android系统中如何判断一个文件是否存在？

sd卡目录请不要直接使用/storage/sdcard0/，你这样试试\x0d\x0aString SDPATH = Environment.getExternalStorageDirectory().getPath() + "//" \x0d\x0aFile f = new File(SDPATH +"/Manual/test.pdf")\x0d\x0a另外你是不是忘记加权限了

sd卡目录请不要直接使用/storage/sdcard0/，你这样试试

String SDPATH = Environment.getExternalStorageDirectory().getPath() + "//"

File f = new File(SDPATH +"/Manual/test.pdf")

另外你是不是忘记加权限了<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Android系统中，判断应用有无安装有两种方式：

1.根据包名判断,以下为判断代码：

public boolean checkApkExist(Context context, String packageName) {

if (packageName == null || “”.equals(packageName))

return false

try {

ApplicationInfo info = context.getPackageManager()

.getApplicationInfo(packageName,

PackageManager.GET_UNINSTALLED_PACKAGES)

return true

} catch (NameNotFoundException e) {

return false

}

}

2. 根据Intent判断，以下为判断代码：

public boolean checkApkExist(Context context, Intent intent) {

List<ResolveInfo>list = context.getPackageManager().queryIntentActivities(intent, 0)

if(list.size() >0){

return true

}

return false

}

public boolean checkApkExist(Context context, String packageName) {

if (packageName == null || “”.equals(packageName)) return false

try {

ApplicationInfo info = context.getPackageManager() .getApplicationInfo(packageName, PackageManager.GET_UNINSTALLED_PACKAGES)return true

} catch (NameNotFoundException e) { return false}

}

public boolean checkApkExist(Context context, Intent intent) {

List<ResolveInfo>list = context.getPackageManager()

.queryIntentActivities(intent, 0)

if (list.size() >0) {

return true

}

return false

}

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