安卓开发常用知识点& 安卓开发常见问题及解决方案
常用知识点===
一,Activity相关
- 1，判断activity是在前台运行，还是在后台运行
//当前activity是否在前台显示
private boolean isAPPforeground(final Context context) {
ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
List tasks = am.getRunningTasks(1);
if (!tasks.isEmpty()) {
ComponentName topActivity = tasks.get(0).topActivity;
if (topActivity.getClassName().equals(context.getClass().getName())) {
Log.i("qcl0403", "前台");
return true;
} else {
Log.i("qcl0403", "后台");
}
}
return false;
}
- 2，acitivity设置为singleTop或singleTask 模式时，相关文章跳本activity调整数据不改变问题
@Override
protected void onNewIntent(Intent intent) {
super.onNewIntent(intent);
setIntent(intent);
ARouter.getInstance().inject(this);
}
二，View相关
- 1 判断当前view是否在前台展示,我们这里以recyclerView为例
ViewTreeObserver treeObserver = recyclerView.getViewTreeObserver();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
treeObserver.addOnWindowFocusChangeListener(new ViewTreeObserver.OnWindowFocusChangeListener() {
@Override
public void onWindowFocusChanged(boolean hasFocus) {
/*
hasFocus是我们窗口状态改变时回传回来的值
true： 我们的view在前台展示
fasle: 熄屏，onpause，后台时展示
我们如果在每次熄屏到亮屏也算一次曝光的话，那这里为true的时候可以做统计
*/
}
});
}
- 2,RecyclerView滚动到指定位置，并置顶
LinearSmoothScroller smoothScroller = new LinearSmoothScroller
(ArticleDetailActivity.this) {
@Override
protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
//设置滑动1px所需时间
@Override
protected float calculateSpeedPerPixel
(DisplayMetrics displayMetrics) {
//缩短每px的滑动时间
float MILLISECONDS_PER_INCH = getResources().getDisplayMetrics()
.density * 0.03f;
return MILLISECONDS_PER_INCH / displayMetrics.density;
//返回滑动一个pixel需要多少毫秒
}
};
smoothScroller.setTargetPosition(position);
virtualLayoutManager.startSmoothScroll(smoothScroller);
三，适配相关
-1,判断手机是否有底部虚拟按键
/*
* 判断手机是否有底部虚拟按键
* */
public boolean checkDeviceHasNavigationBar(Context context) {
boolean hasNavigationBar = false;
Resources rs = context.getResources();
int id = rs.getIdentifier("config_showNavigationBar", "bool", "android");
if (id > 0) {
hasNavigationBar = rs.getBoolean(id);
}
try {
Class systemPropertiesClass = Class.forName("android.os.SystemProperties");
Method m = systemPropertiesClass.getMethod("get", String.class);
String navBarOverride = (String) m.invoke(systemPropertiesClass, "qemu.hw.mainkeys");
if ("1".equals(navBarOverride)) {
hasNavigationBar = false;
} else if ("0".equals(navBarOverride)) {
hasNavigationBar = true;
}
} catch (Exception e) {
}
return hasNavigationBar;
}
- 2，解决popupwindow在7.0以上机型设置居于view下方却盖在了view上面的问题
if (Build.VERSION.SDK_INT < 24) {
popupWindow.showAsDropDown(v);
} else {
int[] location = new int[2];
v.getLocationOnScreen(location);
int x = location[0];
int y = location[1];
popupWindow.showAtLocation(v, Gravity.NO_GRAVITY, 0, y + v.getHeight());
}
常见问题============
一，androidstudio编译相关
1， Error while Installing APK
解决方案：重新sync按钮编译下gradle就可以了
2，出现Execution failed for task类的错误
Error:Execution failed for task ‘:app:compileDebugJavaWithJavac’.
Compilation failed; see the compiler error output for details.
TaskExecutionException: Execution failed for task ‘:app:transformClassesWithAspectTransformForDebug’
解决方案：
首先找到Execution failed for task,然后取到后面的如上面红框里的信息
在命令行执行
./gradlew app:transformDexArchiveWithExternalLibsDexMergerForDebug --stacktrace --info
或者
./gradlew compileDebugJavaWithJavac --stackstrace
执行完成以后，搜索‘错误’就可以看到具体错误原因了
或者运行下面然后查看 Caused by的地方
./gradlew compileDebugSources --stacktrace -info
3 Could not find support-media-compat.aar
升级android studio到3.3版本，今天checkout到历史tag上运行android项目，死活报错
之前也有同事遇到过类似的问题： Could not find support-media-compat.aar
最后意外发现是google()仓库位置的问题
报错配置：
allprojects {
repositories {
flatDir {
dirs 'libs'
}
jcenter()
maven { url "https://jitpack.io" }
maven { url "https://dl.bintray.com/thelasterstar/maven/" }
maven {
url "http://maven.aliyun.com/nexus/content/repositories/releases"
}
mavenCentral()
google()
}
configurations.all {
resolutionStrategy {
force "com.android.support:appcompat-v7:$supportLibVersion"
}
}
}
把google()放到第一位即可
allprojects {
repositories {
google()
flatDir {
dirs 'libs'
}
jcenter()
maven { url "https://jitpack.io" }
maven { url "https://dl.bintray.com/thelasterstar/maven/" }
maven {
url "http://maven.aliyun.com/nexus/content/repositories/releases"
}
mavenCentral()
}
configurations.all {
resolutionStrategy {
force "com.android.support:appcompat-v7:$supportLibVersion"
}
}
}
4,could not find com.android.support:appconpat 如下图：
需要在project的build.gradle中allprojects 添加如下配置即可，添加下面代码到第一行。
maven { url “https://maven.google.com” }
5，报错：Annotation processors must be explicitly declared now.
在app的gradle文件中加入下面这句话：
android {
.....
defaultConfig {
......
//在下面添加这句话，然后重新编译，就OK了。
javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }
}