVE_PATH" value="/src/main/assets"/>
然后，在main文件夹里新建一个子文件夹并命名为assets，到此完成，之后就可以往里面添加文件了。
情况五：
描述：在JSON解析时出现了以下错误日志：
08-31 15:36:59.369 13195-13195/? E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.monkeyPatchExistingResources
08-31 15:36:59.370 13195-13195/? E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.pruneResourceCache
08-31 15:36:59.381 13195-13195/? E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.382 13195-13195/? E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.382 13195-13195/? E/dalvikvm: Could not find class 'android.media.session.MediaController', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.383 13195-13195/? E/dalvikvm: Could not find class 'android.widget.Toolbar', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.386 13195-13195/? E/dalvikvm: Could not find class 'android.app.ActivityManager$TaskDescription', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.391 13195-13195/? E/dalvikvm: Could not find class 'android.app.SharedElementCallback', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.393 13195-13195/? E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.395 13195-13195/? E/dalvikvm: Could not find class 'android.transition.TransitionManager', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.402 13195-13195/? E/dalvikvm: Could not find class 'android.app.SharedElementCallback', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.410 13195-13195/? E/dalvikvm: Could not find class 'android.app.assist.AssistContent', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.412 13195-13195/? E/dalvikvm: Could not find class 'android.view.SearchEvent', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.416 13195-13195/? E/dalvikvm: Could not find class 'android.os.PersistableBundle', referenced from method com.jarwell.learnjson.MainActivity.access$super
08-31 15:36:59.477 13195-13195/? E/dalvikvm: Could not find class 'android.graphics.drawable.RippleDrawable', referenced from method android.support.v7.widget.AppCompatImageHelper.hasOverlappingRendering
08-31 15:37:32.664 518-795/? E/FWKEXT: Enter GetCurrentOP
解决：出现以上情况，是因为代码所调用的一些方法只能在较高的API level（高于minSdkVersion）上使用，而调试用的机子或模拟器所用的SDK Version小于该API level。如日志第一行提示中的ArrayMap，通过查看Android官方API可得到如下信息：
Added in API level 19
而本人的project的build.gradle如下：
apply plugin: 'com.android.application'
android {
compileSdkVersion 24
buildToolsVersion "24.0.0"
defaultConfig {
applicationId "com.jarwell.learnjson"
minSdkVersion 17
targetSdkVersion 24
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-v7:24.2.0'
}
其中所使用的minSdkVersion为17，targetSdkVersion 为24，而run app的机子对应的API level恰好是17(17<19<24)，因此出现了以上的错误日志信息，尝试用level为19以上的机子或模拟器则运行正常。
