Android开发问题汇总(三)

android, archives

1. How to define custom attributes?

A:Currently the best documentation is the source. You can take a look at it here(arrts.xml).

You can define attributes in the top <resources> element or inside of a <declare-styleable> element. If I’m going to use an attr in more than on place I put it in the root element. Note , all attributes share the same global namespace. That means that even if you create a new attribute inside of a <declare-styleable> element it can be used outside of it and you cannot create another attribute with the same name of a different type.

An <attr> element has two xml attributes name and format. name lets you call it something and this how you end up refering to it in code, e.g., R.attr.my_attribute. The format attribute can have different values depending on the type of attribute you want.

  • reference - if it references another resource id(e.g, “@color/my_color”, “@layout/my_layout”)
  • color
  • boolean
  • dimension
  • float
  • integer
  • string
  • fraction
  • enum - normally implicitly defined
  • flag - normally implicitly defined

You can set the format to multiple types by using |, e.g., format="reference|color".

enum attributes can be defined as follows:

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<attr name="my_enum_attr"> 
    <enmu name="value1" value="1" />
    <enmu name="value2" value="2" />
</attr>

flag attributes are similar except the values need to defined so they can be bit ored together:

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<attr name="my_flag_attr">
    <flag name="fuzzy" value="0x01" />
    <flag name="cold" value="0x02" />
</attr>

In addition to attributes there is the <declare-styleable> element. This allows you to define attributes a custom view can use. You do this by specifying an <attr> element, if it was previously defined you do not specify the format. If you wish to reuse an android attr, for example android:gravity, then you can do that in the name, as follows.

An example of a custom view <declare-styleable>:

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<declare-styleable name="MyCustomView"> 
    <attr name="my_custom_attribute" />
    <attr name="android:gravity" />
</declare-styleable>

When defining you custom attributes in XML on you need to do a few things.

First you must declare a namespace to find your attributes. You do this on the root layout element. Normal there is only xmlns:android="http//schemas.android.com/apk/res/android". You must now also add xmlns:app="http://schemas.android.com/apk/res-auto".

Example:

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:whatever="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">

<org.example.mypackage.MyCustomView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
whatever:my_custom_attribute="Hello, world!" />
</LinearLayout>

Finally, to access that custom attribute you normally do so in the constructor of you custom view as follows:

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public MyCustomView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyCustomView, defStyle, 0);

    String str = a.getString(R.styleable.MyCustomView_my_custom_attribute);

    //do something with str

    a.recycle();
}

Reference:Defining custom attrs

2. How to get Uri from raw file?

A: Uri url = Uri.parse("android.resource://" + getPackageName() + "/" + R.raw.usa_for_africa_we_are_the_world);

Reference:Android - How to get Uri from raw file?

3. How to display all music on SD card?

A: We can use loader perform this work,

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public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    return new CursorLoader(getActivity(), MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, new String[] { MediaStore.Audio.Media.DISPLAY_NAME }, null, null,
      "LOWER(" + MediaStore.Audio.Media.TITLE + ") ASC");    
}

Reference:Display all music on SD card

4. Call require API level 21(current min is 10):android.content.Context#getDrawable.

A:ContextCompat.getDrawable(getActivity(), R.drawable.name);

Reference:Android getResources().getDrawable() deprecated API 22

5. Android Studio 工程卡在 Refreshing ‘Project Name’ Gradle project 或 gradle building project。

A: Android Studio 更新到 2.3 后，打开之前的项目卡在 Refreshing ‘Project Name’ Gradle project, 问题的原因是新版本的 Android Studio 使用的也是新版本的 Gradle,由于网络原因导致更新 Gradle 很慢，我们可以手动下载 Gradle 来解决这个问题。

  1. 根据项目中 gradle-wrapper.properties 文件的配置，手动下载合适版本的 gradle;
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distributionUrl=https\://services.gradle.org/distributions/gradle-3.3-all.zip
  1. 将下载好的 gradle 移动到合适的位置;
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// Windows
C:\Users\用户名.gradle\wrapper\dists\gradle-x.xx-all\xxxxxxxxxxxx
// MacOS
$HOME/.gradle/wrapper/dists/gradle-3.3-all/55gk2rcmfc6p2dg9u9ohc3hw9/
  1. 重启 Android Studio。

Reference: Android Studio解决refreshing gradle project
Androidstudio配置本地Gradle

6. 怎么改变 EditText 输入框底部线条的颜色？

A: 在 style.xml 中覆盖 colorControlActivated, ColorControlHighlight 和 colorControlNormal

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<style name="Theme.App.Base" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorControlNormal">#c5c5c5</item>
    <item name="colorControlActivated">@color/accent</item>
    <item name="colorControlHighlight">@color/accent</item>
</style>

Reference:Changing EditText bottom line color with appcompat v7

7.如何隐藏软键盘？

A:

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// Check if no view has focus:
View view = this.getCurrentFocus();
if (view != null) {  
    InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
    imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
}

Reference:Close/hide the Android Soft Keyboard

8.ListView 中的 EditText 捕获焦点异常。

A:在 manifest 中配置下 Activity :

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<activity android:name= ".yourActivity" android:windowSoftInputMode="adjustPan"/>

Reference:Focusable EditText inside ListView

9.Android Studio 如何设置使用本地 gradle?

A:

  1. 下载 gradle;
  2. 解压 gradle 到合适的目录，例如 /Users/meiliang/.gradle/local_gradle_distribution/;
  3. 在 Android Studio 中设置 gradle home:
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 Android Studio > Preference... > Build,Excution,Deployment > Gradle > User local gradle distribution > Gradle home

 Gradle home :/Users/meiliang/.gradle/local_gradle_distribution/gradle-3.3

10.Could not find method leftShift() for arguments on task of type org.gradle.api.DefaultTask

A:<< was deprecated in 4.x and removed in 5.0.

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task createDB<<{
    description= "Creates the Database. Needs database name to be passed (like: -PdbName=someDBname)"
    sql = Sql.newInstance( 'jdbc:mysql:thin://localhost:3306/', mysqlUser, mysqlPassword, 'org.drizzle.jdbc.DrizzleDriver' )
    sql.execute( 'create database '+"`$dbName`" )
}

// Change to 
task createDB {
   description= "Creates the Database. Needs database name to be passed (like: -PdbName=someDBname)"
   doLast {    
    sql = Sql.newInstance( 'jdbc:mysql:thin://localhost:3306/', mysqlUser, mysqlPassword, 'org.drizzle.jdbc.DrizzleDriver' )
    sql.execute( 'create database '+"`$dbName`" )
   } 
}

Reference:[Could not find method leftShift() for arguments on task of type org.gradle.api.DefaultTask)[https://discuss.gradle.org/t/could-not-find-method-leftshift-for-arguments-on-task-of-type-org-gradle-api-defaulttask/30614)

11.How to unzip and view content of aar?

A:

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$jar -xvf app-debug.aar

12.How to update local aar module?

A:

  1. Update yourLib.aar file in module, eg. copy new version aar to module dir
  2. Sync Project with Gradle Files

13.Where is the merged AndroidManifest.xml?

A:

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/project/module/build/intermediates/manifests/full/debug/AndroidManifest.xml

Reference:MANIFEST MERGER: It is possible to see the resulting mixed Manifest?