适配完结篇一 - 超快速的Android屏幕适配方式

private void getDisplayInfo(){
    Resources resources=getResources();
    DisplayMetrics displayMetrics = resources.getDisplayMetrics();
    float density = displayMetrics.density;
    int densityDpi = displayMetrics.densityDpi;
    Log.i(TAG, "density = " + density);
    Log.i(TAG, "densityDpi = " + densityDpi);
}

density = 3.0 
densityDpi = 480

The screen density expressed as dots-per-inch. 
May be either DENSITY_LOW，DENSITY_MEDIUM or DENSITY_HIGH

public static float applyDimension(int unit, float value,
                                       DisplayMetrics metrics)
    {
        switch (unit) {
        case COMPLEX_UNIT_PX:
            return value;
        case COMPLEX_UNIT_DIP:
            return value * metrics.density;
        case COMPLEX_UNIT_SP:
            return value * metrics.scaledDensity;
        case COMPLEX_UNIT_PT:
            return value * metrics.xdpi * (1.0f/72);
        case COMPLEX_UNIT_IN:
            return value * metrics.xdpi;
        case COMPLEX_UNIT_MM:
            return value * metrics.xdpi * (1.0f/25.4f);
        }
        return 0;
    }

要求得的1pt实际对应的px / 屏幕宽度px = 1px / 设计图宽度px
要求得的1pt实际对应的px = 屏幕宽度px / 设计图宽度px

然后
metrics.xdpi * (1.0f/72) = 对于1pt表示的像素
metrics.xdpi = 1*72=72

        final Point size = new Point();
        ((WindowManager) context.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getSize(size);
        final Resources resources = context.getResources();
        resources.getDisplayMetrics().xdpi = size.x / designWidth * 72f;

package xxx.yyy.zzz;

import java.lang.reflect.Field;

import android.app.Activity;
import android.app.Application;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Point;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.TypedValue;
import android.view.WindowManager;

/**
 * Created by Caodongyao 
 * 转载请联系作者并注明出处 http://www.jianshu.com/p/b6b9bd1fba4d
 * 使用方法: Application#onCreate中调用一次即可
 */
public class ScreenHelper {
    /**
     * 重新计算displayMetrics.xhdpi, 使单位pt重定义为设计稿的相对长度
     * 
     * @see #activate()
     *
     * @param context
     * @param designWidth
     *            设计稿的宽度
     */
    public static void resetDensity(Context context, float designWidth) {
        if (context == null) return;
        final Point size = new Point();
        ((WindowManager) context.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getSize(size);
        final Resources resources = context.getResources();
        resources.getDisplayMetrics().xdpi = size.x / designWidth * 72f;

        DisplayMetrics metrics = getMetricsOnMiui(resources);
        if (metrics != null) {
            metrics.xdpi = size.x / designWidth * 72f;
        }
    }

    /**
     * 恢复displayMetrics为系统原生状态，单位pt恢复为长度单位磅
     * 
     * @see #inactivate()
     *
     * @param context
     */
    public static void restoreDensity(Context context) {
        context.getResources().getDisplayMetrics().setToDefaults();

        DisplayMetrics metrics = getMetricsOnMiui(context.getResources());
        if (metrics != null)
            metrics.setToDefaults();
    }

    // 解决MIUI更改框架导致的MIUI7+Android5.1.1上出现的失效问题(以及极少数基于这部分miui去掉art然后置入xposed的手机)
    private static DisplayMetrics getMetricsOnMiui(Resources resources) {
        if ("MiuiResources".equals(resources.getClass().getSimpleName())
                || "XResources".equals(resources.getClass().getSimpleName())) {
            try {
                Field field = Resources.class.getDeclaredField("mTmpMetrics");
                field.setAccessible(true);
                return (DisplayMetrics) field.get(resources);
            } catch (Exception e) {
                return null;
            }
        }
        return null;
    }

    private Application.ActivityLifecycleCallbacks mActivityLifecycleCallbacks;
    private Application mApplication;
    private float mDesignWidth;
    
    /**
     *
     * @param application
     *            application
     * @param width
     *            设计稿宽度
     */
    public ScreenHelper(Application application, float width) {
        mApplication = application;
        mDesignWidth = width;

        mActivityLifecycleCallbacks = new Application.ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                // 通常情况下application与activity得到的resource虽然不是一个实例，但是displayMetrics是同一个实例，只需调用一次即可
                // 为了面对一些不可预计的情况以及向上兼容，分别调用一次较为保险
                resetDensity(mApplication, mDesignWidth);
                resetDensity(activity, mDesignWidth);
            }

            @Override
            public void onActivityStarted(Activity activity) {
                resetDensity(mApplication, mDesignWidth);
                resetDensity(activity, mDesignWidth);
            }

            @Override
            public void onActivityResumed(Activity activity) {
                resetDensity(mApplication, mDesignWidth);
                resetDensity(activity, mDesignWidth);
            }

            @Override
            public void onActivityPaused(Activity activity) {

            }

            @Override
            public void onActivityStopped(Activity activity) {

            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

            }

            @Override
            public void onActivityDestroyed(Activity activity) {

            }
        };
    }

    /**
     * 激活本方案
     */
    public void activate() {
        resetDensity(mApplication, mDesignWidth);
        mApplication.registerActivityLifecycleCallbacks(mActivityLifecycleCallbacks);
    }

    /**
     * 恢复系统原生方案
     */
    public void inactivate() {
        restoreDensity(mApplication);
        mApplication.unregisterActivityLifecycleCallbacks(mActivityLifecycleCallbacks);
    }
    
    /**
     * 转换pt为px
     * @param context context
     * @param value 需要转换的pt值，若context.resources.displayMetrics经过resetDensity()的修改则得到修正的相对长度，否则得到原生的磅
     * @return px值
     */
    public static float pt2px(Context context, float value){
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_PT, value, context.getResources().getDisplayMetrics());
    }
}