Android 常用小知识

• TextView 添加下划线

        TextView textView = findViewById(R.id.textView);
        String text = "这是一段测试文字";
        //方法一
        textView.setText(Html.fromHtml(String.format("<u>%s</u>", text)));
        //方法二
        //<string name="example"><u>这是一段测试文字</u></string>}
        textView.setText(R.string.example);
        //方法三
        textView.getPaint().setFlags(textView.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);
        //方法四
        SpannableString ss = new SpannableString(text);
        ss.setSpan(new UnderlineSpan(), 0, text.length(), Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
        textView.setText(ss);

• Webview 加载html

        //加载url
        webView.loadUrl("http://www.baidu.com");
        //加载asset目录下html文件
        webView.loadUrl("file:///android_asset/index.html");
        //加载 手机内部存储或sd卡 内的html文件
        webView.loadUrl("file:///storage/emulated/0/index.html");

• ListView，RecyclerView等设置具有padding的分割线
  设置分割线，我们只需要提供DividerDrawable即可，示例代码如下

        //ListView设置分割线
        mListView.setDivider(drawable);
        //RecyclerView设置分割线
        DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
        dividerItemDecoration.setDrawable(drawable);
        mRecyclerView.addItemDecoration(dividerItemDecoration);

方式一：使用xml，drawable/divider.xml

<inset xmlns:android="http://schemas.android.com/apk/res/android"
       android:insetLeft="15dp"
       android:insetRight="15dp" >
    <shape>
        <size android:height="1dp"/>
        <solid android:color="@color/color_divider" />
    </shape>
</inset>

方式二：使用代码：

        ShapeDrawable shapeDrawable = new ShapeDrawable();
        shapeDrawable.setColorFilter(color, mode);
        shapeDrawable.setIntrinsicHeight(height);
        InsetDrawable drawable = new InsetDrawable(shapeDrawable, insetLeft, insetTop, insetRight, insetBottom);

• TabLayout常见用法

1. 设置字体大小
   定义style，如下：

<style name="TabLayoutStyle" parent="Base.Widget.Design.TabLayout">
    <item name="android:textSize">12sp</item>
    <item name="android:textAllCaps">true</item>
</style>

然后在xml中使用，如下：

<android.support.design.widget.TabLayout
                android:id="@+id/tabLayout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:tabGravity="fill"
                app:tabIndicatorColor="@color/colorPrimaryDark"
                app:tabIndicatorHeight="2dp"
                app:tabMode="fixed"
                app:tabSelectedTextColor="@color/colorPrimaryDark"
                app:tabTextAppearance="@style/TabLayoutStyle"
                app:tabTextColor="@color/colorGrey" />

2.设置Tab间分割线，方法如下

View root = tabLayout.getChildAt(0);
if (root instanceof LinearLayout) {
      ((LinearLayout) root).setShowDividers(LinearLayout.SHOW_DIVIDER_MIDDLE);
      GradientDrawable drawable = new GradientDrawable();
      drawable.setColor(Color.BLACK);
      drawable.setSize(2, 1);
      ((LinearLayout) root).setDividerDrawable(drawable);
}

• 设置AppCompatRatingBar仅仅显示，不可交互

android:isIndicator="true"

• CardView设置透明背景的问题
  方法一：XML设置cardBackgroundColor属性为TRANSPARENT
  方法二：代码设置setCardBackgroundColor(Color.TRANSPARENT)
  方法三：代码设置setBackgroundColor(Color.TRANSPARENT)
  注意：CardView在XML设置background是无效的，原因很简单，看源代码即可：

//CardView的构造函数中会调用以下代码
TypedArray a = context.obtainStyledAttributes(attrs, styleable.CardView, defStyleAttr, style.CardView);
ColorStateList backgroundColor;
if (a.hasValue(styleable.CardView_cardBackgroundColor)) {
    backgroundColor = a.getColorStateList(styleable.CardView_cardBackgroundColor);
} else {
    TypedArray aa = this.getContext().obtainStyledAttributes(COLOR_BACKGROUND_ATTR);
    int themeColorBackground = aa.getColor(0, 0);
    aa.recycle();
    float[] hsv = new float[3];
    Color.colorToHSV(themeColorBackground, hsv);
    backgroundColor = ColorStateList.valueOf(hsv[2] > 0.5F ? this.getResources().getColor(color.cardview_light_background) : this.getResources().getColor(color.cardview_dark_background));
}
///省略...
IMPL.initialize(this.mCardViewDelegate, context, backgroundColor, radius, elevation, maxElevation);
//IMPL.initialize会调用mCardViewDelegate.setCardBackground方法
//而mCardViewDelegate.setCardBackground最终会调用CardView.this.setBackgroundDrawable(drawable)方法

由以上分析可知，在XML通过background属性设置的背景色最终会被冲掉，所以CardView在XML里设置background是无效的

• 解决发送邮件时换行符\n不生效的问题

//解决办法：设置Type为text/html，换行符使用</br>
try {
    Intent intent = new Intent(Intent.ACTION_SENDTO);
    intent.setType("text/html")
                    .setData(Uri.parse("mailto:"))// only email apps should handle this
                    .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
                    .addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP)
                    .putExtra(Intent.EXTRA_EMAIL, addresses)
                    .putExtra(Intent.EXTRA_SUBJECT, "SUBJECT")
                    .putExtra(Intent.EXTRA_TEXT, "<\\br><\\br>text<\\br>");
    if (intent.resolveActivity(context.getPackageManager()) != null) {
        context.startActivity(intent);
    }
} catch (Exception e) {
}