First prototype with prefix and suffix support.

Author: tobiasschuerg

.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild

.idea/codeStyles/Project.xml

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+package com.tobiasschuerg.prefixpostfix
+
+import android.os.Bundle
+import android.support.v7.app.AppCompatActivity
+import kotlinx.android.synthetic.main.activity_main.*
+
+class MainActivity : AppCompatActivity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_main)
+
+        edit_text_2.setPrefix("$")
+
+        edit_text_2.setText("$")
+
+        edit_text_2.setSuffix("$")
+    }
+}

app/src/main/java/com/tobiasschuerg/prefixpostfix/MainActivity.kt

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+package com.tobiasschuerg.prefixpostfix;
+
+import android.content.Context;
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.graphics.Rect;
+import android.graphics.Typeface;
+import android.support.v7.widget.AppCompatEditText;
+import android.text.TextPaint;
+import android.util.AttributeSet;
+
+/**
+ * Inspired by https://gist.github.com/morristech/5480419
+ */
+public class PrefixSuffixEditText extends AppCompatEditText {
+
+    private final Paint debugPaint;
+
+    // Stuff to do with our rendering
+    TextPaint mTextPaint = new TextPaint();
+    float       mFontHeight;
+    TagDrawable left;
+
+    // The actual suffix
+    String mSuffix = "";
+
+    // These are used to store details obtained from the EditText's rendering process
+    Rect line0bounds = new Rect();
+    int mLine0Baseline;
+
+    public PrefixSuffixEditText(Context context, AttributeSet attrs) {
+        super(context, attrs);
+
+        left = new TagDrawable(this);
+
+        mFontHeight = getTextSize();
+
+        mTextPaint.setColor(getCurrentHintTextColor());
+        mTextPaint.setTextSize(mFontHeight);
+        mTextPaint.setTextAlign(Paint.Align.LEFT);
+        mTextPaint.setAntiAlias(true);
+
+        debugPaint = new Paint();
+        debugPaint.setStyle(Paint.Style.STROKE);
+        debugPaint.setColor(Color.BLUE);
+
+
+        // Setup the left side
+        setCompoundDrawablesRelative(left, null, null, null);
+    }
+
+    @Override
+    public void setTypeface(Typeface typeface) {
+        super.setTypeface(typeface);
+        if (mTextPaint != null) {
+            // Sometimes TextView itself calls me when i'm naked
+            mTextPaint.setTypeface(typeface);
+        }
+
+        postInvalidate();
+    }
+
+    public void setPrefix(String s) {
+        left.setText(s);
+        setCompoundDrawablesRelative(left, null, null, null);
+    }
+
+    public void setSuffix(String s) {
+        mSuffix = s;
+        setCompoundDrawablesRelative(left, null, null, null);
+    }
+
+    @Override
+    public void onDraw(Canvas c) {
+        mLine0Baseline = getLineBounds(0, line0bounds);
+
+        super.onDraw(c);
+
+        // Now we can calculate what we need!
+        String text = getText().toString();
+        float textWidth = mTextPaint.measureText(left.text + text) + getPaddingLeft();
+
+
+        c.drawRect(line0bounds, debugPaint);
+
+        // We need to draw this like this because
+        // setting a right drawable doesn't work properly and we want this
+        // just after the text we are editing (but untouchable)
+        float y2 = line0bounds.bottom - mTextPaint.descent();
+        c.drawText(mSuffix, textWidth, y2, mTextPaint);
+    }
+
+}

app/src/main/java/com/tobiasschuerg/prefixpostfix/PrefixSuffixEditText.java

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+package com.tobiasschuerg.prefixpostfix;
+
+import android.graphics.Canvas;
+import android.graphics.ColorFilter;
+import android.graphics.PixelFormat;
+import android.graphics.drawable.Drawable;
+import android.support.annotation.NonNull;
+
+// This is for the prefix.
+// It is a drawable for rendering text
+public class TagDrawable extends Drawable {
+
+    private PrefixSuffixEditText extendedEditText;
+    public String text = "";
+
+    public TagDrawable(PrefixSuffixEditText extendedEditText) {
+        this.extendedEditText = extendedEditText;
+    }
+
+    public void setText(String s) {
+        text = s;
+
+        // Tell it we need to be as big as we want to be!
+        setBounds(0, 0, getIntrinsicWidth(), getIntrinsicHeight());
+
+        invalidateSelf();
+    }
+
+    @Override
+    public void draw(@NonNull Canvas canvas) {
+        // I don't know why this y works here, but it does :)
+        // (aka if you are from Google/are Jake Wharton and I have done it wrong, please tell me!)
+        canvas.drawText(text, 0, extendedEditText.mLine0Baseline + canvas.getClipBounds().top, extendedEditText.mTextPaint);
+    }
+
+    @Override
+    public void setAlpha(int i) {
+    }
+
+    @Override
+    public void setColorFilter(ColorFilter colorFilter) {
+    }
+
+    @Override
+    public int getOpacity() {
+        return PixelFormat.OPAQUE;
+    }
+
+    @Override
+    public int getIntrinsicHeight() {
+        return (int) extendedEditText.mFontHeight;
+    }
+
+    @Override
+    public int getIntrinsicWidth() {
+        return (int) extendedEditText.mTextPaint.measureText(text);
+    }
+}

app/src/main/java/com/tobiasschuerg/prefixpostfix/TagDrawable.java

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+// Top-level build file where you can add configuration options common to all sub-projects/modules.
+
+buildscript {
+    ext.kotlin_version = '1.2.61'
+    repositories {
+        google()
+        jcenter()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:3.1.4'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+
+        // NOTE: Do not place your application dependencies here; they belong
+        // in the individual module build.gradle files
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        jcenter()
+    }
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}

build.gradle

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+# Project-wide Gradle settings.
+# IDE (e.g. Android Studio) users:
+# Gradle settings configured through the IDE *will override*
+# any settings specified in this file.
+# For more details on how to configure your build environment visit
+# http://www.gradle.org/docs/current/userguide/build_environment.html
+# Specifies the JVM arguments used for the daemon process.
+# The setting is particularly useful for tweaking memory settings.
+org.gradle.jvmargs=-Xmx1536m
+# When configured, Gradle will run in incubating parallel mode.
+# This option should only be used with decoupled projects. More details, visit
+# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
+# org.gradle.parallel=true

gradle.properties

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+#Mon Sep 10 15:22:37 CEST 2018
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip