The Android Widget Of Calculator

2016-07-04

在开始之前还是先了解下什么是widget吧？！其实对于Widget我们就可以简单明了地理解为一个快捷的小插件，我们经常看见的桌面天气、时钟、音乐这些就是啦。当我们需要添加widget时，只需要长按launcher界面的空白处选择WIDGETS即可看见APP的预置widget，然后选择一个自己想要的长按拖动到launcher即可。下面我就以计算器的widget为例，大概阐述下开发widget的流程。

http://10.120.10.101/source/xref/msm8939_r3_ap_2-1/packages/apps/Calculator/AndroidManifest.xml

<!-- Receiver for the widget -->
<receiverandroid:name=".widget.CalculatorWidget">
    <intent-filter>
        <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
    </intent-filter>
    <meta-data android:name="android.appwidget.provider"
        android:resource="@xml/calculator_widget_info" />
</receiver>

2. 添加MetaData对应的AppWidgetProviderInfo描述

http://10.120.10.101/source/xref/msm8939_r3_ap_2-1/packages/apps/Calculator/res/xml/calculator_widget_info.xml

<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialKeyguardLayout="@layout/widget"
    android:initialLayout="@layout/widget"
    android:minHeight="250dp"
    android:minWidth="250dp"
    android:previewImage="@drawable/widget_preview"
    android:resizeMode="vertical"
    android:updatePeriodMillis="0"
    android:widgetCategory="home_screen|keyguard" />

http://10.120.10.101/source/xref/msm8939_r3_ap_2-1/packages/apps/Calculator/res/layout/widget.xml

<?xmlversion="1.0"encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    <LinearLayout android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <LinearLayout android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@drawable/line"
            android:minHeight="60dp"
            android:orientation="horizontal">
         <LinearLayout android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="3">
                <TextView android:id="@+id/display"
                    style="@style/Theme.Calculator.Display.Widget"
                    android:layout_width="wrap_content"
                    android:layout_height="match_parent"
                    android:gravity="right|center_vertical"
                    android:longClickable="false"
                    android:visibility="gone" />
                    .
                    .
                    .
                <Button
                    android:id="@+id/plus"
                    style="@style/Theme.Calculator.ButtonStyle.Widget"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:layout_weight="1"
                    android:text="@string/op_add" />
           </LinearLayout>
       </LinearLayout>
    </LinearLayout>
</RelativeLayout>

注意，这里的APP Widget Layout都是基于RemoteViews的，并不是支持所有的layout和widget。
A RemoteViews object (and, consequently, an App Widget) can support the following layout classes:

FrameLayout LinearLayout RelativeLayout GridLayout

And the following widget classes:

AnalogClock Button Chronometer ImageButton

ImageView ProgressBar TextView ViewFlipper

ListView GridView StackView AdapterViewFlipper

Descendants of these classes are not supported.
RemoteViews also supports ViewStub, which is an invisible, zero-sized View you can use to lazily inflate layout resources at runtime.

4. 提供AppWidgetProvider实现

http://10.120.10.101/source/xref/msm8939_r3_ap_2-1/packages/apps/Calculator/src/com/android/calculator2/widget/CalculatorWidget.java

publicclassCalculatorWidgetextendsAppWidgetProvider {

    @Override
    public void onReceive(Contextcontext, Intentintent) {
        int appWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, 0);
        Stringvalue = getValue(context, appWidgetId);
        if(value.equals(context.getResources().getString(R.string.error_syntax))) value = "";
        mClearText = intent.getBooleanExtra(SHOW_CLEAR, false);
        final Context c = context;

        if(intent.getAction().equals(DIGIT_0)) {
            if(mClearText) {
                value = "";
                mClearText = false;
            }
            value += "0";
        }

        AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
        int[] appWidgetIds = appWidgetManager.getAppWidgetIds(newComponentName(context, CalculatorWidget.class));
        for(intappWidgetID : appWidgetIds) {
            updateAppWidget(context, appWidgetManager, appWidgetID);
        }
        super.onReceive(context, intent);
    }

    @Override
    public void onUpdate(Contextcontext, AppWidgetManagerappWidgetManager, int[] appWidgetIds) {
        for(int appWidgetID : appWidgetIds) {
            updateAppWidget(context, appWidgetManager, appWidgetID);
        }
    }

    private void updateAppWidget(Contextcontext, AppWidgetManagerappWidgetManager, intappWidgetId) {
        RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.widget);

        Stringvalue = getValue(context, appWidgetId);

        EquationFormatterformatter = new EquationFormatter();
        value = value.trim();
        value = formatter.addComas(newSolver(), value);

        int displayId = android.os.Build.VERSION.SDK_INT >
            android.os.Build.VERSION_CODES.JELLY_BEAN_MR1 ? R.id.display_long_clickable : R.id.display;

        remoteViews.setViewVisibility(displayId, View.VISIBLE);
        remoteViews.setTextViewText(displayId, value);
        remoteViews.setTextViewText(R.id.display, value);
        remoteViews.setViewVisibility(R.id.delete, mClearText ? View.GONE : View.VISIBLE);
        remoteViews.setViewVisibility(R.id.clear, mClearText ? View.VISIBLE : View.GONE);
        setOnClickListeners(context, appWidgetId, remoteViews);

        try {
            appWidgetManager.updateAppWidget(appWidgetId, remoteViews);
        } catch(Exception e) {
        }
    }
}