Android Assert工具類

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/** Copyright (C) 2013 The Android Open Source Project** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**      http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package com.example.android.justforus;import android.content.ContentProvider;import android.content.ContentValues;import android.content.Context;import android.content.res.AssetFileDescriptor;import android.content.res.AssetManager;import android.database.Cursor;import android.database.MatrixCursor;import android.net.Uri;import android.provider.OpenableColumns;import android.util.Log;import java.io.FileNotFoundException;import java.io.IOException;import static java.net.URLConnection.guessContentTypeFromName;/** * Generic content provider, which makes any files available in this app‘s "assets" directory * available publicly. * * <p>To use, add the following to your AndroidManifest.xml: * * <code><pre> * <provider *   android:name=".AssetProvider" *   android:authorities="[YOUR CONTENT PROVIDER DOMAIN HERE]" *   android:grantUriPermissions="true" *   android:exported="true"/> * </pre></code> */public class AssetProvider extends ContentProvider {    /**     * Content provider authority that identifies data that is offered by this     * {@link AssetProvider}.     */    public static String CONTENT_URI = "com.example.android.justforus";    private static final String TAG = "AssetProvider";    AssetManager mAssets;    @Override    public boolean onCreate() {        Context ctx = getContext();        if (ctx == null) {            // Context not available. Give up.            return false;        }        mAssets = ctx.getAssets();        return true;    }    @Override    public String getType(Uri uri){        // Returns the MIME type for the selected URI, in conformance with the ContentProvider        // interface. Looks up the file indicated by /res/assets/{uri.path}, and returns the MIME        // type for that file as guessed by the URLConnection class.        // Setup        String path = uri.getLastPathSegment();        // Check if file exists        if (!fileExists(path)) {            return null;        }        // Determine MIME-type based on filename        return guessContentTypeFromName(uri.toString());    }    @Override    public AssetFileDescriptor openAssetFile (Uri uri, String mode)            throws FileNotFoundException, SecurityException {        // ContentProvider interface for opening a file descriptor by URI. This content provider        // maps all URIs to the contents of the APK‘s assets folder, so a file handle to        // /res/assets/{uri.path} will be returned.        // Security check. This content provider only supports read-only access. (Also, the contents        // of an APKs assets folder are immutable, so read-write access doesn‘t make sense here.)        if (!"r".equals(mode)) {            throw new SecurityException("Only read-only access is supported, mode must be [r]");        }        // Open asset from within APK and return file descriptor        String path = uri.getLastPathSegment();        try {            return mAssets.openFd(path);        } catch (IOException e) {            throw new FileNotFoundException();        }    }    /**     * Check if file exists inside APK assets.     *     * @param path Fully qualified path to file.     * @return true if exists, false otherwise.     */    private boolean fileExists(String path) {        try {            // Check to see if file can be opened. If so, file exists.            mAssets.openFd(path).close();            return true;        } catch (IOException e) {            // Unable to open file descriptor for specified path; file doesn‘t exist.            return false;        }    }    @Override    public Cursor query(Uri uri, String[] projection, String selection,                        String[] selectionArgs, String sortOrder) {        String path = uri.getLastPathSegment();        if (!fileExists(path)) {            Log.e(TAG, "Requested file doesn‘t exist at " + path);            return null;        }        // Create matrix cursor        if (projection == null) {            projection = new String[]{                    OpenableColumns.DISPLAY_NAME,                    OpenableColumns.SIZE,            };        }        MatrixCursor matrixCursor = new MatrixCursor(projection, 1);        Object[] row = new Object[projection.length];        for (int col = 0; col < projection.length; col++) {            if (OpenableColumns.DISPLAY_NAME.equals(projection[col])) {                row[col] = path;            } else if (OpenableColumns.SIZE.equals(projection[col])) {                try {                    AssetFileDescriptor afd = openAssetFile(uri, "r");                    if (afd != null) {                        row[col] = Long.valueOf(afd.getLength());                    }                    afd.close();                } catch (IOException e) {                    Log.e(TAG, e.toString());                }            }        }        matrixCursor.addRow(row);        return matrixCursor;    }    // Required/unused ContentProvider methods below.    @Override    public Uri insert(Uri uri, ContentValues contentValues) {        throw new RuntimeException("Operation not supported");    }    @Override    public int delete(Uri uri, String selection, String[] selectionArgs) {        throw new RuntimeException("Operation not supported");    }    @Override    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {        throw new RuntimeException("Operation not supported");    }}

　　

Android Assert工具類