TextView加载大文本发生卡顿

Posted 2021-07-10 lauryn_yin

大概100多kb的文本内容的时候，会发生这个问题，采用的就是原生的TextView，原因的话网上讲得也比较详细，有的甚至连加载流程也都讲出来了，总的来说就是描画文本的作业是在UI线程里进行的

解决方案的话，网上提了大概四个吧。

方法一，把TextView的宽度设定为一个数字或者match_parent。NG，至少对我来说不起任何作用

方法二，使用androidx.appcompat.widget.AppCompatTextView。同上

方法三，在方法二的基础上，采用下述方法，加载速度肉眼可见的有提升，关键是改动量比较小

import androidx.appcompat.widget.AppCompatTextView;	
import androidx.core.text.PrecomputedTextCompat;	
import java.util.concurrent.Future;
。。。。
//关键代码
Future<PrecomputedTextCompat> future = PrecomputedTextCompat.getTextFuture(contentDelayed, txtViewContent.getTextMetricsParamsCompat(), null);
txtViewContent.setTextFuture(future);

方法四，相对方法三来说，改动量有点大:使用StaticLayout，具体原因以及理由网上有，可以自行百度。其实这个方法相当于是一个自定义view了。

参考：https://www.jianshu.com/p/a9d6fbf20642

import android.content.Context;
import android.graphics.Canvas;
import android.text.Layout;
import android.util.AttributeSet;
import android.view.View;

public class StaticLayoutView extends View {

	private Layout mLayout = null;

	private int mWidth;
	private int mHeight;

	public StaticLayoutView(Context context) {
		super(context);
	}

	public StaticLayoutView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}

	public StaticLayoutView(Context context, AttributeSet attrs,int defStyleAttr) {
		super(context, attrs, defStyleAttr);
	}

	public void setLayout(Layout layout) {
		if (layout == null) {
			return;
		}
		
		mLayout = layout;
		if (mLayout.getWidth() != mWidth || mLayout.getHeight() != mHeight) {
			mWidth = mLayout.getWidth();
			mHeight = mLayout.getHeight();
			requestLayout();
		}
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.save();
		if (mLayout != null) {
			mLayout.draw(canvas, null, null, 0);
		}
		canvas.restore();
	}

	@Override
	protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
		super.onLayout(changed, left, top, right, bottom);
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		if (mLayout != null) {
			setMeasuredDimension(mLayout.getWidth(), mLayout.getHeight());
		} else {
			super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		}
	}

}

public class StaticLayoutManager {

    public StaticLayout longStringLayout;

    private TextPaint textPaint;
    private Layout.Alignment alignment;


    private int hardCodeWidth;

    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
    public void initLayout(Context context, CharSequence longString) {

        textPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
        textPaint.density = context.getResources().getDisplayMetrics().density;
        textPaint.setTextSize(DisplayUtils.fromDPtoPix(context, DisplayUtils.TEXT_SIZE_DP));
        
        alignment = Layout.Alignment.ALIGN_NORMAL;

        hardCodeWidth = DisplayUtils.getScreenWidth(context);

        longStringLayout = new StaticLayout(longString, textPaint, hardCodeWidth, alignment, 1.0f, 0f, true);
    }


    public StaticLayout getLongStringLayout() {
        return longStringLayout;
    }

    private static StaticLayoutManager INSTANCE = null;

    public static StaticLayoutManager getInstance() {
        if (INSTANCE == null) {
            INSTANCE = new StaticLayoutManager();
        }
        return INSTANCE;
    }
}

使用方法

public class StaticLayoutAty extends AppCompatActivity {

    private String readFile() {
        try {
            InputStream is = getAssets().open("0.txt");
            int size = is.available();
            byte[] buffer = new byte[size];
            is.read(buffer);
            is.close();
            return new String(buffer);
        } catch (IOException e) {
            return "读取错误...";
        }
    }

    StaticLayoutView staticLayoutView;
    ProgressDialog pd;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_static_layout_aty);
        staticLayoutView = findViewById(R.id.static_content);
        pd = new ProgressDialog(this);
        pd.show();
        new Thread(new Runnable() {
            @Override
            public void run() {
                StaticLayoutManager.getInstance().initLayout(StaticLayoutAty.this,  readFile());

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        staticLayoutView.setLayout(StaticLayoutManager.getInstance().getLongStringLayout());
                        Toast.makeText(StaticLayoutAty.this, "init span finish", Toast.LENGTH_LONG).show();
                        pd.dismiss();
                    }
                });
            }
        }).start();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorAccent"
    tools:context=".activity.StaticLayoutAty">

    <com.xx.StaticLayoutView
        android:id="@+id/static_content"
        android:layout_width="fill_parent"
        android:layout_height="match_parent"/>

</ScrollView>

PS:方法四在试验的时候还是有问题，progressDialog消失了10多秒之后，文本才加载出来，而且还会ANR，可能是用的不对？